Oil Pressure Drop and Stalling

Greetings all,



I recently purchased a 1990 3.0L 4x4 and had to get some engine work done. One of the cylinders had absolutely no compression, and being that I have limited tools and no repair manual, I had my mechanic take things apart and fix it up. For the past three months, everything has run great.



Yesterday morning, I drove to the store. The truck ran fine. After about 20 minutes in the store, when I came out and started it up, the oil pressure was really low (all the way to the left), the idle RPM was barely 500 (normally it is around 2000) and slowly it started dropping until the engine stalled. I started it again, and the same thing. Finally, I had to start the engine and rev it to keep it going.



Every time I came to a red light, the oil pressure gauge would drop down and the engine would start sputtering until I revved it. I nursed the truck back home. After the engine cooled a bit, I checked the oil level and it seems fine. I couldn't find a leak anywhere. The truck has not done the same behavior today.



Was this a fluke or the start of a problem that I need to address before it turns into something big?



Thank you!

Reply 1 : Oil Pressure Drop and Stalling

Do you have a coolant loss? Have you tried to adjust the idle to 800 (not 2,000) rpm? At 500 rpm you are going to have very little oil pressure and the engine will not stay running for long.

Reply 2 : Oil Pressure Drop and Stalling

Thanks for replying so quickly.



As a matter of fact, there seems to be a slight coolant loss somewhere in the system. There is no puddle anywhere, but the reservoir slowly depletes. What does that mean then in relation to the oil pressure?



I have not tried adjusting the idle down. I will need to try that. I need to get myself a Haynes manual for this truck.



My first car was an 84 Toyota Tercel 4WD Wagon...I used to do all the work on that...but it finally needed more money than made sense, so I sold it off a long time ago.



Thank you!

Reply 3 : Oil Pressure Drop and Stalling

Longbed is right get the idle to 800rpm like it should be.



Not sure why the coolant would effect the oil pressure. DO you have a pressure gauge or just the caution light?



I ask cause my caution light will come on in my other car but I know the sensor is bad cause the actual pressure gauge reads ok.



I doubt it will work on these trucks but on newer cars when I throw a code or dummy light I try resetting the ECU but disconnecting the battery. Once again I do not know if you can do that in these trucks.

Reply 4 : Oil Pressure Drop and Stalling

No warning lights...the oil pressure gauge reading drops, though I am not sure how reliable that gauge is. But, the drop in pressure did correlate with the stalling, so I suspect something is going on, I just don't know what.



Maybe it was some type of fluke. I read about blockages on other threads, so maybe something got stuck and now is fine.

Reply 5 : Oil Pressure Drop and Stalling

Do you get any white smoke out the exhaust when this occurs? If so, you have a blown head gasket. The slowly disappearing coolant is a dead giveaway. I woukd return to your mechanic & find out what exactly was done before.

Reply 6 : Oil Pressure Drop and Stalling

the oil pressure dropping is not going to in any way cause the engine to stall unless it siezes up. toyotas run very low oil pressure at idle under normal warm conditions (spec is 4 psi at idle from the factory). that's 800 rpm. at 500 it'll be even lower. IMO the oil pressure is a symptom of the low idle, not the cause. I know my truck doesn't pull enough air to open the AFM and keep the fuel pump running at 500 rpm. Find out why you're idling so low and you'll solve the other problems. Google the 93 pickup FSM and find the troubleshooting tree for low idle.

Reply 7 : Oil Pressure Drop and Stalling

It finally did it again, and this time I looked for white smoke or any other symptoms that were mentioned, but there was nothing. The idle was around 500-700 at the time of the low pressure, but this time it didn't sputter. The only correlation I could determine was that I was starting the truck while it was still warm after it sat for about 15-20 minutes.



Thanks for the heads up on the FSM. I wasn't sure if the 93 one applied to the 90 truck.



Now to do more research!

Reply 8 : Oil Pressure Drop and Stalling

Quote:

Originally Posted by kamesama980 toyotas run very low oil pressure at idle under normal warm conditions (spec is 4 psi at idle from the factory). that's 800 rpm.

That's good information to know.

Reply 9 : Oil Pressure Drop and Stalling

Quote:

Originally Posted by MasterDDS It finally did it again, and this time I looked for white smoke or any other symptoms that were mentioned, but there was nothing. The idle was around 500-700 at the time of the low pressure, but this time it didn't sputter. Thanks for the heads up on the FSM. Now to do more research!