cooling system boiling

[grumpy2]

everything was going well with my spitfire until I had some carb trouble. I swapped the carbs for some used but known good ones and the car runs fine once again except the car seems to 'boil'.

A little more info...

the inlet manifold has a water pipe running through it, suspecting the carb problem may be manifold related (cracked?) I swapped the carbs and manifold. Naturally I lost some coolant. refilling the system was easy, bleeding a little more troublesome, it took a while to get a hot heater. The car runs fine idles well and the electric fan kicked in and out at about 3/4 temp gauge.

I noticed the rad cap rubber was perrished so I changed it for the correct pressure new one. Once again the car runs fine and drives with a lovely warm heater and temp gauge just under 1/2.

but

as soon as I switch off the engine or leave it idling for more than 30 seconds all hell breaks loose in the radiator with banging, boiling and steam everywhere.


I believe there is no air in the system, the thermostat is working fine and there are no water leaks. The expansion tank is half full and the electric fan doesn't get a chance to cut in. The engine doesn't smell or feel too hot and there are no cold pipes in the system


any other ideas please?

[suffolkpete]

I wouldn't trust the temperature gauge. Your engine is running too hot. It's ok as long as the water is circulating well, but as soon as it stops, the water ceases to circulate through the radiator and the heat in the block, which is above boiling point, boils the water.

[arceye]

I have to agree with Pete that the engine must be running too hot.

Possibly the cooling fan sensor is at fault, but if the problem started with the carb change then the issue may lie there.
Has the vacuum advance pipe been re-fitted properly as if the engine runs retarded then this could cause some overheating issues. A weak mixture / intake leak could also cause you to run hot so it may be worth looking at the colour of the plugs, I don't think it would actually overheat you but perhaps coupled to retarded ignition it could be a problem.

If it isn't the carb / vacuum advance and just a coincidence then the usual culprits of water pump, air in system, collapsed / kinked hose, thermostat and electric fan are the next things to try.

I'm also assuming that you didn't disturb the plug leads while doing this, I once somehow did the firing order in the wrong direction (blonde moment) on an A series engine and the bloody thing actually ran not to bad, but boy did it ever heat up.

[grumpy2]

I agree it seems like it running too hot except there is nothing other than the boiling to suggest it is. The temp gauge reads lower now than before, the fan sensor isn't reaching cut in temp and my experience can't sense the smell or touch of an engine running too hot. It was fine before I changed the rad cap. I'm going to put the old one back on tonight and see what happens. I may try a chemical flush like rad flush.

Thanks for the suggestions

[Luxobarge]

Are both the top and bottom main rad hoses getting hot?

If not I'd suspect lack of flow - either a blockage, faulty/jammed stat or the water pump impeller is damaged or not rotating for some reason. I would NOT suspect blocked rad with these symptoms - that usually gives overheating when running hard at speed.

Cheers

[suffolkpete]

I wonder if the water level is below the temperature gauge sensor. The fan doesn't cut in because it's in the rad I presume and what water reaches there is being cooled. Since the problem only started after you removed the manifold and refilled the system, the problem has to lie there. While I agree with Luxo's comments about a blocked rad, perhaps there is a blockage elsewhere that's preventing the system being filled properly.

[JPB]

Airlock? What car is this please?

[grumpy2]

As it says in line 1its a spitfire. 1500

Rad is full and fan switch at rad bottom

Going to use radflush this weekend.

[Luxobarge]

The symptoms do sound like a circulation problem, and a few other comments also suggest an airlock. Now, given that airlocks can - in fact will - produce circulation problems (as any competent plumber knows) then for me an airlock is looking favourite here.

By all means flush it, but given that it wasn't blcoked before you did the head/manifold work, I'd be surprised if that cured it 100% unless in so doing it also somehow clears an airlock.

Do keep us updated, I'm keen to know what the end result on this one is, and all the very best with it!

Cheers,

[arceye]

Could certainly be air in the system, but have we tried the old rad cap yet?
I think it's correct to say that if the new one is a higher pressure then it will not vent as early, and so take a higher (hotter) pressure before venting, perhaps allowing for boiling before blowing off.

It could be an earlier unnoticed problem that has been brought to light by the new rad cap, with the old cap the system could vent earlier and so not pressurise as much, though this would generally be noticed by coolant loss to some degree.

I'd bleed the system again and then try with first the old cap and then the new one, it should point you in the right direction if it doesn't cure it altogether.