# Oil Pressure Sending Unit



## GT500blue (Aug 27, 2007)

Hi, I have an oil leak that only happens under load. It is on the fire wall side of the engine and must be high up on the block since it does smoke, so I'm assuming it's running down the block or hitting the exhaust manifold.

I'm thinking it could be the oil pressure sending unit. I'm not sure where it is located on the engine. 1986 300zx. I think it must be either this or some other seal or gasket since the car was fine with no leaks or smoke when i put it into storage for about 2 years. THen after getting it out of storage, this leak appears.

Again, it can idle all day with no leak or smoke. But once I put a load on the engine (drive it a short distance or hold the throttle open at idle for a longer period of time), the smoke starts to blow up from the back of the motor.

Ideas? Does anyone know where the pressure sending unit is located on this engine?

Thanks so much!


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## Zen31ZR (Mar 24, 2004)

Could just be a valve cover gasket leak. IIRC the oil pressure sending unit is on the side of the block..... Time to invest in a factory manual, you'll find out what could be leaking pretty quickly. Is the car a turbo model? There are additional oil lines that can leak with those .


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## GT500blue (Aug 27, 2007)

Zen31ZR said:


> Could just be a valve cover gasket leak. IIRC the oil pressure sending unit is on the side of the block..... Time to invest in a factory manual, you'll find out what could be leaking pretty quickly. Is the car a turbo model? There are additional oil lines that can leak with those .


Thanks for the help! The first thing I changed were both valve cover gaskets when this leak showed up. It was my first guess. Even though the RHS is such a PITA to change 

It is not turbo, and the only other gasket I suspect it might be is the actual head gasket. However, there is no coolant in the oil and no oil in the coolant. My concern about the pressure sending unit is from what I can tell, the unit is down by the oil filter housing, so I don't know how the oil cold get up to the hot part of the engine enough to smoke...?

I am selling the car, so investing in the shop manuals is something I'm trying to avoid. I rebuilt the engine several years back and basically parked it (ran it for about 600 miles) and then moved and did not have the room, so I stored it. Now I have it out of storage and this leak appears. So I was hoping it was a rubber gasket or something other than the head. 

I will climb under the car this weekend and spray it down with brake cleaner and see if I can see if it's the sending unit. Thanks again!


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## Zen31ZR (Mar 24, 2004)

Yeah oil does not have a tendency to drip upwards, fortunately. I think you are just looking at one of the VCG's. Probably dripping on the exhaust crossover pipe. Pressure build up in the valve covers caused by blowby, especially on an engine not completely broken in like yours might be, (600 miles is close, but 1000 is better) can force oil out of a weaker area of the gasket. I'd remove the offending valve cover and check its edge on a smooth piece of wood or with a level if you have one, you may find it slightly warped or bent just enough to let oil pass.


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## GT500blue (Aug 27, 2007)

Zen31ZR said:


> Yeah oil does not have a tendency to drip upwards, fortunately. I think you are just looking at one of the VCG's. Probably dripping on the exhaust crossover pipe. Pressure build up in the valve covers caused by blowby, especially on an engine not completely broken in like yours might be, (600 miles is close, but 1000 is better) can force oil out of a weaker area of the gasket. I'd remove the offending valve cover and check its edge on a smooth piece of wood or with a level if you have one, you may find it slightly warped or bent just enough to let oil pass.


Thanks for the help! I don't think it's the VCG as I just changed it and I have put cloth tape around the back of it to see if it was leaking. The tape stays white and dry but the smoke is still there.

I'm trying to sell the car and have a lot of interest. However, I don't want to sell it without knowing what is leaking. I'll keep plugging. 

Are there any other components I'm not thinking about on the passenger side of the block that could be up high enough to have oil smoke when it leaks? I'm stumped. I am thinking I need to put some die in the oil and clean the block and see if I can spot it.


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## Zen31ZR (Mar 24, 2004)

Sometimes a new VCG can leak, just simply because most aftermarket isn't as good as the OEM Nissan gaskets. My '85 with 160,000+ on it didn't leak a drop out of the VCG's. If you used OEM, good for you. 
I'm trying to think of what is back there on that side and I'm mostly at a loss. I know the EGR is back there.. Another possibility is that its not really an oil leak at all. I know some coolant hoses make their appearance back there, coming from the throttle body. That's mostly on the driver side, but a small amount of coolant could make its way, or be sprayed from a pinhole leak, across the engine maybe. Surely you probably notice some loss of coolant by now, though. Just an idea, keep your options open.


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