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Radiator boiling over. Ok, so what am I missing?

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(Bedford MW)Always had trouble with the old radiator boiling over and I put this down to the umpteen years of Radweld I assumed had been put in and was blocking the core. Took the plunge recently and had a new core fitted, but it still is boiling over. If anything even sooner than the old one!:embarrassed: New fan belt fitted, correct tension as per the book. Water pump appears to pump the stuff around, so any ideas as to what else could be the cause?:confused:

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Is it boiling over, or is it just spirting some out of the pressure relief valve when running? Ours kept doing this, we were over filling it as they shouldn't be filled to the top of the filler neck.

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Hi this is general info for most vehicles

First thing to double check would be the new core, as you say it seems worse, make sure you have at least the capacity of the original (not necessarily the old) and it is generally a good idea to add a core with an extra row of tubes on older vehicles, next the thermostat generally they are of two types, single and double stage, the single does two things it opens at operating temp but also restricts the flow due to the size of the opening so if you have one fail don't just take it out but do remove the wax workings and disc arms etc and just fit the plate with the hole in it, although they are easy to test in a saucepan on the stove, the two stage has to be replaced because as it opens it closes a bypass hole.


Also be very careful the system is full, bleeding by pulling top hoses etc,.


Make sure it is running well apart from the overheating, all cylinders firing, exhaust smoke, excess exhaust back pressure, no detonation or knocking.


look for obvious signs of head gasket, head or block damage, water in the oil, oil in the water, water in the crankcase, (cap or breather), A digital pyrometer is excellent at measuring water temps throughout the system and will give a good indication of flow. If all looks good and water is not being obviously blown out by combustion gas pressurising the system I would move on to the water pump, quite rare but I have seen corroded impeller's and ones that have cracked or just dropped off, quick test would be to watch level in rad under cap as you rev it, (if you can) it should initially drop.


If all looks good at this stage you have covered the basics and it is still overheating you need to know exactly what is going on, there it a clear plastic piece of test equipment that connects into the top hose it has a flow gauge a temp gauge and a pressure gauge built in, also there is a chemical test piece of kit that pushes into the filler neck, and allow any gas or steam to pass through the liquid if there is any combustion gas present it turns the liquid from blue to yellow (in the last one I used).


Heavy calcium and rust build up on cylinder liners and inside blocks and heads can cause problems, I've never tried chemically cleaning and would be a little hesitant but I guess it is worth a try if all else fails before stripping engine.


Sorry I don't have more model specific info but I hop this helps.

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