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DanPatrick10 · Aug 25, 2015, 12:57 PM

Looking at buying a used 83 Datsun 280ZX Turbo. Owner had the top end and turbo professionally rebuilt. He's using synthetic oil in the engine. He posted a video with a clear shot of the oil pressure gauge. When the car is idling, a square red light comes on next to the gauge indicating that there isn't enough oil in the engine. The owner said that this happens because synthetic oil doesn't tell the gauge that there is enough oil. When the engine is revved up, the light turns off.

I know that synthetic oil doesn't react to temperature changes like conventional motor oil. Is what he says true, or could there be another problem with the engine? There's no leaks coming from the engine and no smoke coming out of the exhaust.

hkstroud · Aug 25, 2015, 01:21 PM

The owner said that this happens because synthetic oil doesn't tell the gauge that there is enough oil.

I don't buy that explanation. An oil gauge tells you what the oil pressure is, not how much oil in in the engine. If his explanation was correct, he would simply put regular oil in it in order to sell the car and not have to explain the oil pressure light. Synthetic oil has a higher temperature range than regular oil.

Vehicle probably has a cooling problem. Could be stopped up radiator or faulty thermostat. Could be worn main bearings. Could be anything.

catonsville · Aug 25, 2015, 01:29 PM

Ditto: I don't buy that explanation.

DanPatrick10 · Aug 25, 2015, 02:39 PM

Here's the video of the engine running with the oil pressure warning light on. Tell me what you think. Do you think it could be the oil pressure sending unit?

smoothy · Aug 25, 2015, 03:48 PM

Originally Posted by DanPatrick10

Looking at buying a used 83 Datsun 280ZX Turbo. Owner had the top end and turbo professionally rebuilt. He's using synthetic oil in the engine. He posted a video with a clear shot of the oil pressure gauge. When the car is idling, a square red light comes on next to the gauge indicating that there isn't enough oil in the engine. The owner said that this happens because synthetic oil doesn't tell the gauge that there is enough oil. When the engine is revved up, the light turns off.

I know that synthetic oil doesn't react to temperature changes like conventional motor oil. Is what he says true, or could there be another problem with the engine? There's no leaks coming from the engine and no smoke coming out of the exhaust.

He's got an engine that is either 1) Worn out... or 2) was rebuilt with excessive clearances because whomever did it failed to properly measure first and second failed to plasti-guage the bearings upon assembly to verify proper clearances. Possibly even too light a weight oil...or any combination of the above.

Or since its an idiot light, possibly a bad sensor. I would not spend a dime on it until I had an independent mechanic put a mechanical oil pressure gauge to verify what it actually has.

If it really is low...it will only get worse with wear.

I have several vehicles that I have gone from regular to full synthetic oils on...and NONE had ANY drop in oil pressure upon switching.

DanPatrick10 · Aug 25, 2015, 05:01 PM

Yeah, I had an 85 Turbo and went from conventional to half synthetic. Never had a drop in oil pressure. You're right on about it being a bad sensor. Other people have said the same thing about it in forums or on educational videos. So it will either need a new oil pressure sending unit, or the bottom end is worn out, or it wasn't rebuilt properly.

I did plan on having a car inspection done. If and when the owner brings it in for an inspection, I will ask the mechanic to put the mechanical oil pressure gauge on to verify the engine has the proper oil pressure.

Thank you for the tip, gave you rep pts for that one :)

TxGreaseMonkey · Aug 26, 2015, 04:51 AM

Likely, there are excessive journal clearances, due to wear. The wear likely took place, prior to using synthetic oil. It won't be long until the camshaft goes, since it's the last on the oil train (i.e., the first to go when oil pressure drops) and experiences the highest pressures in the engine.

DanPatrick10 · Aug 27, 2015, 09:57 AM

Things aren't looking good here. A new problem has occurred. The owner now says that the engine will sputter when revved past 4,000 RPM.

He thinks it could be the fuel pressure regulator, crank angle sensor, air flow meter, or ignition control module. He said adjusted the contact track on the AFM (MAF) last year and it tested fine.

I have never owned a 280ZX Turbo, but I have owned a 300ZX Turbo. From what he's telling me, it sounds like the ECU or the air flow meter are going out.

I know there's not way to tell w.o testing. However, I still wanted to ask, what do you guys think of this new problem?

smoothy · Aug 27, 2015, 11:05 AM

Wiped cam can do that... as can almost all of the other things mentioned.

I'd run, not walk away from this... I think he was lying about the fresh engine... and these new problems point towards why he is trying to get rid of it.

Unless it was nearly free, and you was willing to pour a lot of money making it right into it... stay away. Wait for a car that is already sorted out.

DanPatrick10 · Aug 27, 2015, 12:24 PM

Smoothy,

I believe you're right. I think I will stop and listen to everyone's advise here. It is a 280ZX Turbo 5-speed, and probably has potential. However, it probably has more problems than it's worth and will end up being a major headache.

Right now I still have my money and I don't have a car sitting here with a problem. I will wait for a better one to come along.

Thanks for all your advise!

smoothy · Aug 27, 2015, 01:28 PM

You are welcome... and if you happen to have ANY lingering doubts what so ever... ask yourself... if these were minor, simple or cheap problems... why didn't he fix them so he would sell a car with no problems and as such get top dollar, rather than take a big loss with people having to assume the problems are serious, complicated and/or expensive to fix.