Oil Light

[Tripyrenees]

Hi
My oil light is coming on after a few minutes on my '79 GTL. It started off coming on after good 20 mins but now is coming on sooner, after idling for a few minutes.

Plenty of oil in there so could it be the oil pressure sensor or possibly the oil pump itself.

Any way of checking either before I go diving in.

Thanks
Ian

 

[malcolm]

The oil light is shared with the temperature sensor (unless you have modified the car). Could it be overheating?

 

[Tripyrenees]

I just put a brand new radiator, thermostat and fan switch in. Could this be connected, I wonder.

 

[malcolm]

Is the system properly bled? Trick to doing that is (when cold) remove the radiator cap and fill completely. Then unclip the expansion bottle and place it on top of the front wing. Open the heater bleed valve and squeeze the top hose so air or water comes out of the bleed. Close the bleed and release the top hose to suck water from the expansion bottle, and repeat until you have water coming out of the bleed. Then quickly and repeatedly squeeze the top hose to push air out, and top up the radiator cap. Keep doing that until the top hose feels like it is full of water not air. Then put everything back in place and run the engine until the fan comes on. Let everything cool overnight and top up the expansion bottle and radiator if necessary.

 

[Tripyrenees]

I had done this but I have just gone through it again, with lots of liquid bleeding out, the radiator overflowing when lifting the expansion tank.

I started the engine and left to run, oil/temp light comes on after 10 mins. Fan comes on after about 20mins, stays on for a good 5 to 10 mins and then goes off.

I disconnect the temp sensor wire and the oil/temp light goes out.

So could it be the temp sensor - as the fan temp switch seems to operate on and then off.

 

[malcolm]

If the fan is coming on and going off by itself and the water isn't boiling then the cooling system is working OK. It's worth checking the wire to the temp sensor on the head isn't shorting on the exhaust manifold. Other than that it does sound like it might be a faulty sensor. Retarded ignition can make that side of the head hot, but I can't see that causing the trouble at idle.

 

[jjad]

We had exactly the same issue with the oil/temp light coming on even though I thought I'd bled it correctly and the temp sensor was new.

Turned out to be retarded ignition timing due to worn points as Malcolm suggested! Got timing corrected and light stopped coming on.

Let us know if that solves it for you.

 

[Tripyrenees]

Hmmm, I have also messed around with the timing (assuming I had done it right). I will look at this again before buying another sensor.

 

[Tripyrenees]

Thought I had it - the light came on about 30 mins into driving. But when stopped it cooled down and was the same coming home.

So it is a temp issue with the head I think - I set the timing statically as per Angles instructions. Anything else I should be thinking about (other than buying a new temp sensor)

 

[petak]

I would test temp sensor if it is possible.

Somewhere in R4 books might/should be info what resistance sensor is sending on which temp.

Use multimeter and measure resistance.

To be honest did not ever look for that info in books/manuals so do not know does it write somewhere.
But it worth to try. It is definitely cheaper than new sensor (if you have multimeter)

 

[angel]

There is no negative temperature coefficent resistance in this sensor, it's a simple on-off bi-metallic contact.

It should close the circuit at 112 deg. C. There is a simple test to check if it's closing earlier: submerge it in boiling water (100 deg.C), and check it with a multimeter. It should still be open (no continuity)

 

[petak]

Did not know that angel...but even easier to test sensor.

Good to know!

 

[mr-reno-139]

At 112 degree if you ignore it when it comes on engine damage and or head gasket failure is guaranteed

 

[angel]

Indeed!