Disassembly: Radiator Fan Control

[Greg E]

This was a puzzle piece that was extremely difficult to figure out. The format for this table in the code is different than most others as it's axis is static and it has no look up sub call.... Then it's reference is in a completely random area in the code with no direct references to coolant temp. Then, when I did finally figure all this out, the values in the table all seemed really high.

So a few days after testing, I've finally verified I found the table that controls when the radiator fans kick on. This would also explain some of the overheating issues most people experience with any FMIC and the stock fans. IMHO The issue isn't so much their airflow as it is just the fact the fans don't kick on till such a high temp!

Never fails, there's always one car in a 3/S cruise with a FMIC and stock fans that ends up overheating.... I've always fixed it by either hotwiring the fans to stay on all the time, or pulling the AC clutch fuse and having them drive around with the AC switched on. Solves the overheating issue.

Opened up the EVO disassembly and went hunting for the same table. The logic was completely different but when I did finally find it, the values populated inside seemed more what I was expecting. Since the EVO came with a FMIC stock and you never hear of overheating issues, these values may help a LOT for you guys with a FMIC.

http://i.imgur.com/yw7Op.jpg

The numbers you see in these tables are the temperature (degF) that trigger when each fan or fan state engages. The stock 99 VR4 table is up top and the EVO8 table is on the bottom. As you can see, the EVO table is MUCH MUCH more conservative. In fact, I'm running it in my 98 right now!

Sorry 1G guys... Unless you wire in the fan controller setup from a 2G VR4, this isn't going to be very useful to you.

[jba3]

Perfect timing. I've got my car apart for a bunch of things, including an FMIC install. I've got the flashable ECU ready to go, so I'll gladly test this out on my 95. Great job!

[TurboSinceBirth]

Wow, that's very interesting. Do you have any idea if this would be affected if you had two driver's side fans installed? I still have both stock fans but bought another A/C fan to replace the passenger one plus it would free up more room too. I'm assuming that if it was wired up correctly it would make no difference. I will have to check into it though.

[Greg E]

Wow, that's very interesting. Do you have any idea if this would be affected if you had two driver's side fans installed? I still have both stock fans but bought another A/C fan to replace the passenger one plus it would free up more room too. I'm assuming that if it was wired up correctly it would make no difference. I will have to check into it though.

I would assume the same thing too. That would have to be a trial and error thing. Unfortunately, I ditched my spare fans a few months ago. :(

[TurboSinceBirth]

I should have the flashed ECU installed here before too long and I have probably 4 or 5 A/C fans here so I'm sure I can figure it out.

[Alex3000gt]

On a 1st gen you can simply swap the temperature sensor connectors at the bottom of the radiator.

This makes it so that both fans come on whenever the coolant reaches the temperature threshold, as opposed to one coming on initially then both turning on later.

I'd have to look in the shop manual for the actual numbers, but I think the first threshold was 190F and the other was 210F?

[Greg E]

I made a mistake. I wrote 75mph and its supposed to be 75kph or 50 mph. I'll revise in the final draft.

The 99 manual verifies these numbers except it shows the 212 values as 221. I verified the 212 is the correct value.

[jba3]

Wow, that's very interesting. Do you have any idea if this would be affected if you had two driver's side fans installed? I still have both stock fans but bought another A/C fan to replace the passenger one plus it would free up more room too. I'm assuming that if it was wired up correctly it would make no difference. I will have to check into it though.

Do both fans have the same CFM rating? Must be some reason mitsu put a larger fan on one side, instead of making them all the same size.

[Greg E]

Do both fans have the same CFM rating? Must be some reason mitsu put a larger fan on one side, instead of making them all the same size.

I imagine the larger one flows more air since it has a high and low speed setting.

[Patryn]

Either way the two driver fans are enough to keep engine cooled, especially if they come on sooner and/or run at high speed. It helps control heat soak especially in summer. Greg, thanks for all the work you have been putting into these ECU's.

[TurboSinceBirth]

Do both fans have the same CFM rating? Must be some reason mitsu put a larger fan on one side, instead of making them all the same size.

I don't know for sure all I know is that the OEM fans flow more cfm than any other fans on the market. Plenty of people have had no issues overheating switching to twin A/C fans. I plan to do it. Maybe it's just part of the factory shrouding but I do know they push quite a bit of air. The A/C fan will give me a little more room too.

[Toni]

I did this mod to my 1g. Works well! I did have some questions. What's with the -40 cells? Also, for the idle/slow speed settings they are both pretty high temps. Don't we want the fans to be kicking in early here since the car is not moving and there is no airflow?

Also, do we have target table of temps that we want to hit? Like x degrees at idle and cruise with and without the ac on? Obviously this depends on ambient temps and how hard we drive the car but generals are good.

Cruising and idle my car wouldn't go above 96C/205F with these new settings with AC on and 90F ambient.

[Greg E]

Mitsubishi intended for the fans to be on at all times with the AC on. Problem is in the winter when you are trying to warm your windows with the defrost they kick on and it takes longer for the coolant to get up to temp thus your car takes more time to warm up.

In the opposite direction, with out the AC on the other issue is with a FMIC your car over heats...

Part of me wants to eliminate the thermostat and target 170 deg to see if that helps with knock on pump gas.

[sergechronos]

Actually, small coincidence, was going to look it up and see what the Evos ran with FMIC. I set mine in the flash ECU (will be doing the actual flashing in the next day or two) about 10-15 degrees cooler, but wasn't sure if that was too much or not enough.. This pretty much did all the research for me. Thanks man.

[anyonebutme]

eliminate the thermostat.

requires welding........just in case you were thinking it could be done by just removing the stat, which it can't. FYI.

[Toni]

Part of me wants to eliminate the thermostat and target 170 deg to see if that helps with knock on pump gas.

Just had a thought. Would it be a good idea on the dyno to run all the fans full bore when doing pulls?

[Greg E]

Just had a thought. Would it be a good idea on the dyno to run all the fans full bore when doing pulls?

They will kick on when needed. Just like if you were sitting in traffic

[cjbyron]

Properly designed fans would cool effectively to set temps and not require earlier activation to work. A stock VR4 with properly maintained cooling system and proper shrouds in place works perfectly with the intended fan settings. If not, the problem is not when the fans come on but something else.

IOW - having them turn on earlier really isn't going to improve their effectiveness. And if it won't control or hold your engine temp as designed at 190-200 then it won't do any better coming on earlier. You have something else going on.

A lot of some people's overheating problem is using the FAL fans and removed shroud or other applicable panels. Added to this is corroded (scaled) radiator or block or both. I've seen so many chase an overheating problem only to look in their radiator to see huge scale built up all over it from 20 years of neglect. Replace the radiator in that instance and 'voila, engine temps back to WNL as designed.

I wouldn't want my V6 to run at 160F or fans to turn on then. That is way too cold for normal operating temperature on our engines. 170 is also too cold. You don't want your car to target that as your operating temp.

Also, some claiming overheating is not actually overheating at all but normal upper operating ranges. I don't know why some think that 200F or thereabouts is overheating for a twin turbo V6. That's not overheating. It's where it should be and nothing to worry about under normal conditions.

[Greg E]

I wouldn't want my V6 to run at 160F or fans to turn on then. That is way too cold for normal operating temperature on our engines. 170 is also too cold. You don't want your car to target that as your operating temp.

Why?? (Genuinely curious about this)

You're right about needing proper shrouds to keep air directed thru the cores, however,in my experience you'll still get over heating (my definition of over heating is 220degF) issues even with shrouds. The issue is caused when the IC itself becomes heat soaked (most people run poor quality inner coolers). In the past my fix for this was to turn on the AC and pull the AC clutch fuse so that the fans would kick on and draw more air thru the cores and cool them off faster. Now, it's no worry.

[cjbyron]

Because 160 is not the optimum temperature for the engine or even close. Too cold. Nothing mysterious on the why. I don't know if you are talking just about cars with a FMIC or stock or what. Either way, the normal operating temperature at which the tolerances and engine was designed for is in the 190Fs. I doubt you will ever keep the car in that 160 heat range anyway unless a really cold day out. At which time it would be a hindrance to drive around all the time so cold. But the point is that trying to maintain that cold (by turning on that fans so early) isn't going to gain anything. If it does anything it will be to overcool your engine below the proper operating temperature range. In the summer of course the engine will still probably override that low of a temp and only result in your fans running more often than they should.

If your car performs and holds steady at around 190-200 with your fans on all the time that's great. I just don't see where it is advantageous to have them come on at such a low temp. I think differently I guess - if your fans cannot keep the car at the right operating temps as it was designed (short of a lot of big mods) then I'd look at a different cause or fix rather than trying to reprogram the fans to catch up sooner. IOW - the cooling system is probably in poor condition. The fans should be able to control the temps as listed in the chart and then engine staying within the designed operating range(s).

As for the fix you mentioned by pulling a fuse - that is just going around the actual cause IMO. Not to mention what if you want AC on (because it is summertime and is when most cars complain about overheating).

These cars never had overheating problems from the factory for all the years they were sold and the factory kept the same settings without any problems. It was only when they started getting 20 years old, poorly maintained, and modded with cheap parts that it started being an issue. First step in overheated car IMO is to check for scale build up (likely) and also look at what is being run for coolant (too much antifreeze reduces cooling).

And as we both agree, get those radiator shrouds on there as well as the under car 'splash shield' which many cars do not have them on, especially the older ones that damaged the front AA and never replaced. All of those help direct the air properly and makes a tremendous difference in your cool system performance.

Now higher mod'd cars that truly need a FMIC (many don't) is a different story since putting out an appreciable higher level of hp (say 500+) changes the game plan on factory cooling system design. For this thread I though you were mainly talking about stock or a little bit above like a few bolt on mods and under the 500ish range or racing applications. I maintain that the cooling system should match the engine needs not have to come on 30+ degrees colder than you want to maintain as your target operating temp. Yah know? Even on my race car I have the #1 fan set to wait until 185F until it comes on. Target temp is 192-198 which is just right IMO.

Nice to have a little more control over the fans on/off no doubt. I just wouldn't look to that feature to work miracles in most overheating problems or plan for a 160 or 170 target temp as being a good plan.

[sergechronos]

Mitsubishi intended for the fans to be on at all times with the AC on. Problem is in the winter when you are trying to warm your windows with the defrost they kick on and it takes longer for the coolant to get up to temp thus your car takes more time to warm up.

In the opposite direction, with out the AC on the other issue is with a FMIC your car over heats...

Part of me wants to eliminate the thermostat and target 170 deg to see if that helps with knock on pump gas.

Believe all that you would see is that the car would take longer to warm up. Setting the fans to a lower temperature or increasing the surface area for the radiator would do more to keep temperatures down than changing or removing the thermostat.

[Greg E]

Because 160 is not the optimum temperature for the engine or even close. Too cold. Nothing mysterious on the why. I don't know if you are talking just about cars with a FMIC or stock or what. Either way, the normal operating temperature at which the tolerances and engine was designed for is in the 190Fs. I doubt you will ever keep the car in that 160 heat range anyway unless a really cold day out. At which time it would be a hindrance to drive around all the time so cold. But the point is that trying to maintain that cold (by turning on that fans so early) isn't going to gain anything. If it does anything it will be to overcool your engine below the proper operating temperature range. In the summer of course the engine will still probably override that low of a temp and only result in your fans running more often than they should.

If your car performs and holds steady at around 190-200 with your fans on all the time that's great. I just don't see where it is advantageous to have them come on at such a low temp. I think differently I guess - if your fans cannot keep the car at the right operating temps as it was designed (short of a lot of big mods) then I'd look at a different cause or fix rather than trying to reprogram the fans to catch up sooner. IOW - the cooling system is probably in poor condition. The fans should be able to control the temps as listed in the chart and then engine staying within the designed operating range(s).

As for the fix you mentioned by pulling a fuse - that is just going around the actual cause IMO. Not to mention what if you want AC on (because it is summertime and is when most cars complain about overheating).

These cars never had overheating problems from the factory for all the years they were sold and the factory kept the same settings without any problems. It was only when they started getting 20 years old, poorly maintained, and modded with cheap parts that it started being an issue. First step in overheated car IMO is to check for scale build up (likely) and also look at what is being run for coolant (too much antifreeze reduces cooling).

And as we both agree, get those radiator shrouds on there as well as the under car 'splash shield' which many cars do not have them on, especially the older ones that damaged the front AA and never replaced. All of those help direct the air properly and makes a tremendous difference in your cool system performance.

Now higher mod'd cars that truly need a FMIC (many don't) is a different story since putting out an appreciable higher level of hp (say 500+) changes the game plan on factory cooling system design. For this thread I though you were mainly talking about stock or a little bit above like a few bolt on mods and under the 500ish range or racing applications. I maintain that the cooling system should match the engine needs not have to come on 30+ degrees colder than you want to maintain as your target operating temp. Yah know? Even on my race car I have the #1 fan set to wait until 185F until it comes on. Target temp is 192-198 which is just right IMO.

Nice to have a little more control over the fans on/off no doubt. I just wouldn't look to that feature to work miracles in most overheating problems or plan for a 160 or 170 target temp as being a good plan.

I just read a bunch of opinions... None of which answer my question. Why is it so bad to run an engine cool?


BTW I already know that with the thermostat eliminated the engine still gets up to temp.

When i get a phone call from someone on a cruise on a hot day and their car over heats, guess what I tell them to do? A lecture about the necessity of a FMIC isn't going to get them off the side of the road.

It's probably worth mentioning that I don't run FMICs on my personal cars. Many people feel the need to so as such I'm presenting an option to work around the hole they dig themselves into.

[Greg E]

Believe all that you would see is that the car would take longer to warm up. Setting the fans to a lower temperature or increasing the surface area for the radiator would do more to keep temperatures down than changing or removing the thermostat.

Yes people tell me this happens a lot with a quality aluminum radiator. I'm simply curious what the draw backs would be to running our engine so cool. Does it have to do with keeping the oil temps up?

[sergechronos]

In theory, even the best radiator on earth shouldn't impact warm up temps too much until you reach the point that the thermostat starts to open.

Hmm..I would imagine that cooler temps could potentially increase wear, potentially things could be kept from reaching temps capable of expanding to proper clearances? Potentially worse fuel economy (although nobody drives a VR4 for the gas mileage). Hard to say for sure, there would be a variety of factors to testing it all out and accounting for variables to determine long term impacts of it. I would venture that it's probably a relatively minescule difference and could be tuned for anyhow, the heater not being as effective aside. Anything that triggers off of coolant temps would need adjusting.

I am on both sides of this as I did lower fan settings for now, but I will probably put them back close to the original settings as time goes on. For folks running a front mount, the fan control can help for sure, but a coolant system flush, replaced with around a 70% distilled water to 30% coolant mix and/or water wetter would go a long ways, especially with a higher pressure radiator cap. But, I digress from the point. Impaired heater function and gas mileage are for sure issues with it, with the possibility of increased wear. Again though, that last one would need testing to back it up.

[cjbyron]

Well, what temp would you want to run your car at? How about 100F? 120? Do you WOT at 125F? Where is the optimum and best operating temp at? I say 192 (yes, that is my opinion). Seemingly this also matches what the factory settings are targeting or real close to it. The why is easy as already stated - the engine is designed to run at a certain temperature for obvious reasons. If not then why not have the fans on continuously and try to run the thing as cold as possible. Do you also go WOT before your engine has warmed up? The concept here is very simple.

Plus as someone else already mentioned - unless you've pulled your thermostat it isn't even going to open until above 170 so having your fans running to the radiator at 160 will not do anything since the thermostat is still closed.

I didn't know we were talking about an answer to someone that phones you to help them on a hot day with their car. I thought this was on a forum where other input and suggestions (or opinions) were part of the routine. As for an option to work around I think that looking at their cooling system health and removing scaled up radiator, putting shrouds back on, etc. is certainly a simpler and easier obtained answer than reprogramming the ECU. And even if so should still be looked at rather than working around with such 'fixes'.

That tis all

[Greg E]

In theory, even the best radiator on earth shouldn't impact warm up temps too much until you reach the point that the thermostat starts to open.

Hmm..I would imagine that cooler temps could potentially increase wear, potentially things could be kept from reaching temps capable of expanding to proper clearances? Potentially worse fuel economy (although nobody drives a VR4 for the gas mileage). Hard to say for sure, there would be a variety of factors to testing it all out and accounting for variables to determine long term impacts of it. I would venture that it's probably a relatively minescule difference and could be tuned for anyhow, the heater not being as effective aside. Anything that triggers off of coolant temps would need adjusting.

I am on both sides of this as I did lower fan settings for now, but I will probably put them back close to the original settings as time goes on. For folks running a front mount, the fan control can help for sure, but a coolant system flush, replaced with around a 70% distilled water to 30% coolant mix and/or water wetter would go a long ways, especially with a higher pressure radiator cap. But, I digress from the point. Impaired heater function and gas mileage are for sure issues with it, with the possibility of increased wear. Again though, that last one would need testing to back it up.

The reason the thought is rolling around in my head is a theory that cooler temps will draw more heat from the spark plug & combustion chamber and thus help reduce knock. It's just an idea I would like to test.

Gas mileage isn't any concern as all you do is scale back the warm up enrichment percent table.

[Greg E]

Well, what temp would you want to run your car at? How about 100F? 120? Do you WOT at 125F? Where is the optimum and best operating temp at? I say 192 (yes, that is my opinion). Seemingly this also matches what the factory settings are targeting or real close to it. The why is easy as already stated - the engine is designed to run at a certain temperature for obvious reasons. If not then why not have the fans on continuously and try to run the thing as cold as possible. Do you also go WOT before your engine has warmed up? The concept here is very simple.

Plus as someone else already mentioned - unless you've pulled your thermostat it isn't even going to open until above 170 so having your fans running to the radiator at 160 will not do anything since the thermostat is still closed.

I didn't know we were talking about an answer to someone that phones you to help them on a hot day with their car. I thought this was on a forum where other input and suggestions (or opinions) were part of the routine. As for an option to work around I think that looking at their cooling system health and removing scaled up radiator, putting shrouds back on, etc. is certainly a simpler and easier obtained answer than reprogramming the ECU. And even if so should still be looked at rather than working around with such 'fixes'.

That tis all

You really don't have anything useful to add to this conversation do you?

[cjbyron]

Other than common sense? No, not really.
Not sure why you have your panties all in a wad. It was nothing more than that (common sense).
It isn't like the gasoline combustion engine is new or that somehow you know better than the factory engineers.
Why you think otherwise is beyond me. Certainly no reason to become adversarial about it.
But by all means, please continue.

[Greg E]

Other than common sense? No, not really.
Not sure why you have your panties all in a wad. It was nothing more than that (common sense).
Why you think otherwise is beyond me. But by all means, please continue.

Yeah that's what I thought.

[Greg E]

truly reverse engineering marvel.

Why thank you! :D

[cjbyron]

You're welcome! :)

[R/T93]

Drag racers run as cool as possible with their coolant but generally like motor oil up to temp. BTW they make oils that are good @ 130 deg F now. So if 130F is "up to temp" for you you're golden.

Look at any drive-along video with Tom Nelson. He puts beast mode cooling systems on his cars so cruising around temps are in the 150-170 range. A couple 3rd gear single block burnouts later the temps have hardly moved.

CAUTION- OPINION FOLLOWS
My car seems to have more 'pep' before the oil gauge registers 50C. I like to leave my car off as long as possible for my first auto-x run and hopefully by the starting line staging area I am < 60 deg C And no I am not wearing out my engine finding this out, either. 50k of oil analysis has shown that to be true.

However if you are trying to get 300k out of your 98 4 door LX Civic maybe you should just trust the MFR temp ratings and let it be.

[Greg E]

What odd is all the other mitsu ROMs out there have the fans come on at lower temps. Even the turbo eclipse.

I wonder if you're right Nate and oil temperature is the reason Mitsubishi wanted this motor to run in the 200deg range. .

[sergechronos]

Well..Would've guessed maybe the clearances on the bottom end or the oil cooler thermostat perhaps, but factory clearances aren't much different than that of a DSM and I doubt that they would leave the fans so high just due to a thermostat for the oil cooler. Honestly, the only thing I can think of is perhaps they figured with the sidemounts ICs keeping heatsoak away from the radiator that they didn't need the fans to come on so soon?

Or, maybe they just came in drunk that day..Let's be honest, there's a few things that they did that just didn't quite make sense.

[cjbyron]

I think it might be more accurate or realistic to compare other V6 TT engines and not the brand (Mitsubishi). Comparing our V6 to a 4 cylinder is kinda apples and oranges. If we go the other way and compare to V8 engines we'll find the target being 210-220 as the normal operating target temp. My Toyota FJCruiser has a V6 engine and also is in the same temp ranges of 190-200 like the Mitsubishi V6. I suspect other V6s will also show to be in the same temperature ranges. My 6.2L V8 Yukon however is right at 212 where GM wants it to be.

Yes there are other applications such as pro drag and other specialty engines that run cooler but they are also designed that way from the start. The majority of people here having an overheating problem are still running stock engines mostly or darn close to it on the bottom end. So I was sticking to that as the parameters. Many drag racers also like their engine oil hot, but is still subjective. In the end are we talking about drag racing and performance or the average 3S user that wants to DD and change up their fan temps for some reason (overheating)?

So maybe it'd be better to compare V6s in general and see if the VR4 is the anomaly or if it is right in the same ballpark as other company's V6 designs and specifications? I don't think they (car mfg's) would all be wrong in their target temperatures. I am willing to bet they will all be in the 190-200 range.

[sergechronos]

Hmm..Well Nissan Frontier V6 (NA) was around 180-190 regular.
300ZX regular operating temp is...180ish as well I think. Been a while since I've been around one, and the one I was riding it was NA, not TT.
V6 Passat is around 190 as I recall as well.