Overheating

[Kevin H]

Claude,

A freshly rebuilt engine will often run hotter initially due to tighter tolerances, but I don't know how much hotter.

When you say the engine is boiling, is it expelling hot water from the expansion tank overflow - what are the symptoms?

In my experience, when an engine overheats that quickly it has always been a faulty thermostat, (that's not to say it couldn't be something else though!)

Are you sure the thermostat is opening as much as it should? You could try running it without the thermostat and see what happens, or of course replace it. They're not expensive.

If you run it without a thermostat it will take longer to warm up, but it will still overheat if there is another problem.

Another thing to check, is the pressure rating on the radiator and expansion
tank caps. The water system does need to be pressurised. The cap on my radiator is 15psi /100kpa and on the expansion tank it's 13psi/90kpa.

[Kevin H]

Claude,

Has the engine ever run without overheating (since it was rebuilt)?

Just wondering if you have an engine that worked fine and something has gone wrong, or whether the engine is a completely unknown unit.

and do you know what casting number is on the 383 heads?

[Geoff Kingston]

Though it has not happened to me (yet) my mechanic pal Gareth has come across on a couple of occasions water pumps where the impeller has separated from the shaft and is not therefore actually circulating the water.
None of these failures were on a Bristol or Chrysler engine but it might be worth checking.
Also as you have the 400 block with 383 heads are the Head Gaskets the same, could a waterway be blocked by the gasket?
It does seem a very short distance to get that hot, I recently had a Cadillac doing that when the water circulating wasn't actually that hot, the boiling effect especially in the expansion tank with water being forced out of the overflow was due to the system over pressurising, I my case the culprit was the head gasket failing but other owners warned about porosity in the block which should not affect the Chrysler engine but also cracks in the block and head which could and can give similar effects.
I also remember a freshly rebuilt 411 at the event at Filton a few years ago which was doing the same thing, the owner was going to have it looked at by Bristol cars so it might be worth asking Brian how they cured it.

[Peter.Kent]

I remember watching a mechanic commissioning a new rebuild. He left it on idle with rad cap off and in due course there were various undersea eruptions and he stood by with a big can of water topping up till it all calmed down. P (from the French Alps!)

[PEU186F]

It would be useful to know roughly what the temperature is at the bottom of the radiator when the top is at, say, 120 C.