Hot idle oil pressure concerns
 

So I have some oil pressure concerns for my new motor. I have noticed it is always really high when the motor is cold. Once it warms up it starts to come down. Cold it will max out my oil pressure gauge at 99 psi. Once warm I cruise around 50-60 psi. Idle gradually gets lower as it gets hotter. At 160 degrees is around 17 psi at 750 rpm, 180 goes to 15 psi, over 200 gets down to 6 or 7 (haven't got it much hotter). I don't hear any noises at the lower oil pressures, but it is definitely concerning. Once I get the RPMs up the oil pressure gets back up to 50 or so hot.

The rod bearing clearances were on the tight side of .0020. The machine shop installed new cam bearings but I am reading loose cam bearings would cause low oil pressure at idle once warm.

The first oil change had quite a bit of metal sparkles (as expected) but the subsequent oil changes haven't had any metal, just very dark.

I had leaky intake gaskets for the first 2000 miles sucking oil into the intake ports, but that has been fixed.

I am currently running 5w30 synthetic Castrol in the hot Texas heat, but am going to do an oil change this weekend and thinking of trying a 10w40 and see if that will bring up the hot idle oil pressure. Does that seem like a good idea? Usually I see people recommending this for older motors, not new ones with potential cam bearing clearance issues. I am worried with my tight rod bearings the 40 weight may have problems slipping through.

I am going to get a manual gauge on it this weekend and see what that says.

Here's a pretty good thread for my build.
https://www.thirdgen.org/forums/tech...heads-dcr.html

Re: Hot idle oil pressure concerns
 

I just spent about 2 hours reading your entire build threads.
Yes, try the 10W40, but I don't think you should have had synthetic in the engine so soon. Have you taken a look at a few spark plugs lately?
You said you used .001" extra clearance ACL rod bearings. What did your final RB clearances measure?
It is almost unbelievable how much oil can thin out when it gets hot.
But I doubt your low oil pressure is from "loose" cam bearings.
Cut your oil filter open and inspect. Metal sparkles are never good.

Re: Hot idle oil pressure concerns
 

That's my first suggestion also. Replace the oil filter and cut it open. Take out a chunk of filter material and squeeze it in a vise to get the oil out of it then open it up for inspection. Things like bad crank and cam bearings will not cause a noise unless they get too hot and seize up but they will start to shed metal that can be easily seen in the filter.

Re: Hot idle oil pressure concerns
 

I should mention, I believe the oil pressure has always been low at hot idle. The sparkles were only in the first "break in" oil, which was just a few minutes of running. The subsequent 2 changes had no metal, just dark. I will try the 10w40, and cut open the filter.

Spark plugs have been oily the last few times they were pulled, i attributed it to the intake gasket leaking, which has since been replaced, but we shall see.

The rod bearing clearances were all between .0017 and .0020 after the oversized bearing swap.

Re: Hot idle oil pressure concerns
 

In my, albeit limited, experience, sludge stuck to the drain plug is okay on a new engine. Glitter isn't. You may want to investigate.

Re: Hot idle oil pressure concerns
 

Run a strong magnet through your drain oil.
It has been 3 or more oil changes so far, so if anything sticks, then you have trouble.

Re: Hot idle oil pressure concerns
 

Trouble with a magnet is that aluminum, brass, lead or any other non ferrous metal in bearings won't stick to it.

First oil change after a rebuild, ignore glitter in the oil unless there's big flakes. That's just the normal wear and tear of being broken in. If really in doubt, take an oil sample and have it analyzed. It can tell you if there's high concentration of metal that shouldn't be in your oil.

If there's no metal in the filter, then chances are the bearings are fine however it's always possible a cam bearing has spun causing hot oil, low pressures but generally that will show up in the filter.

Nothing wrong with using 10w40 oil. In the heat of summer, you could also use 20w50 but you'd want to change that out in the fall. I use 20w50 in my race car but it also never sees cold weather.

Re: Hot idle oil pressure concerns
 

Thats my thoughts exactly Alkyiroc, it wasn't flakes like glitter, looked more like fine metallic, I havent seen anything since. Everything I read stated the first oil change will have some metal (small flakes).

I just got in from changing the oil, and it looked pretty good, not all that dark really. No flakes at all, but I am going to cut the filter tonight. The 10w40 imediately jumped to 90 psi or so. After a short warmup (200 degrees) the idle psi dropped to high 30s, revved in the 60s. Too high imho but we will see after I drive it some this week.

Re: Hot idle oil pressure concerns
 

GM's rule of thumb is no less than 10PSI for each 1000rpms.

Re: Hot idle oil pressure concerns
 

Have you verified the hot idle reading with a mechanical gauge?
Don't put too much faith in the electronic gauge, especially if the car has an aftermarket sender. On another car I kept getting very low readings at hot idle from 3 (warranty replaced) BWD senders. A mechanical gauge showed that they were raising false alarms.
The original GM sender and 2 subsequent AC Delcos gave higher readings, and these proved to be more correct.

Re: Hot idle oil pressure concerns
 

Drain your oil through a paint strainer, O'Reilly's will probably give you a few then post pics of what you see in the strainer.
https://cimg8.ibsrv.net/gimg/www.thi...67b367424b.jpg

Re: Hot idle oil pressure concerns
 

:yup:


The gauge is more than likely reading off, especially if it's maxing it out when cold.


1st step is verify with a mechanical gauge.


Last time I had a car with the same kind of symptoms you're describing I ended up zip-tieing the gauge to a wiper arm so I could verify during driving conditions because just idleing to a warm engine was still seeing 10psi once warm, but driving around it would bottom out around 5 or less when coming to a stop. Did a complete teardown, everything looked fine i.e. nothing worn excessively. Did new cam and crank bearings and a new oil pump and all is good again.
Our assumption was that the oil pump pressure relief valve may have been sticking open once warm.