Diagnosis Required

First thing to check is that it is full of coolant and air is out of the system. A stuck closed thermostat would still give heat through the heater, even if it overheated.

mrcheerful

Thanks. So, assuming that it overheated due to there being next to no coolant in the system, would it be fair to say there is probably air in the system even after putting the coolant in?

Can I check that the air is out myself? How would I go about this (if its simple)?

Ruffus

wrote

Make sure the coolant is topped up, then repeatedly and vigorously squeeze the bottom radiator hose with the engine turned off. This may expel some air. Then find a section of rubber coolant pipe which can be loosened off- something just below the water level in the coolant header tank is best. Loosen it off with the engine running and wiggle it around to check that water, not air is coming out of it. Mind your fingers!

There may just be a spigot designed for this very purpose, on my car it is just behind the water pump.

Unlikely. A 'stat jammed shut would cause overheating, but the heater would still work. Jammed open, no overheating and no or poor heater.

I'd be looking at either an airlock, or a failed waterpump. For a start.

What car is it - make, model and year?

Hang on, while I get my crystal ball out...................

Ok, here goes................

I can see the mist parting, looking carefully.........

I see an N....... Niss...........Nissan, yes I'm sure its a Nissan...............

The ball is starting to glow, must be a Sunny then...............

Now there's some numbers appearing...........

Yes, that's it, a Nissan Sunny, 1995 model.

(in other words RTFP!!) ;-)

or the water pump vane has fell off

--

Oh dear...;-)

Ok. I went to try a couple of the things suggested last night. I was looking for a flexible pipe under the radiator and found one hanging in mid air attached at the engine end but not at the radiator end. I reattached it, thinking that this would solve all my problems.

I took it for a spin for about 10 mins but the same happened. The gague for the engine heat went into the red, and at no point did I get any hot air from the internal fan. Would this mean that there is definitely air in the system? Was that the water vane? How do I know if the water pump is broken?

Thank you very much Ruffus

Is the water system full? If so then you need to get any air out. If full, no air and still no heat then there is probably a water valve jammed shut or disconnected, or the heater is blocked up. Water pumps very,very rarely fail by falling apart (I have never seen one fall apart internally) they do fail by wearing out and leaking, but they will still pump water around while there is some to pump.

It sounds as though you need to get an expert to have a look for you, in the event you can't find an expert then ask friends till one of them recommends a garage to ask.

mrcheerful

I've had three on Rover V-8s where the impeller has broken up. Common on some BMWs too, where it's made of plastic.

I have heard of them, but never seen one personally, must be lucky I guess, I have seen them where the bearing is so loose that the impeller is hitting things, but they are still fixed on and working. However I would expect that mere convection would be enough to get some water round the heater, after all old cars had no water pump at all (mind you they had no heater either , so that argument won't work)

I expect the op problem is something straightforward (to a mechanic) but not at all obvious to average person.

mrcheerful

Are you saying the hose was not attached to the engine? In that case there is no water in there!

Where did you put the water when you filled it? IIRC, they have a separate expansion tank, which only feeds water into the cooling system when it gets drawn in to it by the system cooling down, have you removed the lid on the radiator and filled it there?

Thanks to all who helped. It appears that the hose had come away from the radiator and all the coolant had landed on the ground. I filled the radiator with water and coolant after reattaching the hose and it has fixed everything. Your help is much appreciated as if I had gone to a garage I would no doubt have ended up with a new radiator, new water pump and a new thermostat.

Many many thanks Ruffus.