Im on the way to finishing installing a BOB in my Mk3 Capri and amongst other im having some overheating issues at idle. Engine is freshly rebuilt and running with a VEMS programmable ECU. Radiator is a Griffin 22x19x2", also installed an electric fan with a homemade shroud. No expansion tank, because the radiator is the highest point of the system.
Im thinking this should be enough to keep it under control, but appears not the case. I have the original thermostat, that i checked in boiling water, and it works.
So far i have let it go up to 102C, by that time the lower hose just starts to get warm. The fan kicks in at 90C.
One possibility would be to empty the thermostat, or drill some holes in it, but im not very keen on doing that. For one its a expensive piece to ruin, and the other is that for what iīve read, itīs a trick piece of valveing. So just making and installing a empty T piece is also maybe not a good idea.
the thermostat doesnt open until 90 degrees, so its quite possible to have 100 degrees on the gauge and the stat only just opening, as you gauge is responding to the temp it sees in the head and the thermostat the water temp at the bottom of the engine
At first i tried without a thermostat, welded up a T piece and also put in a little dividing wall to direct the flow more from the radiator to the pump. And ofcorse i managed to install it the wrong way without noticing. So still had what i thought was overheating. Yesterday, after a whole week of 0 motivation and not doing anything, i finally got round to borrowing a strobe light and a infrared thermometer. And the results: my timing was 17 deg late and my temp sensor lies about +12 degC. So after correcting the timing and putting the T piece in correctly, the heating problem seems to be solved. The engine starts better, idles better and overall runs better. I might even go ahead and try put the thermostat back in at some point.
@racing escort I dont know how much you have worked on cosworth BOB engines, the thing is that the thermostat is inside a separate T piece, not in the engine block. And as far as i know there is only one kind of thermostat avalable and it costs 200+ eur, IF you can find it.
Than again i have not worked on many different engines, there might be a cheaper alternative from a different model car/engine, with a choice on opening temps. I have heard that for example a thermostat for some model of LADA could possibly fit.
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