Culpeper

1990 V6 4runner

Motor runs fine except when I take off the oil cap on the valve cover and then the idle drops way down. Screw the cap back on the idle returns to normal.

GregStevens

No, that's not compression loss...that's loss of oil pressure.

You loose compression by, among other reasons, by having a bad head gasket, bad rings, etc. Oil pressure isn't related to compression, per se. But when you take the oil cap off, the engine loses oil pressure...not a good thing to do, but won't hurt anything that I'm aware of unless you leave it off for some reason for a long period of time.

Culpeper

Thanks. I was afraid that at least something like a valve adjustment was in order.

arkieoscar

Just where is the oil pressure going? It's more likely the extra air into the intake through the PCV system leaning the mixture at idle. If the oil pressure is dropping from the oil cap being off, there is something strange going on.

nunsa

This is normal, nothing to do with your oil pressure! Don't be fooled!
There's nothing wrong with your 3.0, no harm, no foul! The engines of today are closed systems, unlike the systems of yore whereas the pcv valve vented down into the air. If you pull your pcv valve your idle will also change the same way!
Good Luck!

Culpeper

Semper Fi!

GregStevens

I forgot to put the oil cap back once after putting some oil in and drove across the parking lot before I realized it. It was running horribly...and the first thing I thought of was loss of oil pressure. And that's why posted the above. Whoops...

Try this. Remove the oil cap and observe.

Then disconnect the PCV tube that goes into the intake and see if the same thing happens.

I had assumed that it was loss of oil pressure...but that's crankcase pressure and not in the heads. So I'm thinking the loss of the PCV vacuum is causing the problem, not a drop in oil pressure...sorry for the brain cramp.

But a loss of compression ONLY takes when compression is lost within a cylinder...through a bad head gasket or bad rings or perhaps a loose spark plug. Compression only takes place inside each cylinder...and would not be effected by the PCV vacuum loss.

nunsa

OOHRAH!

Culpeper

Thanks. I check all that out tomorrow.

Speaking of oil pressure. My 3.0 doesn't seem to need a lot of it. Idle the gauge is on the first mark. While driving depending on the RPMs it is between halfway and on the third mark. Just like in the owners manual. Only my motor has 137000 miles. I suppose this is normal. Oil consumption is about 1 quart between oil changes (about every 3000 miles). Motor has no external oil leaks. As for head gaskets. They were replaced by the previous owner a long time ago. I'm the second owner. It is entirely stock and has only been serviced through Toyota dealership. The maintenance records from Toyota go back ten years. After that I have a list of maintenance dates and invoice description because the computer system at the dealer purges after ten years. I'm not bragging just love my 4runner.

Nevertheless, there is one thing I am concerned about where the motor is concerned. Holding down the brakes, in Drive, and give it some gas and I hear what I think is bearing noise. vrump vrump vrump. I don't hear this when the motor is cold. Just after it is warmed up. I can also hear this when driving below 5 mph.

nunsa

That's good Oil pressure for the 3.0, most 3.0 will run on the low side where oil pressure is concerned, comes with the payments!
This noise you described: vrump,vrump! Is it coming from the engine?
Vrump: Idler bearing, water pump..? Explain a little better please!
G/L! S/F!

Culpeper

I'm thinking it is a rod bearing. It only occurs when under load and low RPMs. The noise is coming through the exhaust. Or at least it's resonating through the exhaust. Ever heard an old 1971 Ford LTD when driving slow? That is what this 4runner sounds like only not as bad.

nunsa

That's not good! I'll tell you what, before my 3.0 HG started to leak I didn't burn so much as a pint of oil between oil changes and even after the rebuild I still don't! Anyhow back to your problem, If it's a rod bearing it would make sense that it only does it when warm, reason being is that when cold the oil is thicker closing the gaps and when she warms up the gaps open up and you hear it! Time for a rebuild my man, if your going to do it do it right like I did with all the goodies!
G/L & S/F!

Culpeper

I agree. The noise isn't getting any worse over time though. The last time I had the oil changed I asked the service tech to make sure the mechanics checked for any unusual bearings noises and he came back and said there wasn't any. I'm going to ask the same thing again next time only I'm going to be more specific.

nunsa

If it's not gettin worse it could be somthing else, agreed?
A rod bearing will get worse, matter of fact any bearing will get worse!
It could be something else? Fan clutch, idler bearing, WP, too heavy an oil..!

Culpeper

Yeah, I edited my reply above with a little more information. Bottom line is the motor is old and has some miles on it. Because it's a Toyota I would hate digging into the motor unless it blows up. I have an 82 Celica with 225000+ miles on it. It has some issues but is still dependable. Not worth digging into. I would drive it almost anywhere and anytime. Nevertheless, the next oil change I'll get the Toyota techs to check it out better. Better to know exactly what it is than wait around until I get stuck between Roswell and Vaughn in the middle of summer. I have no desire to dust off my tactical survival skills if I can help it.

I just took a trip with the 4runner and drove it about a thousand miles, mostly highway, and the noise hasn't become worse.

nunsa

I had almost 300,000 original miles on mine before the HG started to leak!
Stay away from the "stealerships" the labor rates are through the roof! Find yourself a good independent garage! I worked at a "Stealership" for 6 years, so I know! I have 305,000 miles on my truck now with 8000 on the rebuilt 3.0 I did!
The Toyota engines keep on going and going and going.....!
Try a different oil, Valvoline, Castrol, Amsoil....!
It could make a diff. especially if you use crap oil!

Culpeper

Will do! Especially the oil. I will update this thread has I found out more.

Culpeper

Toyota states again there is nothing wrong with the motor. Just exhaust noise.