i have recently purchased a mitsubishi rvr and it was about 6 weeks ago when i looked under the bonnet for fuses, that i saw the rad cap was perished so i went and bought a new rad cap and then that opened up a whole can of worms it seems that the new cap is causing it to overheat, and it now seems i have a big problem, as soon as i turn the engine over the water is shooting up to the radiator cap, the whole system is pressurising as soon as the engine is turning over.

is the headgasket gone or could it be a water pump problem any advice would be great.

another problem ive come across is the engine is not turning over from the key but if i bypass the key and use a high guage wire to the starter and then to the battery it will turn over and pressure up the pipes, i have carried out a pressure test and it held pressure ok. does anyone know what relays control the starter

thanks

1 . Juss cause the cap fits , it may not be correct. certain cooling systems have different pressures , so the cap needs to meet the system pressure. If not it will cause air in the system and also coolant to easily back flow into the resivior thus evacuating teh system of most its coolant and causing it to overheat.

2. the overheating will deteriorate the head gasket and the cylinder head. Bur first the head gasket. To which compressed air in the cylinders will find its way into the coolant passage and over pressurize the coolant system and in some cases destroy the radiator.

If the overheat problems started right after you installed a new cap then most likely there's a problem with that cap. There are 2 different height caps that are common on most modern radiators. The shorter one will screw onto the longer style but it does not seal, thus what you see coolant going to the overflow.

It's the wrong part for the car. If you still have your old cap, compare heights.

no starter with the key, does it have an aftermarket alarm with starter kill? Might be the electrical portion of the ignition. Or it had an alarm at one point and the patch job from removing it is causing problems.

what year of vehicle? You give all info but the year, might help when looking for wiring diagrams

hi thanks its a 1994 on an L reg the caps was identical because i ordered one and was supplied wrong so i took my old one and got a new one and the both had 0.9 on the cap so i assume thats the pressure