When driving my 3.0 4-runner at crusing speed (60mph) down the road I notice that the oil pressure increases by about 5psi when I let off the gas slightly then drops about 5psi when I give a little gas. Do you think this is a bad omen?? Any thoughts.

I have an aftermarket pressure gauge installed on my dash. That is how I know the accuracy.

If this has already been answered sorry. I searched and found nothing.

 

My OEM gauge always reads high when the motor is cold. The pressure will also read higher when the motor is spinning higher RPM's (foot on the gas), and very low at idle.

It has read this way with the 3.0 and now the 3.4 I have in there. Mind you, same sending unit and location is used for both motors.

I have heard that the OEM gauges are notoriously inaccurate though.

I realize this info doesn't answer your question directly, but you at least now know the pattern of another gauge is different from what yours is showing.

Whether this is bad or good... I am not sure.

 

oil pressure is a function of oil viscosity and engine speed.

higher oil temperatures = lower oil viscosity and resulting oil pressures.

higher engine speed = higher oil pressures.

When hot, look for around 10psi/1000 rpms. Anything less than that could be a problem. More than that usually isn't an issue.

HTH.

 

Sorry guess I didn't explain it well enough. All the info about viscosity and temp. I know. What I am experiencing is the oil pressure increasing as I am unloading the engine at highway speeds then it drops as I load the engine. For example, If I am going up a slight hill and I have to put a little more gas to it (not down shifting) the oil pressure drop about 5 psi, but then when I am going down the hill and let off the gas it rises about 5psi. Speed and RPM stay pretty much the same. It changes when I put on or take off a little bit of a load.

Hope this is a better explanation.

 

It was clear to me. Have you considered that the gauge or sending unit may be bad?

 

Thought about it. You wouldn't think so since it is new. However I have bought many things new that were bad.

What I was thinking was that there could be slop in the main bearings or possible bad oil pump. So far this engine I bought from CNS motors is really starting to suck. I wish I had rebuilt the thing myself.

Thanks for the responces keep them coming.

 

I have been told that loose bearings can be responsible for the behavior you're experiencing. I had the same thing with a Ford 289. Oil pressure acted normal before the oil pump shaft broke and the bearings got hurt. After that, the pressure was lower and would drop if I leaned on the gas, yet come back up when I let off.

 

Sounds normal to me.
The pistons are very bad at sealing off the cylinders from the oil cavities.
With every compression and combustion stroke you will be getting some excessive blow by that will result in higher oil pressure. Thats just a fact.
Hope its not too serous.

 

Yeah I hope it is not serious either. I have another $130 invested and the front of the engine apart for a bad upper idler pulley at the moment. The damn thing only has 30k on it and it went bad. Oh well Toyota may be great vehicles but like all vehicles they are money pits.

 

Maybe in the most technical and minute of scientific measurements, but in practicality that is NOT a "fact." On top of that, he said the oil pressure goes down when he gets on the throttle which is when cylinder pressures are highest. That's the opposite of what you describe. Besides, the crankcase ventilation system vents what pressure actually does make it into the crankcase.

Blow-by doesn't affect oil pressure unless you get a bunch of fuel in the oil and thin it out. If the engine isn't running seriously rich, then that's not the case. Being a low-mileage rebuilt engine and ASSuming the rings seated correctly, leak down should be well under 10%.

If the crankcase actually did get pressurized enough to see it on the oil pressure gage, oil would be blowing out of every seal on the lower engine.

 

Im sorry but blow by does directly effect oil pressure.
With regards to the oil pressure going down when the throttle is advanced, valves are more efficient at higher speeds.

Lets make this simple...how do you think your engine oil gets dirty with carbon if there is no significant blow by??

 

That condescending tone at the end is a nice touch. I don't need simplification. What I need is for you to clarify your definition of "significant blowby." It's not even clear if you're talking about oil dilution or thickening. A new engine does not have "significant" blowby. In addition and I repeat, the behavior outlined in the original post is the opposite of how you describe blowby to affect oil pressure.

 

Now kids play nice. Don't make me pull over. LOL

My intent of posting this was just to see if the numerous Toyota owners/ vehicle guru's on this forum had ever experienced this before, and if they knew a possible cause. So far I haven't had any significant problems related to this. I am just one of those people that are constantly looking for indicators to a problem so I can fix it before it brakes.

 

Yeah like blowing a head gasket? (ask me how I know). Those of us with the lamo 3.slow and no aftermarket gauge don't have the luxury of seeing what you are seeing. But I doubt it is predictive of anything as severe as a blown head gasket. However, you never know with a 3 slow....!

 

I have the same thing happening on my turbocharged 22re. Not sure what it is. I've only got 50,000 miles on the engine. I've done a leakdown test, and a compression test, all are fine. No oil consumption, no "excessive blowby". Everything runs fine. I have a fairly new high pressure oil pump on there (installed about 10,000 miles ago), wonder if that has anything to do with it. I was worried at first but its been doing this for as long as I can remember with no problems so I've stopped worrying about it.

 

I have pretty much stopped worrying about it as well. I bigger fish to fry, such as putting a new knock sensor in and figuring out what else is going on with my engine. It's always the little things that get ya.