Bottom hose cold, radiator cold. temp needle swings to right very quickly once it starts to move.

Never reached red while I was testing it. My wife, who was driving it at the time, promised me it never hit the red (though we lost an 86 this way, and she might have been afraid that I would have blown a head gasket). No water in oil.

Any other way to test if the head blew?

This happened after a 45 minute/20 mile ride. Could it just be the thermostat? Or is it the water pump?

A heater hose (i think) next to the firewall busted and was blowing steam. I cut it (the hole was just next to the clamp) and reattached it. I assumed that was just a result of the heat and not the cause of it, though I read that I could have air in the system. Any ideas?

if you are losing coolant at a slow and steady rate, then chances are good that your head is warped and or your gasket is leaky. I doubt you BLEW the gasket or damaged it for that matter. because if you did the car would run like absolute crap and also because the temp didnt get in the red. best way to find out is to have a leakdown test done, in which the coolant system is pressured up to a certain psi. then simply see where the fluid is leaking

Is top hose hard (pressurized) and hot?
check plugs. is one or more clean?

Bring it to an indy. If they're equipped like we are they'll have an emissions tester that can read Hydrocarbons. Warm the car to operating temp and open the radiator cap (be careful not to be burned) and have the shop use the emissions tester to sniff the radiator for HC. If there's more than 3ppm then odds are good it's toast.

I've seen a couple M50s that were destroyed because of failed water pumps (M20s I dunno); you may be taking a greater risk than you might think by driving it.

There seems to be some pressure in the top hose. I'm pretty sure that head gasket is ok, though the radiator has needed to be topped off once a month or so. Been that way for four years.

The real question is: Could it be the thermostat? I'm planning on trekking out to where the car is stranded tomorrow. I can change the thermostat on the spot, but not the water pump (due for the timing belt change anyway). Am I wasting my time? Should I just call the tow truck?

Thanks

Did you check that plastic radiator for cracks and any coolant leaking from anywhere?
While you check on thermostat might as well check your clutch fan , water pump hoses, and hoses(all the plastic GOODIES).

I would say its a good possibility that it is the thermostat. Especially if the car is heating up so fast and you are not getting any heat or circulation in the radiator. It could be the water pump, but generally when water pumps go they leak and make noise. Besides, in my oppinion the thermostat is easy enough to replace and cheap enough, so its worth a shot to try and avoid the tow bill.

You have an M20, so anytime you lose coolant you'll need to bleed the system to clear the air pockets out of the head.

bleed it, top if off and bleed it again.

i'd start with a thermostat if anything, but you need to know if the water pump is circulating water. then a good bleed job. those engines are a PITA to get all the air pockets out.

Could be a leaking heater core. Leaking in the heater box and out the water drain.

Well, I just replaced the thermostat. No difference. I let it idle, it stays cool, but once I drive it, it heats up very quickly and I have to shut it down. I don't think it would make it a mile.

It is not leaking, far as I can see. It does make noise, but not consistently. It had been shrieking when we started it--but it did that occasionally ever since the last timing belt/water pump job 3 years ago (50k). It was especially bad when we first had it done (I thought it was the actually timing belt...maybe getting broken in or something--but since I've been reading some other threads, I think that's wrong. I suspect it was the water pump all along).

I can't imagine that air in the system would cause it to overheat so dramatically. But it did have a busted hose going into the firewall. The radiator never gets hot.

I'm getting it towed. It's time (maybe a little early) for the timing belt to get replaced anyway. I could just drive it to the mechanic close to where it's stranded--not a BMW guy but seems capable, but think I'll just pay to get it towed all the way to the (expensive) specialist.

Anything else I should know? Looks like it will cost about 500. Sound right?

Thanks

Had it towed to the good mechanic, feeling pretty good about that. Not feeling good that he told me that it looks like a blown head.

Said he'll tell me for sure tomorrow, he ran out of time today. Says he has to get the air out of the system.

My questions are these: what exactly would you do to test the head? Is it worth it to get a second opinion? Does this air in the system theory make sense as a cause for this early (hopefully false) diagnosis?

I would appreciate any insight and/or sympathy and commiseration.

I interrogated (not just asked) my wife about how it went down. She said she saw smoke, but the needle stayed at 12. She drove it a mile, parked it, more steam, needle started going to the right, never to the red. That's her story and it's held up under cross examination.

Heater hose was blown when I found it. That would explain the steam (I think) without the overheat. It would also explain excessive air in the system. The ruptured heater hose could have been the cause and not the symptom after all.

Thanks. Let's all pray tonight. I love that car.

Good news--the system just had to have all the air bled out of it. I'm pretty amazed that that's all it was. The water pump is fine, pressure is fine, it just had air pockets--probably from the burst heater hose.

I drove it up to 90 today, had it out for about an hour. Temp never went past half way.

I'm going to drive it for the next week, then take it in to get the timing belt done.

Thanks for all the help.

Still okay??

Good news--the system just had to have all the air bled out of it. I'm pretty amazed that that's all it was. The water pump is fine, pressure is fine, it just had air pockets--probably from the burst heater hose.

I drove it up to 90 today, had it out for about an hour. Temp never went past half way.

I'm going to drive it for the next week, then take it in to get the timing belt done.

Thanks for all the help.


Thanks for the update!

Same thing happened to me this week. I found that the throttle body heater gasket was shot and slowly leaked. Bypassed the throlttle body, bled thye system of air and runs fine.

I can't believe how sensitive these systems are to air.

I have been chasing an fluid leak forever.

1. replaced expansion tank (no lift and thought the leak was a crack)
2. replaced radiator (figured age killed the rad somewhere else or I did with the tank replacement.)

Then realized it was the heater hose. (lower hose on driver's side above coolant level sensor) that just would not tighten enough and was giving the slight leak. The previous owner just replaced that hose less than a year ago according to his records so I would have never thought that new hose was the problem.

Lesson 1: When buying a used car, just replace all disposables and don't assume that the maint. records are correct (or that they used OEM parts).

Lesson 2: I always used to operate by the rule troubleshoot from least $ to most $$$$.

Lesson 3: Nothing beats OEM parts. In some cases aftermarket items are fine but cheap parts that look OEM can be more trouble than they are worth. I try to never use chain store parts for certain engine items because they seem to be hit or miss with my BMWs.

Autozone / Advance Auto / Pep Boys can't seem to even provide the correct belts for our cars. So outside of plugs, some fluids and items for emergency repairs, I tend to stay away from them.

Now I have a better list for troubleshooting overheating and know to check for air in the system first.

Thank you