Oil Weight vs Oil Pressure Issues

[DrGonzo]

I have been noticing some issue with my oil pressure lately and wondered if it had anything to due with the weight or brand I was using. Currently running Rotella T5 which is a synth 15w-40. When I first start the car up the oil pressure is nice and strong "60-70psi cold" after warm up it is about 15-20psi at about 750 rpm's idle. After some around the town driving I noticed the pressure almost bottoming out after the engine is fully hot 190-200F The oil has thinned out a lot. I don't recall having this problem with the T6 Full Synth Blend.

I am wondering do I need to switch to a different weight/brand?!?!

Any Suggestions?!?!?

[MR2]

I suggest try something else and let us know what happens..

check the oil you drain to check for serious shiney problems

I assume it's not the filter or some other odd weird other thing.

[DrGonzo]

So what would be a better/heavier oil to switch to??

Going to be changing the oil in the next week or so. Sending it off to Blackstone for analysis. Should be fine as I just checked the bearings in the last two months and I barely drive the car. I don't even know what filter I'm running. Might be a Mobil1.

[Gamerse]

Did you replace your oil pump during your rebuild? I had a similar issue on my recently swapped 60k engine. Turns out I had two contributing factors, contaminated oil from working out a no-start condition, and not knowing the condition of my current sending unit. I'm guessing you are watching a mechanical gauge since you are calling out numbers. The dummy light comes on at 5 psi, as long as it is not on or flickering, all is well. You only need 5lbs of oil pressure per every 1000 rpm to sustain lubrication. This is the reason the light is set to 5psi.

I changed to 15W50 synthetic mobile from contaminated castrol GTX 10W30. The conditions are still temperate here, and the FSM recommends 20W40 for current weather conditions. The 15W50 also had the highest VI of all the oils I had to choose from at the local autozone. Pressure "appears" to have risen. I can't say how much, but the factory gauge is in a more confident position, and my baseline does not drop when hot. My original engine ran Rotella full syn 5W40 (was the only full syn rotella availible) . That engine's pressure was ideal for factory gauge. It stayed slightly lower than center, and stayed centered during normal driving. I miss that 150,000 mile engine. (idler pulley killed it) Weight usually has a more dramatic affect on loose engines (think 350 chevy ect) or engines with loose oil pumps. Filter should have absolutely no bearing on oil pressure. If it does, it was clogged and the bypass was open. Hope you figure something out. good luck

I'm going to install a mechanical for diagnostics

[a2j]

I use 10w40. my pressure is 40psi warm idle. 60-90psi easy/hard driving. is this normal? I'm unable to find what is normal for stock engine.

[mb3000]

Subscribed. Need to change out my 20W before it gets cold!

[DrGonzo]

I use 10w40. my pressure is 40psi warm idle. 60-90psi easy/hard driving. is this normal? I'm unable to find what is normal for stock engine.

What brand oil are you using??

My pressure readings are about the same but once the engine gets warmed up and runs for a bit my pressure numbers plummet!

[a2j]

I use Castrol non-synthetic.

[Gamerse]

I can't find any specs in the manuals, but in general, oil pump manufacturers set relief springs to 60psi. Here are some FSM pages. I haven't looked to see if the spring is accessible, or if it behind the oil pan somewhere. I really didn't pay much attention to mine when I put my new pan on, other than it was clean and there were no cracks in it.

[Gamerse]

Maybe the spring has failed and is opening after it heats up.