QuestionHi,
I have a very weird problem with my '97 E39, 520i. 2 days after i bought the car, i drove down to a mate's place 100miles from where i live. The car was running fine the whole way, and actually reach my destination with no problem. I then sttopped the car (After approx. 2hrs drive) and when i started it again, drove 10 mins, and the indicator was on red hot. Stopped the car, fill it with water but it keeps turning back to red whenever i drive it for 5-10 mins. I took it to a mechanic and he told me that it was the Thermostat, changed that, and the car was fine again. I drove for another 20 mins when i stopped again for refuel, and when i start the car again, after 10 mins, it was on red hot. So i took the car back to the mechanic, and he found out a crack near the radiator cap. He glued this crack as it was relatively small, remove all the pressure by unscrewing 2 caps - 1 above radiator and 1 near the thermostat. The car drove fine for 20miles, then turn red hot again. So I stopped again, called a mechanic, and he came and removed the thermostat completely, remove the pressure. The car was then fine, running without a thermostat for 80miles, temparature indicator on normal the whole way. However, when i stopped again, and then drive again, the problem will persist. Then i stopped at a petrol station, let the engine cool down for around 30mins, then remove the pressure, then refill it with water (Arnd 2-3 gallons) and it run fine for another 30miles and then turn back to red. I had another mechanic to look at it, and he said that it might be the head gasket that got blown. However, the car still starts up, and drive smoothly, only the overheating. He checked the water pump, seems fine. I have drive the car for a total of 5miles while on red hot (not constantly, but if i sum up everything). But i really want a second opinion, and would be grateful if you could help me, at least to know if its really the head gasket, or just a flow circulation not working when i stop.
Cheers
AnswerHello Girish,
It looks like you have a handful here.
I would recommend going down to basics and do a point by point
recheck of your cooling system(with thermostat re-installed).
a) bleed the system by opening/removing the bleeder screws on top of the expansion tank and also in the left upper radiator hose (if there is a bleeder screw), then add water (not coolant for it could be just a waste of money at this point in time, remember that we are just doing diagnosis),
close the screw on the left hose when water flows out in a solid stream, then do the same with the bleeder on top of the expansion tank when water flows out fully.
b) do a pressure test to about 16 psi, first time around it would go down by about 5 psi, repump it again to 16 psi and look for leaks (always consider the pump pressure if it stays put or goes down).
c) with the radiator cap (expansion tank cap actually) open, start the engine and rev it up to 1500 to 2000 rpm
(you need an assistant here), wait until there is a continuous solid stream of water coming from the side of the expansion tank near the filler neck, then top off the radiator and close the cap,
d) run the engine with heaters on for about 2 minutes, air intake open (usually I do this with the left side on heater, the other side on cold but aircon off, then I do the reverse),
e) run engine to operating temperature (half the gauge),
if it does not overheat till this point, then do a roadtest of approximately 2 to 5 miles (2 will make it overheat if it will overheat, 5 just to make sure),
f) if it still does not overheat, then congratulate yourself.
g) it it overheats, ask a mechanic to do a blocktest (this one tests the radiator/expansion tank for the presence of combustion gases, if it fails, you have a blown head gasket or a cracked block.
Between steps a) to g), I am fairly sure that you will find something wrong (assuming that you have a working waterpump
which you can test anyway while you are bleeding because water will not circulate in the expansion tank if the pump is not working).
Update me of your progress if you can.
Tino
