Overheating solved

[ETobing]

My long outstanding overheating issue was finally solved. It was the upper radiator hose that leaking somewhere around the area where it is clamped. The leak was so tiny I could not spot it. It leaves no coolant trace either.

After having to replaced the radiator due to leak at the bottom of the expansion bottle and fan clutch about a year-and-a-half ago the car running with this frustrating overheating issue ever since. I had to replace the thermostat housing twice since the first one was non-OEM part it didn't seal correctly especially when pressure inside the system rise while driving the S or M mode.

The same situation happened with the old hose. The leak was not that obvious it still can hold pressure while driving with D mode. Ed, Craig, Jimlev and many others were right: I should have done pressure test months ago!

Now I am sure the system is perfectly sealed. Bleeding process was not hard at all. I have been using the S and M mode for the last couple of days without worries. The side effect was good too: the auto transmission shifts much smoother! I remember this advice posted in E34 forum when I joined the group few years ago: bleed...bleed and bleed some more!

Thank y'all!! :)

Rgds,
Enrico Tobing

528i E39 1997
Automatic ZF 5HP18

[jimcash]

According to the posts on these digests, and my own experience a number of years ago with a mysterious minor gradual drop in coolant level I strongly suspect that there are many cars out there with very minor leaks around hose fittings.

The leak is just enough to let vapour out when it is hot, and then allow air to be pulled back in for a short time till it cools again.

This will gradually replace coolant with air, and also means that your system never reaches full pressure so you may also be getting boiling at the hot spots inside the engine (more air into the system and also poor cooling at those points).

ANY sign of overheating, or ANY sign of lowering of coolant level should always be investigated - a full pressure test (hot and cold) is advisable. You need to look for a very gradual loss of pressure.

Cheers
Jim Cash

[Ed CT]

Enrico, you must feel like you have a new car now!! Glad you found the problem.
Ed CT
1998 528i (aka, best car I ever owned!)
5-Speed
Aspen Silver
Aubergine Leather
Zeckhausen CDV
Nokia CK-7
D-Con Cache on Fuel Pump Cover

[AussieBob]

Did the hose look damaged or perished from the inside surface or was it just a pin-hole break around the clamped area? Did you replace all the hoses?

It's amazing how fault prone these systems are, but it's part of the pressurized system I guess. Anyone know if rubber handles cold temperatures worse than hot? Australia is mostly always above 10 deg.C (50 deg.F)

Now you can go and drive the engine into the ground again, but like me you will probably look at the temp gauge all the time and pop the hood to have a look. I've never experienced the overheat again but I know it will return again one year if I lower my guard.

[ldog]

I've fought the issue for some time. It's my opinion that there is a very small crack in the head gasket---so small that it's not detectable by block testing kits. It takes about 8-12 months. Coolant is burned off, and some air develops. I elevate the nose, open the bleed screws while car is running, turn the heater thermostats to max. Then remove the bleed screw at the thermostat and add coolant through that bleed opening until full. All will be well for another 8-12 months.

[Blaumax]

Why does BMW use a high pressure system? Is this for better pollution control through higher engine operating temperatures? Better gas mileage? If so, is the trade off worth it? Seems like the my brother's Infiniti G35 does not have a high pressure system.

[jimcash]

Well there may be many reasons - but the items you mention are certainly major factors in the latest cars.
They want the engine to operate at higher temperatures for efficiency and emissions - and that means a higher pressure system.

Now BMW uses a "closed loop" system - which means that there is no connection with an external "overflow / reserve" tank where you fill the coolant - and the overflow tank is not at pressure.

Instead the BMW system has an "expansion / reserve" tank that contains a specific amount of air - trapped at a point above the coolant level and held at pressure with the system. The pressure release cap is on this tank, as opposed to on the top of the rad on the other system.

This is not new - this was on my 82 BMW although the expansion tank was more remote. Basically this method of operation means that the coolant is never exposed to the outside atmosphere, and therefore is less likely to pull in air if the reservoir tank goes empty.

The higher pressures also mean that there is less chance of localised boiling at any "hot spots" inside the engine - therefore no air introduced to the system by boiling action.

I am sure that a BMW engine guy would be able to talk to this for days - but I don't have that level of detail or time :-)

Cheers
Jim Cash