Overheating - caught it early

philgarner

Member
Messages
226
Went out for the final drive of the year, started down the motorway and noticed the temperature was higher than it should be. Luckily we live near a services where you can sneak off onto country roads. I was already suspicious as there seemed to be no heating even after driving 3 miles or so. The temp light came on and I shut the car off and let it cool down a bit. It had plenty of coolant in. After starting again after 5 mins, the heat was back and the temp mostly under control, so limped 10 minutes home.

The last time I drove it was a couple of weeks ago, 25 miles all motorway, and I noticed the temp gauge was sitting higher than normal though nothing that looked particularly scary. What's our most likely suspect here, thermostat? Water pump?
 

Gecara8183

Junior Member
Messages
74
Went out for the final drive of the year, started down the motorway and noticed the temperature was higher than it should be. Luckily we live near a services where you can sneak off onto country roads. I was already suspicious as there seemed to be no heating even after driving 3 miles or so. The temp light came on and I shut the car off and let it cool down a bit. It had plenty of coolant in. After starting again after 5 mins, the heat was back and the temp mostly under control, so limped 10 minutes home.

The last time I drove it was a couple of weeks ago, 25 miles all motorway, and I noticed the temp gauge was sitting higher than normal though nothing that looked particularly scary. What's our most likely suspect here, thermostat? Water pump?
Hi on 3200 there is a relay that turn the second fan on just under the rad. It burns out so the second fan will not work
 

philgarner

Member
Messages
226
Fans were working as I put it back in the garage. We were then late for our national trust appointment (! lockdown dad life) so didn't check hoses etc.

Water pump working intermittently is my favourite so far. Access looks challenging - always good to have a winter project I suppose?
 

midlifecrisis

Member
Messages
16,102
Check coolant tank to see if you have coolant left. It you do, then suspect fan not working, airlock or blockage. If you have no coolant, water pump, tank or hose leak.
 

Oneball

Member
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11,075
Didn’t realise it was a 4200. I’d have thought if you’d lost the water pump you’d loose the oil pump too. So I’d go with Conaero’s suggestion.
 

philgarner

Member
Messages
226
Yeah just seen it is combined oil and water pump, that makes less sense then since it obviously had oil pressure. Good news as they are £1100+vat!

It has coolant in at a good level, I changed it maybe 18 months ago. I'm thinking thermostat (bound to be original so 15 years old) and flush the system and go from there.
 
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FIFTY

Member
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3,100
Are you certain the fan was working at 100%?

If the fan resistor has failed then the radiator fan will be stuck on the low setting

This however will not cause overheating if cold air is getting to the radiator while driving down the motorway. It would be more likely to overheat while stationary
 

RJ237

Member
Messages
107
I replaced my fan resistor recently. Prior to that there was only high speed, now I have both. The resistor reduces fan voltage, so it doesn't make sense that there would be low speed only if it failed.

Thermostat stuck closed would definitely result in overheat and no heater output.
 

zagatoes30

Member
Messages
20,759
Overheating on motorway would suggest water not circulating through the radiator rather than a fan issue. So probably thermostat stuck, water pump or airlock. Alfas have a habit of the water pump impeller breaking up or become disconnected from the shaft, pump turns but no water being moved.
 

FIFTY

Member
Messages
3,100
I replaced my fan resistor recently. Prior to that there was only high speed, now I have both. The resistor reduces fan voltage, so it doesn't make sense that there would be low speed only if it failed.

Thermostat stuck closed would definitely result in overheat and no heater output.

Fair enough... The resistor on my car had failed upon purchase and the fan was stuck on low. I diverted it so it ran at full speed until I got a new resistor installed

What about "venting the heads"? That might release any potential air locks.