Oil Pressure Idiot Light On At Idle

backpacker · Aug 1st, 2003, 03:06 PM

I just picked up my used 95' Pathfinder last week and the oil light comes on while sitting at a stop light. As soon as you accelerate, the light goes off and all is fine. I check the oil level and it is OK. It was bought from a Japanese repair shop and they had installed a used long block with about 30-50,000 miles, so it has only been driven about 200 miles on the this engine. I am thinking about changing the oil and filter tomorrow and see if that takes car of the problem. I am wondering if it just has extra trash in the engine from where they put it back to together and the filter is clogged. I am not sure the brand of filter that's on it now, but I am going to buy a Purolator for this change until I can order a few Nissan filters. If this does not solve the problem, how do you check the oil pressure sensor to determine if it is bad? Any other ideas to look at before I take it back to the repair shop?

aaronford · Aug 1st, 2003, 05:10 PM

Bad news... Best case scenario is that the oil pressure sending unit is bad. However, it sounds like they sold you a high mile engine. Let me explain. Your oil pump is driven directly off the crankshaft. Therefore, at lower speeds the output of the pump should be lower, at higher speds, higher. However, your oil pump should provide an adequate oil pressure even at idle. Decreased pressure can either be due to a faulty oil pump, not likely, or engine wear, more likely. The drop in pressure you are seeing is probably due to excessive bearing clearances. Take it back... Make them provide documentation of the mileage Go somewhere else as they are likely lying to you.

jadcock · Aug 1st, 2003, 08:21 PM

Aaron gives good advice, but I would recommend something to try first. Try replacing the oil pressure switch and see if that fixes it. Most likely, the oil pump is fine, and I would say most likely, the engine internals are okay, but if this is a real oil pressure problem (and not a faulty switch), the bearing surfaces would probably be the culprit. But sometimes, if the wrong oil pressure sender was installed, or the one that's in there is getting lazy, it can be just on the threshold of showing "low pressure" when the pressures are indeed lower, at idle. I'd try changing the sending unit first. It's probably only a few bucks (it's about $6.50 for my '95 pickup) at the auto parts store and can tell you pretty quickly if you have a real problem or it's just a problem with the switch.

Good luck,

Centurion · Aug 2nd, 2003, 04:31 AM

We have a truck at work (unmentionable make) with the same problem, seems as if the oil pressure gage acts as a speedometer--starts at zero and the faster you go the higher it gets. The engine is on its way out. You can listen for bearing noise by "floating" the throttle pedal: with a warm engine idle up and keep it at a steady fast idle for a couple of seconds and and then back off and then up slowly and listen. By fluctuating the engine speed in a fast idle you ought to be able to hear any unusual noises.

backpacker · Aug 2nd, 2003, 05:52 AM

Thanks for the advice. I guess I did not make one part of it clear and that is I just bought the 95' Pathfinder last week so I don't know a lot about the history. It seems the previous owner did not change the timing belt and it broke, so we know that does to it. He took it to a local Japanese repair place and I guess he did not want to have it fixed. The owner of the shop bought it from him and then bought a used long block from one of those import companies that buys the engines from Japan when they will no longer pass that strict inspection they go thru. He said they replace all the seals and gaskets and check the engine over before putting it back together. Any thing that is worn, they replace it. I know he has been in business for many years and seems reputable, so I hope that is not a problem. Of course there is not warranty on it, so if I can't easily fix it, I hope he will at least look at it in good faith. I think I am going to pick up te sensor and replace it since it is not expensive and go ahead and change the filter on it and see what that does. I have read in the forums that some folks are installing an oil pressure gauge which requires replacing the sensor. Any advice on what brand of guage to install and has worked well for others?

1997XETruck · Aug 2nd, 2003, 10:04 AM

I wouldn't do anything except take it back first! You don't want them to have the excuse that something you did while working on it caused the problem, and the longer you keep it before going back, the less likely it is they'll help you out...

Heath

aaronford · Aug 2nd, 2003, 03:44 PM

Good call on the immediate action. Also, do not let them mask this problem by installing a thicker weight oil. This will cause the indicated pressure to rise, but at the expense of putting less oil to the bearings. If the sensor does not do it, but they fix it later, change the oil with the manufacturers recommendation and see if the light comes back on. If it does, then they have only installed thicker oil. Good Luck

backpacker · Aug 3rd, 2003, 06:05 PM

Thanks for all the advice. Since it was the weekend and the shop was closed anyway, I decided to just put on a new oil filter to see what happened. The oil on the dipstick looked like new since it had less than 100 miles on it, but the oil in the filter was very dirty. After I replaced the filter, I drove it about 170 miles this weekend and no problem, so hopefully that it all it was. I will be watching it closely the next few weeks to see if it happens again.

1997XETruck · Aug 3rd, 2003, 08:17 PM

Wow... maybe they didn't replace the filter? Doesn't sound good long-term either way. I'd keep a really close eye on things and still take it back on Monday with the old filter in hand. If the problem shows up in three or four weeks, and you haven't gotten it documented by the shop, it would be really hard to get them to do anything.

Heath

himilefrontier · Aug 4th, 2003, 12:54 AM

It is possible that the engine bearings went bad because they were essentially started"dry" because the engine sat too long and all the oil drained off the bearing surface.That's why ANY junkyard engine needs to be prelubed-either at the distributor(if it drives the oil pump) or by removing all the plugs and spinning it over with the starter.Taking the plugs out minimizes wear because there's no compression acting against the pistons.

2000SE · Aug 10th, 2003, 10:27 AM

Looking at the oil has nothing to do with it being clean.

If you changed the filter and the problem went away. I would immediately do an oil/filter change to get that old oil(and possible additives) out.

I hate engines that might' have "super goop compression builder topend sealer viscosity improver mud gel topend silencer snake oil" installed.

Doing an oil change now with the proper weight oil(for your weather) will let you know how well the engine is running.

Aug 11th, 2003, 07:49 PM

I actually had a Valvoline oil filter come apart internally back in the early 1990's when I had my '87 Mazda RX-7. The paper filter insided blew apart and scattered pieces of the filter media all over inside my rotary engine. The paper bits clogged the oil pressure sender and it gave false readings on the oil pressure gauge and the light would come on. I changed the filter and oil and the problem cleared up. I changed the filter again just to make sure anything else still floating around got filtered out. Never had one problem with the oil pump or goo in the pickup. And as wild as this sounds, just changing the oil and filter did clear up the problem. Sounds like you had something in there, but if the light comes back on, I'd change the sensor (they're usually under $20) just to make sure. For what its worth...