Oil pressure and temperature

[kuyz]

Hi everyone,

 

I need some advice related to engine oil temp and pressure.

 

First off my car is a '81 280zx, automatic, stock everything as far as I know, so everything is old, except I recently rebuilt the engine. (less than 4,000ks). (all I did was replace rings bearings gaskets and repaired head, and new water pump since the head had corroded and was leaking coolant into oil, didn't replace the thermostat as it seemed to work at the time)

Recently got radiator flushed but they had to cut like 3 tubes from the radiator and there is a bit of damage at the bottom of the radiator so I'd say it's about 80-90% good.

 

Anyway my engine oil seemed to get rather hot (middle of the gauge-90C?). When I pulled up to the lights in drive, at idle speed it couldn't make enough oil pressure and the red light would come on. It seemed ok in neutral as the revs were few hundred rpm higher, just enough to get it out of the danger zone. So I assumed the radiator was unable to cool the engine properly since the water temp was also up in the middle of its gauge (~90C) and trying to start the engine at this temperature was near impossible as the starter motor seemed to be useless next to such a hot block.

 

So I got the radiator flushed - massive difference engine runs at about 70C. But the oil still gets to 80C and pulling up to the lights yesterday the low oil pressure light still came on!

 

So whats happening, is the oil to hot and thus to thin to be pumped effectively?

-using 20/50W non-synthetic oil

 

This being said the ambient air temp was 37C in the shade and I put my thermometer in the sun it went off the scale (more than 55C). The car was in the sun the whole time I was driving.

 

I presume this isn't normal for a old z car?

Any suggestions much appreciated  as I would really like to go the "slightly south cruise" this weekend. It has good oil pressure while driving so I'm wondering would it be ok to drive it a few hundred k's at highway speeds?

 

Thanks,

Kuy

 

[.]

My 280zx under normal conditions runs at normal operating temperature with good oil pressure. I did have it on the track a few years ago and after some hard work the coolant temp had risen to about 70% from its normal 55% mark. While on the track, while maintaining some revs, the oil pressure still seemed ok. As I pulled of the track with the engine idling the oil pressure dropped to nothing. I believe this to be thinning of the oil due to heat.

 

With that experience in mind I included a larger sump and oil cooler when I built my 240z. It really did the trick. My 240z temperature does not vary more than about 5% no matter how hard I drive it.....(I won't mention the time I tried running it without a fan though)

 

Be careful. Run an L series engine at the hotter end of the scale once and you will probably get away with it but start doing it regularly and it will eventually bite you. Repeated heat will effect the metalurgy of the head....So I am told (I am not an expert)

[kuyz]

Thanks man,

 

Very helpful to hear someone else's experience. I feel a lot better knowing that you have also had this happen haha.

 

Ill keep a close eye on the gauges and if it persists I might be bugging you for more info on your oil cooler 

 

Kuy

[.]

The oil cooler is just a run of the mill cooler. But you need to make sure all the fittings have the largest possible diameter to ensure you don't restrict oil flow. You will need a sandwich plate to fit between your block and oil filter to divert the oil to the cooler. Make sure to use good quality braided hoses to and from the cooler (you don't want them springing a leak). That is about all there is to it....unless anyone else has comments.

[Lynton]

You don't think the oil pressure switch is dodgee, after all they are pretty old and they get caked with gludgy black oil and fowl up 30years of driving, maybe the pressure switch is not sensitive to what is really happening giving faulty reading other then when engine is in full motoring.

Lynton

[luvemfast]

While we're on it.

Where is the oil temp pickup?

Since I transplanted the engine, I have had no oil temp.

 

[.]

The 280zx had it in the sump. But if you don't have that sump you will need to sort out another sensor. Some use a Tee peice before the oil pressure sensor.

[luvemfast]

The 280zx had it in the sump.

Yeah, thats what I thought.

Next to the sump plug.

I did't have any extra wires left over down there, so thought it must be somewhere else.