Hi,

I bought my 1983 coupe last year and was looking forward to a summer of playing. Unfortunately it suffers from a serious overheating problem.
Within a minute of starting it up the engine temperature gauge is in the red. Initially i thought it was the rad. New multi core allegro rad later and still the same problem.
(New Rad was 1/4 of an inch longer than the old one so i had to make some new bonnet brackets.

Next i tried the water pump. Had a new 1275gt high performance water pump and ported it out to ensure best flow. Still the same trouble. Its alright when it gets going on the road
at around 40mph but the second you put your foot down you count to 20 and the temperature gauge is in the red again. Obviously there is a large restriction from the long pipes but
surely the allegro rad is more than big enough for the job. I know that the flow through the heater is not the problem as i have disconnected it. I'm beginning to think that this isnt going to be a quick fix but was wondering if any one else has had the same trouble and how they cured it. The twin cooling fans do eventually cool it down however they draw so much current that the battery stops charging. I want to be able to use the car on 60 mile run but currently don't trust it to get me home again.

(In case you didn't gather the engine is a 1275 mini lump i dont know its state of tune but i dont think its much if anything more than standard.

Sorry for the long winded post!

Thanks

Thermostat? Try removing it for a trial.

Air trapped in the system?

Cylinder gasket issue? Do You have quickly-built up pressure in the cooling sys?

Is the water flowing round the system OK? Do all the pipes get warm or is the heat confined to the engine block and head?

What sort of fan are you using?

If it's overheating within a minute of start up it sounds more like an engine problem than a cooling system failure.

Usual suspect is an airlock in the cooling system.
The pipe runs to the front radiator can trap lots of air.
Do you have a bleed screw fitted to your radiator?

Another thing to check is whether there is a thermostat fitted and whether it is working.
If the thermostat is removed you normally fit a special sleeve to maintain correct water flow through the cylinder head.

Assuming the above are all OK then it could be just the restrictive nature of the water pipes/long run not being able to pump the water.
I noticed that my GTM did not circulate water at tick-over speeds.
Cure for that would probably be an electric waterpump.
You also say that the car heats up quickly when at high revs - this is likely to be cavitation of the waterpump impeller due to the high rotation speed.
Again the cure would be to fit an electric waterpump in place of the mechanical one.

One final think which may help is to use the heater circuit for addition colling when the cooling is marginal.

Have you checked the fueling/timing, as this can cause massive overheating of the engine.

The fact that it heats up so quickly seems to me to point to this, not the cooling system.

I've removed the thermostat and replaced it with a sleeve. Still the same trouble. Im not sure what the fans are but they're not shrouded. They are pretty heavy so they might go in the bin. For a kenlowe type fan. The rad has got a bleed screw and i've had it jacked up at a silly angle to try and prevent an air lock when filling the system. It doesn't have a header tank so won't bleed itself.

The timing and the fueling are as good as they can be. As for circulation to the rad it does get warm but it takes it a while.

I'm coming round to the fact that its an engine problem but i've got other projects on the go and don't want to strip the car down if i can avoid it. Theres posts everywhere saying these cars suffer from over heating but not a lot on how people of sorted it out. One thing i was wondering was on the cross flow rad should the hot go in at the bottom and the cold out the top. I was wondering if the thermosyphon was fighting the pump.

Thanks for the input.

Hot at the top.

You need to be able to bleed the air out from the highest point at both ends of the car. If there's no other way to bleed the engine end and the stat housing is the highest point you could loosen the hose and bleed it that way.

Have you tried flushing the system out, including the engine block?
Agreeing with the others, this does sound like more than just a cooling system fault, to overheat that quickly is very suspicious.

A further suggestion, not wanting to sound %&*@# but you ARE sure it's actually overheating? It's not just a guage fault is it

I must admit I have no problems with cooling, if anything the car runs too cool.
Only thing I did was after a good flush, fit a header tank, then made sure the air was going through the radiator with some ducting/blanking off of gaps.

I did fit a set of fans on a 2 stage thermo switch, but they have never come on, even in traffic jams.

The radiator should be plumbed thermostat to top hose (hot), pump to lower hose (Cold)

The rad is the plumbed up correctly then. Its not the gauge ive cone all that.

I'll try giving the system another flush.
Kenn555 How is your header tank plumbed up?

Have you guys left the fan on the engine pulley? Previous owner removed it apparently it was too loud.

Fan removed from Engine

Have you checked the impeller on the pump?

Someone previously mentioned cavitation if overheating at high revs, this can be prevented by using larger water pump pulley. Good luck.

I think I read somewhere that often the impeller needs pressed down the shaft a little, as the gap to the back plate is too big.

Which will unfortunatly worsen the things around idle. Ask me how I know this .

My solution was large pulley + electric water pump.