low oil pressure at idle when engine temp is normal

I just started having this issue. First I noticed this when I got caught in a McDonald's drive through line up that was very slow. I noticed that while waiting the engine temp gauge started creeping up. It hit 100 well above the normal 80-90 mark and kept climbing until it flashed a warning and I turned off the engine. I had to move the car again while in line and I started it up like approx 60 seconds later and it was down to 100 mark. I turned the engine off and on again through the line up and temp went down some more but my battery wasn't going to be able to start it again so had to keep the engine on. I noticed that while I drove just a short distance in line up that the temps went down. I got to the drive through window and temps started climbing as I idled again while I paid. I drove off and and temps immediately started dropping again really quickly by the time I parked in the lot the temps were in the normal range. I drove home, temp was normal and I parked and let it idle, I notice I get a low oil pressure warning which goes away right away. Temp started climbing again, I let it get to near 100 and then I raise the rpm to 1500-2000 and see oil pressure go up and temp starts going down and I tried this multiple time and it does the same thing. Next day under cold start up the oil pressure in around 5 bar when idling and driving. Stays that way until it warms up to normal then temp is normal while driving but when I stop I get low pressure warning and the temp starts going up the longer it idles.If I raise rpm over idle rpm the temp doesn't go up or drops to normal. Any idea what is causing the issue?

Are your radiator fans working? Cooler radiators=cooler coolant=oil temperature and pressure better.

OP - Like Joe asked, do you hear your fans running? They should run when a/c is on. If you have a Durametric, you can turn on high and low speed fans any time. If even one side fan fails you can have water temp creep up. After engine gets to normal temp, what is your idle oil pressure? What oil and how long has it been in the engine?

I hear fans in front and rear lid kick on once temp is just above normal. My idle oil pressure is 1 bar and slightly under 1 bar while hot. Rev it just a bit and oil pressure goes up and drops down again where I may get the low oil pressure warning light come on but goes off by itself. Oil is fresh 5w-40

Engine is getting too hot and thins the oil out. Find out why it's getting too hot and the oil pressure issue should go away.

Could be water pump, air in your system, low coolant, or thermostat issue. On my �99, the engine coolant temp doesn�t change very quickly with respect to airflow (due to high speed driving on having the fans on). It takes 1-2 mins for a big change in airflow to be reflected in the ECU or dash gauge.

Also, after you fix the potential issue, if you are still getting a low oil pressure warning at idle and your water temps are ok (I�d say 100C is fine), you might want to switch to a 5w-50 oil. The higher viscosity should give you at least 1/4-bar improvement in oil pressure.

I warmed up the engine today with the coolant cap off. After the car was warmed up to temp I put the coolant cap back on. Oil pressure was 1.1 bar at idle (700 rpm) and no low oil pressure warnings after revving the engine to 3500 and letting it drop back to idle Maybe it was just air in the system. I did have a coolant cap issue that was leaking and had to top up the fluid and replace the cap. So maybe air got in at that time. Im hopping that was the problem but well see the next good weather day that I can take it out for a drive.

Best to check coolant level before you drive the car next time to make sure level is OK. Perhaps drive it with the wire on the black cap UP to purge remaining air (@ higher revs than idling). If the symptoms remain, perhaps the water pump impeller has more than a single damaged vane thus greatly reducing the flow at idle rpm.

Quotes source post: 17721204

Putting higher than required viscosity oil will only mask the problem, it won't fix it. Used car dealers do this to sell cars with worn out engines. Find the cause and fix it.

Quotes source post: 17720615

I see that you say in a later post the temp keeps increasing to 100, even with fans, and that you seem to have got it fixed with the coolant cap off. Interesting, I'll add this to my troubleshooting list. But if it isn't solved, here is what I have found. If temperature is within normal range, but on the high end (hot idle), and oil pressure goes below 1 bar. There are MANY threads out there with people discussing the problem, but no one ever posts what they did to fix it, with one exception. Unfortunately, there are only a couple things you can do since you said fans are working. First confirm that your pressure really is low using a mechanical gauge. It is a pain to do, but is the only way to confirm that you have low pressure. If you actually do have low oil pressure, this is all that I have been able to find on the problem: 1) worst case scenario, the main bearings are worn causing pressure loss and that is apparently an engine rebuild. 2) could be the oil pump gears are worn and toast. I've seen posts on this in the 986 section 3) an internal seal somewhere is leaking - engine teardown 4) bad sender - but this would show erratic behavior, not low oil pressure. Cheap fix, but need to confirm using a mechanical guage. 5) chain tensioners or maybe chain guides are worn - chain tensioners are not so bad to replace, but chain guides require engine disassembly 6) oil uptake is clogged - drop the oil pan and remove debris from oil uptake filter. Now need to find out where the debris came from - engine teardown likely Engine teardown is an expensive way to go, but this is where the rabbit hole goes. 5w50 is an oil that is acceptable for our cars, so no problems using that. I switched to 50 and indeed did get better oil pressure. I also installed manual fan switches, even though temps were within normal. See here: https://rennlist.com/forums/996-foru...ling-fans.html

I'll add one more thing to the list - have you ever cleaned out your radiators? A lot of stuff builds up between the radiator and condenser and air can't move through.