How to Check if Water Pump is Functioning or Not

[Learning]

Hi,

My '91 318i is overheating. In the morning, when the temperature is still cool, it takes about 13 minutes before the gauge slowly reaches the red zone, however, once the gauge is right in the middle, it takes about 3 to 4 minutes only to reach the red zone.

The radiator and the fan clutch are working great. The upper coolant hose right next to the coolant cap is very hot to the touch when the engine is very hot and the lower coolant hose on the passenger side is warm only to the touch. Could this be a thermostat malfunctioning? OR
could this overheating caused by water pump malfunctioning and if it's the water pump, how do I check the water pump if it is working fine or not?

[bmwm42]

replace them both and bleed it right

[Dj Buttchug]

waterpumps dont usually fail with m42. its either thermostat or the cooling system has been bled wrong

[AndrewBird]

Cold lower hose points towards a thermostat not opening.

A waterpump doesn't really go bad other then the bushings going bad. Then the shaft will have play in it and leak. Also will squeak and make noise.

[Learning]

About 5 days ago, I took my car to a mechanic who told me to replace the water pump and the thermostat which I did. The car wasn't overheating anymore, the gauge needle was now in between the middle and 3/4 marks. However, suddenly yesterday the car would over heat again. The gauge needle bounces back and forth between the 3/4 mark and almost the red zone, but in the morning when the engine is still cold it takes about 12 minutes for the needle to reach almost the red zone. I noticed when it's overheating while driving the needle would go down a bit only, but sometimes it wouldn't. Strange indeed. I suspect it is the cooling fan clutch, but the day I had the thermostat and water pump replaced the mechanic told me the fan was fine. Hmmm. This is mind boggling. What should I do?

[Massimo]

Usually a speratic temp guage is air getting into the system somewhere. If the fan clutch failed then the guage would slowly go up while sitting at the lights but would go down while driving.

Check all your hoses including heater core for leaks.

[Learning]

Well, I believe I was ripped off the other day replacing the water pump and thermostat. Spending money unnecessarily. I went back to the same mechanic who tested and stopped the turning fan with his hand. The fan clutched was replaced and my car is not overheating now. I told the mechanic 'I wished you would have tested the fan the other day. We would just have to replace the fan clutch.'

Next time, I will have to be very careful with mechanics. Any suggestions on how to deal with mechanics?

[Simon S]

Any suggestions on how to deal with mechanics?

Research. Buy needed manuals and tools. DIY. Circumvent mechanic altogether.

[Massimo]

Well, I believe I was ripped off the other day replacing the water pump and thermostat. Spending money unnecessarily. I went back to the same mechanic who tested and stopped the turning fan with his hand. The fan clutched was replaced and my car is not overheating now. I told the mechanic 'I wished you would have tested the fan the other day. We would just have to replace the fan clutch.'

Next time, I will have to be very careful with mechanics. Any suggestions on how to deal with mechanics?

Do it your self.

Mechanics arn't isn't always going to be right and that is going to cost you. They can't trace every issue to the cause using the usual method, otherwise you will be spending $$$ on just trying to find the problem. So they use there knowledge, to resolve the issue quickly and cost effectively. Unfortunatly sometimes it is not right and that is just they way it is.

Like I said a speratice temp guage is usually a sign of leakage, not a fucked fan. So if I was your mech I probably would have do the same thing.

[Learning]

Now after driving for 9 days since replacing the fan clutch my car is overheating again! However, this time the temperature gauge only reaches the 3/4 mark when I stop at a red light or when I'm in slow traffic. When I drive at a normal speed the gauge moves down to slightly pass the 1/2 mark.
When I open the hood while the gauge is at 3/4 mark I notice there's a lot of steam pressure coming out from the plastic reservoir tank.

Actually, the other day when I just had a brand new fan clutch put on, I test drove the car and it was still overheating. I stopped and and then the mechanic opened the reservoir tank, looked inside it and next with the engine still running he poured in more coolant although another mechanic already had added enough coolant before that. It fixed the overheating. I wonder why? Was there any air bubbles trapped? Why did he looked into the reservoir tank? What signs was he looking for?

But now, after 9 days of driving, the engine is overheating again moving up to the 3/4 gauge mark.

Please shed a light.

[Komzorz]

Is it low on coolant again?

[dnguyen1963]

Your mechanic does not know how to properly bleed BMW coolant system. Learn and do it yourself.

[jlevie]

My suspicion is that the pattern of overheating damaged the head gasket (or head) early on. Since then every time the car is driven air is being pumped into the cooling system, which eventually causes the engine to overheat. That will also cause a loss of coolant from over pressure.

One easy, DIY, way to see if this may be happening is:

With the engine cold, remove the cap from the reservoir to release any pressure and top up the coolant if low. Then drive the car some, but don't let the temperature gauge go above the 3/4 point. Park the car and once the engine is cold see if the radiator hoses are hard. That would mean that they are under pressure and the only reason for that would be that air has been pumped into the cooling system. This isn't a definitive test but if you find hard hoses you can be sure that there is a head/gasket problem.

The definitive test is to pressurize each cylinder for several minutes with 150-175psi with the expansion tank cap off. A rise in fluid level or bubbles is proof of a leak. A negative result on a cold engine requires that the test be repeated on a hot engine.

[Learning]

Jlevie might be right.

I just came back for my mechanic and he said it was the head gasket 100%.
I mentioned Jlevie pressure test on each cylinder to the my mechanic but he said the definitive test would be to take the car to a smog test station and to see the test result if there is any combustion leak. And so, my mechanic would be taking me to his friend's smog test station to get my car tested. I will let you guys know the result.

My mechanic told me if it was a head gasket problem, it would cost me $900 to replace the head gasket and I will have to leave my car at his shop for 2 to 3 days. Is this price and time needed to repair about right or am I being ripped off?

A brief history of my car before this issue happened:

Months before this issue started happening, my dashboard temperature gauge from time to time would move erratically from 1/2 mark to 3/4 mark back and forth. When I hit the dashboard above the gauge hard with my hand, the gauge would move back to the normal 1/2 mark. So I thought it was the temperature gauge not functioning correctly because of age. However, after having brand new thermostat, water pump, and fan clutch installed, now when the car is overheating showing the gauge mark at 3/4 mark or more and I slapped the dash board on top of the temperature gauge, the needle gauge wouldn't move back to normal 1/2 mark. Thus, I sense that my temperature gauge is not malfunctioning as I had previously thought.

For you knowledge: the expansion/reservoir tank had a leak right in the middle when a pressure test was done on it. Because the leak is in the middle I haven't bothered to replace it as I can still have coolant filled into it up to 1/4 height from the bottom. I was driving with this condition for many months with no overheating problem until an overheating problem came up very recently. I've always maintained the coolant level in the expansion tank at 1/4 mark from the bottom.

Addition: I just thought about this: I suspect the radiator is bad or clogging up as I've had it for about 7 years and it has never been flushed. The difficult thing is how do you know or find out if a radiator is clogging up? How do you test it?

What are your thoughts people?