Overheats after driving for an extended amount of time.

I have a 92 BMW 735il and it continues to overheat after I have been driving it for an extended amount of time? (1-2hrs.) All cooling components have been replaced:

Radiator
All the Hoses
Water Pump
Thermostat
Fan Clutch
Reservoir cap
Fan-switch sensor

On my last trip I started to overheat, so I pulled over and turned the heater on, but only cold air was coming out. So I open the hood and felt the hoses. The outlet was hot and the inlet was cool. Now, I know the thermostat is good because I tested it before I put it in. Once I released the pressure from the system the coolant in the reservoir drained into the engine and the cooling system started operating normal, as did the heater.

Is it possible that after driving it for a while it is getting air into the system, which is causing my overheating problem? If so, where could it be coming from? All hose clamps are tight. I do notice that when the heater is turned on initially I can smell a hint of coolant. Also, Is the External water pump only supposed to come on when the heater is turned on?

Was the system properly bleeded after all that work was done do it. That could cause your overheat problem.

No it wasn't. So I did bleed the system properly using the bleed screw on the thermostat housing. It appears to be ok for now, but I'm very skeptical of taking it on long trips. Any other ideas?

Thanks-

just drive around alot close to where you live. Dont go farther then 5miles or so if you want to be sure about it.

Will do.. Thanks adgain.

Ok, so I had it idling for 2 + hours with the ac on and it stayed in the middle. I took it on a drive about 45 minutes up hills and straight open road, and it did well. Then I checked it on stop and go traffic, about 4 or 5 stops after the fifth stop I was home and I let it sit in drive for about 10 minutes and it got about 1/8 inch pasted half way and stayed there. I could hear the electric fan on, but it didn't cool it down enough.


Do you think I could have gotten a faulty fan clutch?

Well, I've just developped a similar problem over the last week on my 1990 735i. :( Today it overheated really badly and I had to have it towed to my local garage (which is obviously closed for the weekend, D'oh!). The AA (Automobile Association) mechanic said he suspected that it was the thermostat. As you've recently had yours replaced could you tell me how much I am likely to have to pay. I'll let you know if my garage mechanics find anything more sinister on Monday. Maybe that will offer some clues to your problem.

I replaced the thermostat myself, so it didn't cost me any labor. The thermostat itself was only $20.87 plus coolant. The grand total was 35 bucks. I've seen the oem thermostats cheaper online @ www.bmw-parts-direct.com, along with other parts.

Good Luck-

Thanks dlog. takes a little weight off my mind assuming that my AA man was right. If he wasn't do you have any ideas what might be the most likely cause of my overheating. The mechanic made his judgement based on the fact that while the coolant was boiling, the hoses in to and out of the radiator were cold. Do you think that makes sense or am I likely to be looking at something more sinister?

If the thermostat has never been replaced it a good assumption. It’s sounds like a flow issue. It could be a water pump, but those generally will make a bunch of noise and leak a good amount of coolant out of them when they go bad. You could also have a restriction in the lines somewhere. More specifically the line going from the expansion tank to the radiator. All of this a good mechanic will check and shouldn’t be that expensive to do so. But what is expensive is a blown head gasket. :(

These cars can be a real pain in the butt for getting the air out,

It often helps to have the front of the car slightly higher.

Another problem area is the flow return to the expansion bottle, with the expansion cap off you should see a steady flow of water bact to the bottle. If not remove the home and clean with a pin.

Flush the radiator & check the viscous fan, (use a rolled up newspaper and a warm engine - you shouldnt be able to stop the fan - watch your fingers)

Alright thanks for your help. I drove the car around and got it nice and warm. Used the rolled up newspaper and stopped the fan from spinning.

If the thermostat has never been replaced it a good assumption. It’s sounds like a flow issue. It could be a water pump, but those generally will make a bunch of noise and leak a good amount of coolant out of them when they go bad. You could also have a restriction in the lines somewhere. More specifically the line going from the expansion tank to the radiator. All of this a good mechanic will check and shouldn’t be that expensive to do so. But what is expensive is a blown head gasket. :(Well, I got the news I had been dreading from my garage today: although the overheating problem might well have been contributed to by an inoperative viscous fan, they said that the head gasket needs to be replaced! :shakehead I had the M.O.T. test (don't know what the U.S. equivalent is. Basically a mandatory annual road-worthiness test) done at the same time as it was about to expire and so I discovered a number of other delights that need to be fixed as well at the same time! Time to part with the better part of £2000.:sadwavey:

Well, I got the news I had been dreading from my garage today: although the overheating problem might well have been contributed to by an inoperative viscous fan, they said that the head gasket needs to be replaced! :shakehead I had the M.O.T. test (don't know what the U.S. equivalent is. Basically a mandatory annual road-worthiness test) done at the same time as it was about to expire and so I discovered a number of other delights that need to be fixed as well at the same time! Time to part with the better part of £2000.:sadwavey:

£2000 how comes ????

It cost me well under a hundred pounds to replace the head gasket on my E32 735.

OK if you are paying garage labour then the bill is gonna be bigger.

What are the other bits it failed the MOT on, might be able to help with some of them?

Let me know where in the UK you are also

Tony

Yeah I'm just curious how much it would cost a shop to replace the head gasket? I'm in the US.. I called one shop and he said thousands and it would cost more than what the car is worth. I called another shop and they said around 2k and that's including if the head has to be sent out to the machine shop for repairs.

So far I pretty sure that its the fan clutch, but I'm just perparing myself for the worse.

£2000 how comes ????Ok, so here's how it breaks down (no punn intended ;)):

Between £800 and £1200 for parts, labour, and sending the head off to be 'skimmed' and tested. They say the cost will vary depending on the relative trauma of the job (i.e., what else falls apart while they're doing it and thus costing more time and money). Bear in mind that the labour charge is £50 per hour plus VAT.

Then I also need to replace the front shocks: £350 (including labour)

Then there's the viscous fan thing which is £150 (including labour)

Oh yeah, and they have to replace one of the brake pipes and the front suspension (3 ball joints, a drag link and something else).

'Is it worth it?' I ask myself. Actually, that's what the guys at the garage said! They couldn't believe that I wanted them to go ahead and do it all. After all, it's probably more than the car is worth.:screwy: The thing you need to understand is that I'm a graduate student and that I bought the thing for only £800 in the first place back in the summer. I've looked around for alternative cars that I could buy with the £2000 I'm going to spend on this car (that I really like) and can find nothing else that I would want or trust not to have other mechanical problems which would just end up costing me more money in the long run. If I weren't a student, I'd ditch the thing and be able to buy something much newer. But that's a moot point really. If only I had £5,500 I could buy myself a nice second-hand E38. I'll keep dreaming!

(BTW, I live in Cambridge Tony, and this is my 1990 735i SE)

http://img228.imageshack.us/img228/2823/mycar2xu.jpg

Find another garage, sounds like they are taking the piss

I changed the head gasket on my 1990 735 myself, and it took me a day. And I am not a mechanic, I work in IT!
Cost of the parts
Head Gasket set £57.50 + Oil & Antifreeze

Viscous fan £40-62 + 1/2 hr labour

Front Strut insert @ £62.00 each + labour

Brake pipe ball joints etc ?

The choice is yours but you can pick E32's up for not a lot of money, buy one with 12months mot put your wheels on it and sell yours as parts, should return you a tidy amount.

Oh and i'm in Essex

Ok, so here's how it breaks down (no punn intended ;)):

Between £800 and £1200 for parts, labour, and sending the head off to be 'skimmed' and tested. They say the cost will vary depending on the relative trauma of the job (i.e., what else falls apart while they're doing it and thus costing more time and money). Bear in mind that the labour charge is £50 per hour plus VAT.

Then I also need to replace the front shocks: £350 (including labour)

Then there's the viscous fan thing which is £150 (including labour)

Oh yeah, and they have to replace one of the brake pipes and the front suspension (3 ball joints, a drag link and something else).

'Is it worth it?' I ask myself. Actually, that's what the guys at the garage said! They couldn't believe that I wanted them to go ahead and do it all. After all, it's probably more than the car is worth.:screwy: The thing you need to understand is that I'm a graduate student and that I bought the thing for only £800 in the first place back in the summer. I've looked around for alternative cars that I could buy with the £2000 I'm going to spend on this car (that I really like) and can find nothing else that I would want or trust not to have other mechanical problems which would just end up costing me more money in the long run. If I weren't a student, I'd ditch the thing and be able to buy something much newer. But that's a moot point really. If only I had £5,500 I could buy myself a nice second-hand E38. I'll keep dreaming!

(BTW, I live in Cambridge Tony, and this is my 1990 735i SE)

http://img228.imageshack.us/img228/2823/mycar2xu.jpg


Man thats a lot of work. Is there any special tools needed for the job? Did you send your head out to a shop to check for any cracks?

No tools that cant be borrowed/bought

A torque wrench with an angle setting.
A star drive for the cylinder head bolts.
A selection of flexy bars make the lower manifold nuts more accessible, failing this a double jointed wrist or small child do the job equally as well.
If you can get the exhaust downpipes undone you can leave the exhaust manifold on (makes it a bit heavier) but less awkward bolts to undo.
A methodical approach!
The heads rarely crack but can become eroded due to lack of antifreeze.
Or become warped if overheated - check with a good steel straightedge


PS I have a spare 735 head in the garage if anyone needs one!