Bemused Mechanics!!

[rigerama]

Hi looking for advice!!

Have a 1994 E36 318i. After about 15 miles the pressure in water system gets very high and temperature goes up. Have had radiator and water pump changed. No sign of head gasket problem as mechanic checked water system with a dye thing and says no problem there. Drives perfectly with no oil or water leaks or any sign of the two mixing. Just gets hot after driving that distance and pressure in hoses gets very high. Water seems to be circulating ok. Any suggestions would be welcome. Mechanics think it's something simple but bemused as to what it could be!!

Thank you in advance.

Rich

[Jack Dabsy]

Stupid question number one is: Do the fans kick-in?

Try this... (From COLD)... Start the engine with the Rad Cap OFF, and let it run until the point where you think it is overheating, then "Feel" the top and bottom hoses...
Let me know all your results, even what happens at the radiator!

[rigerama]

Hi thanks have done this. The top hose gets hot. The bottom hose going into thermostat housing stays cold. The coolant slowly rises up the expansion chamber. Note the thermostat has already been removed. Thoughts? Thanks. Rich

[rigerama]

Also by fans assume you mean radiator fan? If so yes it's on permanently as on the belt. If you mean fans in car then yes they do and blow out lots of heat when driving. Have had them on at times to help bring engine temp down. Thanks. Rich

[brettski]

Was this all happening prior to the water pump and radiator being changed?
Is the thermostat installed at all? There may be a large air lock that is isolating the coolant from the thermostat body (the thermostat isn't opening because it isn't getting hot enough). You could try drilling a small hole through the thermostat housing which will let air purge past the thermostat, and then it should behave normally.

[rigerama]

My friend had the car - all was working fine - the thermostat was working fine (it was a relatively new one that had been put in as the previous one was stuck in the open position - and had done about 3,000 miles since thermostat replaced with no problem) - he was stuck in traffic for a while and it was getting warm. He kept switching the car off to avoid overheat. Car was parked for three days, then he drove it again and there was a bang and a hole blown in side of radiator. Radiator was changed - still high pressure building in system after about 15 miles. Thermostat was removed - still high pressure in system after 15 miles. So, there is no thermostat in the car - and all was fine until the radiator blew. Seems to be pressure building up in the system somewhere - but just can't work it out!!!

[brettski]

Is there a air purge line that runs from the top of the radiator to the top of the expansion tank. Check that it isn't kinked.

[rigerama]

No afraid not expansion tank is on side of rad.

[rigerama]

Been looking at it today. Coolant going round fine. No blockages and no contamination. Just intense pressure build up after about ten to fifteen minutes running and then overhears. Should the cap be releasing pressure? Ideas? Thanks.

[Jack Dabsy]

TBH There seems to be intense pressure in there...
Gotta be head gasket mate... Sorry !

[brettski]

If you leave the cap off the expansion bottle, do you see any signs of bubbling, and do you see the same pressure build up? Are the upper and lower hoses showing the same sorts of pressure buildup?

[Frozen 318i]

if it not the head gasket it could be the head itself, My car did the same thing i thought it was the head gasket until i pulled the head and found a cracked water jacket.

[Frozen 318i]

also check to see if your check valve and auxiliary water pump is working it is located on the fire wall in the fuse box area

[rigerama]

If cap off pressure pushes water to top of radiator. Thanks for all your advice. I'll check the electrics as suggested. Any further ideas greatly appreciated.

[jimmythepie]

Go to a reputable mech who only does BMW, if it costs its worth it.