Overheating Issue

[Z82]

Hi, I have been lurking a while and signed up today.
I recently bought a B2 90 quattro with a chipped 3B under the bonnet.

The car was rarely used by the previous owner but they did give it a full service approximately 18 months ago, this included new timing belt, water pump & thermostat.

I had to drive it 400 miles home (which is by far the most its done in a long time) and there were no issues other than my engine temperature gauge not working which I knew about.
The next day I took it out and got about 2 miles when I could smell coolant as I was only 2 mins from my house I continued home, just as I got on my street steam started belting out of the bonnet and as I pulled in my drive the over heat light came on.
I noticed the fan wasn't running, I shorted the rad switch and it ran fine so assumed that was the issue, I replaced this and filled her back up to do a coolant flush, ran the car for 10 mins, fan did not come on and top radiator hose was getting very hot but radiator was cold. I did however notice a squealing noise that I hadn't noticed before which sound like a belt or similar.

I have since checked the thermostat and it did look brand new and it opened in a pan of boiling water and closed when it cooled.
I have removed all hoses from radiator and all seem OK and are clear of blockages
I looked at the water pump and it too looks brand new but didn't want to touch it being timing belt driven?
Radiator looks decent condition and water flows through it OK.

I'm not particularly knowledgeable with cars so possibly at my limit here.

Any advice would be greatly appreciated before I have to go down the mechanic route.

[Mikes2]

Hi and welcome. Was it an overheat warning or just a low coolant warning ? It could be you have an air lock. Your rad sensor is at the bottom so the hot coolant has to be there for the radiator fan sensor to start. That really only happens once the thermostat has opened. To clear airlocks, it's best to remove the screws holding the reservoir and lift it higher.

[Colesy]

I had a partially blocked radiator recently on an S2 identical symptoms. To diagnose I used a laser temperature sensor and tested the temp of the rad in the lower corner where the temp sensor is. Mine was 40C cooler on that side to the other. The rads can be unblocked reverse bleeding or with some decent rad cleaner. I had a spare which I swapped on though which fixed it.

[Z82]

Hi and welcome. Was it an overheat warning or just a low coolant warning ? It could be you have an air lock. Your rad sensor is at the bottom so the hot coolant has to be there for the radiator fan sensor to start. That really only happens once the thermostat has opened. To clear airlocks, it's best to remove the screws holding the reservoir and lift it higher.

Thanks for welcome.
You know I didnt even think it would even have a low coolant sensor TBH, I was in that much of a panic to stop the car I just assumed it was an over temp light. I'll need to check this out.

I had a partially blocked radiator recently on an S2 identical symptoms. To diagnose I used a laser temperature sensor and tested the temp of the rad in the lower corner where the temp sensor is. Mine was 40C cooler on that side to the other. The rads can be unblocked reverse bleeding or with some decent rad cleaner. I had a spare which I swapped on though which fixed it.

The radiator is flowing freely through both holes at the base (pipe & switch), could this still be a block or airlock? I've had it all disconnected for a couple days now.

[Colesy]

Bleed it properly like Mike suggested first if I was you. Raise the tank, squeeze the hoses and bleed from the top of the rad and the hose to the heater matrix. When you're happy it is fully bled see what the temp of the rad is like. Mine seemed to flow through both holes freely but with the engine running one route was obviously slightly more restricted and wasn't getting any flow.

[John.]

After bleeding, run the engine with the expansion tank cap off until the 'stat opens.....then refit the cap.

[Z82]

Thanks for input guys, its been chucking it down here since i did this post so not had a chance to do anything yet but will keep you posted.

[Z82]

All good guys, thanks for help.
Seems the initial issue was the rad switch and i must of cause an air lock when topping it back up so all fixed now but now my battery charging seems to have developed an issue so I must of done something when stripping the cooling down so thats todays mission