The Triumph Dolomite Club - Discussion Forum

Leaving the rad cap off the header alone wouldn't make any difference. I always leave the cap off any car (not just Dolomites) that I have drained and refilled until the engine has run long enough for the stat to open and the coolant level to stabilise, then I top it up and fit the cap. I'm also still inclined to remove the original filler plug from the stat housing when filling to improve self bleeding of the system. But that doesn't get round the pump housing airlock possibility either. Only a running pump with enough power to push the trapped air into the block and thence upwards through the stat housing and into the header via the thin pipe will do that. On my controlled EWP system the pump doesn't run at all on startup and only gives 10-30 second pulses during warmup, so it's doubtful if the pump would run enough until the motor is pretty hot. Which sounds a bit risky to me!

Maybe i'm being overcautious, I call it outwitting Murphy's Law! 50 years in this business has given me a sensitivity to airlocks on refilling, I can tell from the way the water level in the header behaves on warmup, when to suspect one. But I am very aware that not everyone has my wealth of experience and could make an expensive mistake through no real fault of their own. So when I design or mod something, I try to make it as foolproof (or even squaddie proof, a much higher standard) as possible! Someone MUST agree with me, or the modified bypass pipe wouldn't exist!

Steve

can you explain to me how a header tank with a screw top cap,releases water went they over heat

They caps are built to withstand a certain pressure (something like 18 or 20psi I think),
if the overheating causes the pressure to reach this then the cap will allow the coolant to spew out.
After sorting the cause, you then need a new cap.


Ian.