I have a the 3.0L in my truck, it was rebuilt by Toyota 8K miles ago under the head gasket recall. When I start it up after it sits all night and gets cold, it has plenty of good oil pressure on the gauge, after it heats up a bit the oil pressure drops almost completely out, on the gauge at least.

It doesn't knock or tick at all and I can see plenty of oil moving around in the head when I take the oil cap off, when I rev it oil will fly right out of the cap hole with the cap off. This is when it's hot and the gauge shows almost no pressure.

Is this most likely the sender, or could my oil pump be shot? I don't think an oil pump would just cut out like that, if it was bad it would just be bad all the time right? Would Toyota have used the same oil pump on the rebuild, that came off the old engine? It was rebuilt by them at 188K and now has 196K.

I have heard that the pressure senders do go bad on these things, and if they used the old one when they did the rebuild it's not hard to believe it's bad. I just hope it's not the oil pump.

Any suggestions would be great.

Thanks.

Find one of the oil galley plugs on the block and screw a pressure guage in and see what you get.

I'm unsure if there's a checkout for the sending unit and cluster guage; we have an FSM for a '93 sticky'd here that you can take a look at for them.

mine does that too, at idle, but when I step on the gas it shoots up again. watch it on the road, when you take off from a stop and rev your engine to like 2500rpm, does it go up a bit? I always figured that as the oil warms, it loses viscosity so the pressure is lower. <img src="/forums/images/graemlins/sleeping.gif" alt="" /> also when you start it from cold it idles at 1200rpm(mine does) so the pressure should register higher at 1200 rpm as opposed to 700 rpm or whatever it idles at warm.

>>>*The good sign here is the lack of any noises, and the fact that you know oil is moving on the top end.

Any lack of oil volume normally lets you know fairly quickly.

The oil pump and oiling systems on these engines are almost fail proof, the pump will push oil even when nearly completely worn out.

Low idle pressure that recovers quickly with RPM is nearly always related to more than normal main bearing clearence or the bypass, I would hazard a guess that an oil pump failure concern in this situation just doesn't happen.

What CAN happen is the bypass valve sticks open, (the usual dirt/debris/swarf, etc)this will cause lower than normal idle pressure yet quick recovery with RPM increases.

She will likely run just fine that way for the rest of her life but it makes a person nervous.

Of course you want to be sure before you hear the loud noise and see the big cloud of smoke. And then go, "OH! That's what that was!"......

Best to get a remote gauge on there and check, one of Toyota's weak links is the gauges, I have seen lots of those that just don't work real well....*EB

Thanks for the responses guys.

The engine was completely torn down and rebuilt by Toyota 8K miles ago, so I'm not sure that the main bearing clearance would be off. I have to assume everything was cleaned when it was apart, but I gues the bypass valve could be stuck open even after only 8,000 miles.

I thought about the viscosity breakdown as well, but even with normal viscosity breakdown you would still show in the normal range on the gauge, my gauge is bottomed out at warm idle,and this happens after about 5 minutes of driving, it would have to be pretty crappy oil to lose that much viscosity that quick.

It will go up some when I come off idle when starting to drive or if I rev the engine, but it will only go up to the first line on the gauge, which is the Low point of normal pressure on the gauge. It doesn't go back into normal range at all after about 5 minutes of driving, once it gets a little heat in it, it just stays at the low point while driving and then drops out completely at idle, same spot on the gauge as when you shut the engine off.

The gauge seems to work fine when the engine is cold, the pressure is in normal range, and even kind of high, when first started at the high(1,200RPM) idle when cold, but as soon as it gets any heat it drops right out.

Would the sender drop out when it got heat to it, or possible when the oil does start to thin out with heat, then the sender doesn't read right??

I'm glad to hear that the oil pump and oiling system is pretty tough, but since I can see all of that oil flying around in the head, I was sure they were working.

I will try the manual gauge in the block. Can somebody tell me where it needs to screw in. I'm new to this engine, only had it a week, and my old Jeep had way more room in the engine to work, so I'm still getting used to it.

Thanks for the help guys, it's appreciated.

Mike

I had the same issue w/my '90 3.0, and was concerned w/how low it was when at idle and at 3k rpm's, so I installed a set of after market gauges for oil press., water temp, and an A/F gauge. With the new gauges the oil pressure was right where it should be. Like others have said it is likely just the gauge, no oem gauges other than those on high dollar cars are going to be that accurate.

With the rebuild it is likely that Toyota just replaced those parts that were covered under the HG warranty, unless you specified otherwise.

Thanks for the response.

I didn't have the engine rebuilt, it was the owner before me, but I assume your right and they used the original parts, ie. oil pump.

I still don't understand how the actual gauge in the dash could be the problem, when all it does is get a signal from the sender, based on a difference in volatge and resistance within the sender. If it works fine on a cold start and then drops out with some minor heat, how can it be the gauge? The sender is what is sitting on the engine and taking a reading.

Does anybody have any experiecne with the oil pressure sender?

Thanks.

no experience per se with 3.0L - but the sender could be replaced if suspect.