Yet another coolant bleeding question. (long)

[Kristuphir]

I've searched a lot on this, but wanted some reassurance (or the opposite, if necessary).

I bought my car recently (91 535i 5-spd) and shortly thereafter noticed a fairly substantial coolant leak at the big hose that comes out of the thermostat housing (lower radiator hose, I'd call it). It'd drop a small (5-6 in.) puddle on the driveway over a couple of hours. Over a couple of weeks, I needed to refill the reservoir twice. Temp gauge never wavered from just a hair under halfway.

So this weekend, I was sitting at a stoplight when the temp chime went off. ****! In the process of pulling over (within the block), the needle dropped to normal. OK...fan clutch? Started heating up at another light (but by now I was watching it, and it didn't go over 3/4), then dropping quickly down. Got home, did some searching. OK, with a leak that size I'm letting air into the system, needs to be bled, obviously needs to have the leaky hose replaced. So I bled it, it ran fine at the right temperature. I ran down to BMA and got a hose; everything was good. Took a 20-mile trip on the freeway; everything fine. Sitting at a light after the freeway, I watched the gauge go up quickly to about 2/3, then drop of its own accord. Solid ever after, including on the whole trip home.

Sunday comes; i drain the coolant (not a hint of oil in it; also, not a hint of steam in the exhaust, and I've been looking with an eagle eye after what I've learned about head gaskets on these cars; also, changed plugs a week ago and all the old ones looked fine), replace the hose (PO replaced thermostat a couple months ago), get the car on ramps, add coolant and bleed as per instructions on Bruno's site and elsewhere (same way it's done on my old E30). Bleed, bleed, bleed, refill, bleed bleed etc. Get all the air out that's coming out. Car will idle in the driveway til the cows come home with rock solid gauge.

One thing I noticed while doing this - I could see water being thrown around by the starter ring gear through the little hole in the bell housing. After the requisite freakout and search to find if water was pouring out of anything into that area, I realized it was only happening right after I bled the system. I decided that water was running down the underside of something (car's still on ramps here) and ending up in that most disturbng of places. Sure enough, when I took it off the ramps and for a drive around the block, i came back and it wasn't there anymore. The clutch was wet too, it was jerky like when you go through too big a puddle, and that went away too after driving a little bit. Also, the car wasn't using water that I could tell.

So we take it to run errands last night and it's fine - gauge never budges past halfway. It sits overnight, I take it to work this morning, everything is normal. I get in tonight after work, everything's normal driving around town. Run an errand, car off, car on, run another errand, car off, car on, leave the parking lot, then POW, temp gauge making a dash for the red! Car off! 8mm wrench out of my pocket for roadside bleeding (yeah, after all the horror stories I read, I wasn't trusting it to be perfect yet!)! Spit, spit spit, then just coolant, take a look inside and the gauge is like nothing ever happened. Stay on surface streets the whole way home, but I have to stop every mile or so and repeat (I just pull over any time the gauge even edges over halfway, because I know where it's going). Every time there's immediately some air in the system, steam and nothing spit out for a few seconds and then just coolant, and temp gauge drops immediately. It happens sitting at stoplights; then it happens accelerating from stoplights. Then it happens at 30mph and as soon as I pull over the gauge drops without my doing anything. Then...you get the picture. The fan seems to be doing what it's supposed to all this time - if it's hot, it's spinning hard, making noise, and changing my hairstyle with all the wind it's generating.

So as much as I adore bleeding the cooling system on the side of the road in the rain every two miles, I think I need to figure out: is this just classic M30 air-in-system-after-flush madness, and I just need to bleed and bleed and bleed some more, even though I've done it 15 or so times? Why the 40 or so miles last night and this morning that were just fine and normal? Do I have someplace where air's just pouring in that I can't find? I haven't seen any leaks other than the one I fixed. I don't think I'd like to blow the head gasket or warp the head at present; if I can get it to run forever at regular temperature in my driveway but can't drive it without an eye pegged on the temp gauge, what do I do? Am I concerned prematurely here? I now fully believe all the people who say how finicky the cooling system on this car is.

OK, off with me to eat my dinner and bleed, bleed, bleed. Thanks in advance to anyone who made it through this very long question about something that everyone's probably tired of thinking about. Apologies for any details left out - ask for them if you need them.

[Blitzkrieg Bob]

make sure it's contacts are clean and dry.

Test it with a meter to make sure it's working.

It does not sound like "sharking" the car only cools when it's moving, which would lead you to suspect the fan clutch or pump impeller.

Trapped air would heat up at idle....I know, sent hours fiddling around after a coolant flush. And if it did drive, the expansion tank level would drop as the coolant replaced the air over a few days of driving.

[Kalevera]

The late M30 cooling system is easy; much simpler than most people make it out to be. After dealing with my share of cooling system problems, observing how others cause and fix theirs, I've concluded that it usually boils down (haha) to operator misunderstanding or error. 99% of the time, it takes me less than two minutes to bleed and prime an E34 m30 cooling system.

Here's the quick and dirty way to determine if you've got a mechanical or electrical problem: the next time the gauge hits the red, shut off the car and open the bleed screw. The coolant should be boiling. Anything above 1 or 2 o'clock on the gauge and the coolant will boil as it leaves the bleed screw (usually foaming, or worse). At the 3/4 temp mark, you'll hear the mixture boiling in the hoses with the system closed. No boiling coolant? Read Bill R's posts on coolant temp sensor replacement, also consider the dash caps (just a thought).

If it is indeed boiling, pull the thermostat and make sure that it's correctly installed and that it's a reliable brand. A person fixing a car to sell it doesn't have much incentive to buy expensive, good quality parts.

best, whit

[Kristuphir]

Whit, I've not been on the board long but through my searching on a variety of things, you've been most helpful. Just wanted to express appreciation.

When the gauge goes high, it seems like I usually get the boiling water you describe. When I open the valve, it spits and steams and foams and sounds boily. Checking the temp sensor is a simple thing that I should've done anyway, though. Tomorrow night, methinks.

Well, so I went back out there, refilled the reservoir, started it up, bled it (there was a little air spitting out of there), let it run, then realized I'd forgotten to turn on the heater. So I did that and...no heat. That's funny, the heater worked when i was bleeding it yesterday...I put my hand on the heater valve and it was silent - none of the usual vibration mine makes when it's on. So I bled it again - no air came out, but the heat came on and the heater valve started its happy little dance. Took the car for a spin - around the block, onto the freeway, to a stop, through a series of traffic lights, then pulled it over, let it idle for 15 minutes, pulled away, went home, let it idle...nothing. All was good. This was with the heater on...bled it one more time, no air, went for the same drive again, all was good.

So I'm back where I was last night...keeping my fingers crossed that I'm done. Although you're right, it would be a good idea to replace the thermostat again...only then I'd have to go through all this once more. But peace of mind...do you recommend drilling the hole in the top of the new thermostat, like I've read here?

is there even such a thing as an expensive thermostat?

[ChefJRD]

I've got an '95 M50, so I'm not sure how much this relates, but your situation sounds very similar to one I had when I first got it a little over a year ago. The engine would run fine for the first 30 minutes or so of driving, but then spike to the red for a bit and then drop back down to normal real quick. I bled the heck out of the system, but that didn't seem to help. Reviewing old repair records, the oldest thing in the cooling system was the water pump. When we got the pump out, it was cearly the problem - the impeller had cracked off from the shaft. Put the new pump in, new coolant/water, bled the system and it worked just fine.

Like I said, I'm not sure how applicable this is for the M30, but it was a huge relief for me when I finally figured out what was going on. I hope this helps, good luck.

[Kristuphir]

Well, it's certainly an option. The car was rock solid on the way to work this morning (20 or so miles in all types of traffic and speeds)...fingers crossed that it will be tonight too, but if not, it'll be time to change everything i don't know is new...

[Kristuphir]

Well, it's been two days of normal driving after that last bleed, and everything's rock solid. Guess it was just one of those things...hopefully next time I'll be going the 2-minute route

Thanks guys...

[Kristuphir]

Well, after almost a month of commuting and an 800-mile road trip, I got the high gauge again today. I'm at work and this happened just a block or two away, thank goodness. At lunch I'll take some water out there and fill 'er and bleed 'er again. Up til this point everything has been PERFECT temp-wise, and trust me, I've been watching.

I do notice the occasional, briefest whiff of coolant smell. So I must have another leak, right? And that would be slowly letting air into the system, right? I get no fog/smell when I turn on the heat or defrost, so I'm *assuming* it's not the heater core. I've looked around quite a bit, and have yet to find another leak. What are some other weak spots besides the t-stat hose I already replaced?

Would it be possible for the system to be letting in air while not letting out coolant?

[Javier]

it is a tiny hose running from left top of radiator to left side of expansion tank neck. It may get clogged and cause overheating. There is a nice write on this issue in Bruno's site, at the bottom of this page.

If cars overheats, it can burp coolant and you'll smell it.

Javier

[joshua43214]

It is possible but unusual to leak air in but not coolant out. Normaly this is caused by a loose hose clamp. The rubber swells enough when warm to seal, then as it cools down, in shrinks and allows air to be drawn in. Normaly it will have signs of seeping arround the clamp. look for crusting and the like arround the hose ends and other coolant seals, like the T-stat cover. I have found that it is good maintainance practice to retorque all the hose clamps at every oil service. Just use a swivel socket and loseen every clamp under the hood 1/4 turn and then tighten it back up a bit. Do this with the hoses hot, and don't over tighten the clamps, they take very little force to clamp properly.

While you are rooting about under the hood, verify that the radiator is clean of leaves and other obstructions, tip it forward if you can to look between the radiator and the condensor, alot of buggy temp problems are caused by debris.