I think this is a hydro flow question as much as anything, and/but/so...
Not an unusual circumstance for E21s to have the issue of the t-stat not open and the lower radiator hose be cold to the touch while the upper half will leave blisters on your fingers. On a stock system. With seemingly everything replaced and new.
It has been said air in the system causes this, but I don't know that it should prevent flow that much? Thus the question.
And it may be peculiar to that goofy BMW dual path system.
For reference, the e21 (and similar, 2002's run the same thing) water pump has an outlet to the external t-stat, and that sits roughly way between the top and bottom of the cooling system inlet/oulets.
Before the t-stat opens, it runs on the upper circuit. T-stat opens, and it goes to the full circuit, pulling from the bottom of the radiator.
Except it doesn't. No leaks, t-stat functions (when hit with hot liquid). Water pump moves liquid, seemingly well (I've watched it push water with the rad cap off).
How much air in the system would prevent it from moving enough liquid to hit the t-stat with hot water?
Find someone with a vacuum filling device.
I'm 62, a journeyman mechanic, owned my own shop for 35 years, and every time I look at a BMW cooling system, I'm totally unsure how fluid goes anywhere. I think the one from the 4 cylinder E30's that seems to want to bleed the air out of the rad from the bottom is the winner, though.
In reply to Streetwiseguy :
I'll have to look that up!
Not heard of that before, new possibility.
Not my engine, but, pic, for reference
I can't tell you for sure what's going in your case on but the way I get the cooling system bled on my E21 is to jack the front of the car up and run it. The M10/that cooling system seems to be very good at trapping air.
AxeHealey said:
I can't tell you for sure what's going in your case on but the way I get the cooling system bled on my E21 is to jack the front of the car up and run it. The M10/that cooling system seems to be very good at trapping air.
Did that, didn't seem to help, so I'll ask how high you jacked it, how long did you run it?
Fair to say you've experienced the cold lower hose/ hot upper hose phenomena?
Get the nose as high as you can, and squeeze the radiator hoses while the car is running (wear gloves). Another trick is to crack open the top of the system by unscrewing the temp sensor on the water neck that exits the cylinder head.
In reply to 02Pilot :
I'll do it again, doing those things. I'll also re-tighten all hose clamps, including back of the motor/heater core area, etc.
I'd theorize if there are no leaks, it shouldn't suck air from anywhere, right?
If that still doesn't work, any thoughts as to where the glitch in the system is with no (obvious) leaks?
In reply to ГУЛАГ мальчик УР следующий :
It's been a while since I was deep into that system, but it's clearly prone to air being trapped, and a bubble anywhere can cause all sorts of problems. Since you tested the thermostat, you eliminated the one potential part failure that can cause problems. You do have the heater core fully open, yes? I doubt you're sucking air in; more likely there's just a bunch trapped in there somewhere. Squeezing the hoses helps to dislodge bubbles - leave the radiator cap off while it's heating up so it doesn't build pressure.
In reply to 02Pilot :
I'll give it another whirl doing that.
02 FAQ a dude burped the t-stat specifically, and I know that for sure is at least a part of the issue.
