Over heating ?

[plangston]

I drove the car two miles and noticed that the temp gauge showed 105 degrees, so I stopped, the fans had not cut in, on inspection the rad was not hot. It took ages to cool down, I left it 30 mins and drove it home, reaching 115 degrees, and the engine cutting out, but restarting easily. to day I remove the thermostat, which in boiling water opens, I turn on the ignition on a cold engine and it goes to 120 degrees! Now I am well confused. where is the temp sender unit. why did the rad stay cold, HELP!

[ukdj]

Otter switch (temp switch for fans) is either in the bottom of the swirl pot or in the passenger side of the rad, if you short the two pins on the otter switch together with the ignition on, the fans should switch on.

The coolant temp sensor is located on the top of the block just behind the dizzy and due to its location can lead to it being in a pocket of air rather than coolant giving some odd readings.

I would check for an airlock, make sure the coolant level is correct in the swirl pot/expansion tank if you have one and also that the feed from swirl pot to expansion tank is not furred up.

[gruffalo]

First thing to change is the temp sensor.

Rad not hot due to short distance travelled meaning the coolant not yet hot enough to to open the thermostat which you have proved works.

Fans not operating because rad not hot.

[QBee]

I agree with both the above - I think you have an issue with the temperature sender, which is causing problems with the ECU and making it try to alter the fuelling.
It's either a faulty sender, or an airlock. I vaguely favour the latter, but not for any reason I could put money on.
There are threads on here about how to burp the system to eliminate air pockets first before you change a possibly ok sender.

[plangston]

Thanks for all the ideas, I have ordered a new temp gauge sender unit and a thermostat.I will let you all know what happens when I have fitted these.
Ruling out an air lock and a faulty sender unit, all that is left is the water pump, but I thought these normally leak first!

[ChimpOnGas]

plangston said:

Thanks for all the ideas, I have ordered a new temp gauge sender unit and a thermostat.I will let you all know what happens when I have fitted these.
Ruling out an air lock and a faulty sender unit, all that is left is the water pump, but I thought these normally leak first!

I've seen it before where the water pump pulley is turning just fine and there are no leaks, but when the water pump was removed and inspected a sheared impeller shaft was discovered.

Obviously of your fans aren't running you need to focus on solving that first and by the sound of things it will resolve the problem.

The sheared water pump impeller shaft thing is rare, but it can happen.

[plangston]

I didn't want to hear that, in the bible it says it not a hard job to get it off, but it doesn't look that easy to me. the thermostat appears to work fine in a jug of boiling water.
Thanks

[Nosh]

plangston said:

I didn't want to hear that, in the bible it says it not a hard job to get it off, but it doesn't look that easy to me. the thermostat appears to work fine in a jug of boiling water.
Thanks

Had this issue when I changed the rad on my serp 4 litre - cool rad, fans not coming on, temp gauge showing insane temps (never before witnessed by man!).

This was an airlock.

Used a method of bleeding, after trawling the forums, where I:-

1) constructed an arrangement where I stuck a funnel to a hollow coke bottle
2) screwed the funnel into the swirl pot (creating an airlock so no air / fluid would get out/in of the swirl pot) and filled the funnel/coke bottle quarter full.
3) Checked levels in the expansion tank (1/2 full - tick)
4) opened the rad bleed bolt a tadge
5) continued to fill the coke bottle/funnel until fluid came out of rad bleed bolt hole
6) tightened rad bleed bolt
7) started engine - and whilst running, turn heater onto max in the car.
8) watched a $hit load of bubbles come out of the funnel/coke bottle set up
9) maintained the level in the funnel/coke bottle of about 1/4 full as the engine got up to temp
10) killed engine and let it settle / cool down (1 pint of Guinness and a forum check was just enough)
11) removed the funnel/coke bottle (getting a little fluid spilled onto the engine!)
12) went out on a drive and allowed the engine to cool
13) checked level in the swirl pot and all good

Driving now, the engine only reaches 80ish - goes upto 90odd when standing and fans come on when they should.

My otter switch is located on the bottom of the swirl pot.

Hope this helps
Nosh

[plangston]

I have now tested the sender unit and it is faulty, the resistance should be in the 1000's and decrease as it gets hotter, my measured 100Ω when cold and doesn't change much when I pour boiling water over it. I have removed the water pump while I had it all stripped down and it is in good condition. So I guess the engine did not get hot enough to open the thermostat, and I panicked when I saw the temperature was so high.

[67Fox]

Glad to hear that this is then an easy fix, and cheap(er)

[Nosh]