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Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4905
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I rebuilt a Toyota 4Runner 2.7 4 cylinder engine and I'm

Customer Question

I rebuilt a Toyota 4Runner 2.7 4 cylinder engine and I'm having low oil pressure problems.
Submitted: 10 months ago.
Category: Toyota
Expert:  Toyota Service replied 10 months ago.

Hello. Welcome to Just Answer. Please allow me to assist you. Are you relying on the oil pressure light as an indicator of low oil pressure, or, have you attached a mechanical gauge? Thanks

Customer: replied 10 months ago.
I attached a mechanical guage.
Expert:  Toyota Service replied 10 months ago.

The most common issue with low oil pressure after a rebuild is incorrectly sized main bearings. If your mains are incorrect, you allow oil pressure to escape past the crank oil lube orifices past the bearing clearances. This causes a drop in oil pressure as the bearing are what keeps the pressure up. Are you certain that the mains are of the correct size/did you plasti-gauge the bearings to see if you are correct with your bearing choice?

Customer: replied 10 months ago.
i used plastic-guage and bearings are within specification.
Expert:  Toyota Service replied 10 months ago.

Ok. I have experienced several oil pressure related issues in the shop; I cannot tell you which you have, but, if this vehicle was in my shop, this is what I would be checking:

1) Crack on the oil pickup tube (this causes the pump to suck air, not oil)

2) Gap where the pickup tube meets. If there is any clearance here, the pumps will suck air. I have had a tube once that would not fit perfectly.

3) Oil pump pressure relief valve stuck or faulty (this is common on 'sludged' engines)

4) Rare, but I have seen restrictions (from sludge) in the sump pickup tube.

5) Also rare, but possible on a high mileage engine is excess clearance in the oil pump gears.

Expert:  Toyota Service replied 10 months ago.

I assume the oilpump is new. We would not rebuild an engine with the original pump. Perhaps your new pump is machined incorrectly or has excess clearance.

Expert:  Toyota Service replied 10 months ago.

Also, make sure you have a Toyota oil filter on this engine. AC filters do weird things

Customer: replied 10 months ago.
Oil pump is new. When the engine is cold oil pressure is about 55 psi at idle. As it warms up the oil pressure gradually decreases to below 10 psi. at operating temperature at idle. At 2500 rpm the oil pressure is about 40 psi when engine is at operating temperature.
Expert:  Toyota Service replied 10 months ago.

Oil pressure at 55 psi/cold is OK. 10 PSI is rather low at warm idle. 40 PSI at 2500 RPM is OK. I suspect you need to get another oil pump.

Expert:  Toyota Service replied 10 months ago.

If all of your bearing clearances are good, you have no issues with the tube or the fit of the tube, I cannot see where you are dumping pressure. The cams wont dump a lot of pressure while they are in place. I suspect the pump is not developing proper pressure at idle.

Expert:  Toyota Service replied 10 months ago.

I assume that you are not using synthetic oil too.

Customer: replied 10 months ago.
I'm using synthetic oil 10W30.
Expert:  Toyota Service replied 10 months ago.

Synthetic oil has a tendency to result in a lower pressure because of its chemical structure. Conventional molecules are kind of "globby"; whereas synthetic oil is very structured. Before you consider pump back off, why not try conventional 10w-30, or, if the block was not bored and the crank not machined, 20-W40.

Expert:  Toyota Service replied 10 months ago.

I would not recommend synthetic oil in this engine. There is absolutely no benefit. The only reason synthetic is almost mandatory these days is because conventional oil does not have stable enough molecularity to be used as a pressure fluid. This pressure fluid (oil) is what causes variable valve timing to occur on the newer engines. Conventional oil does not move fast enough or with sufficient predictable volume at differing stages of temperature. With that in mind, the oil pump is not designed for a thinner type of oil that synthetic 10W30 is. I would use conventional oil and retest.

Customer: replied 10 months ago.
Ok I'll try that and see what happens. Can I continue on this same thread when I get though or due i need to start a new chat. This won't be until aroiund the 30th.
Expert:  Toyota Service replied 10 months ago.

We can stay on this thread; no need for a new chat window; that might get you one of my colleagues who is not familiar with your issue.