M2 cooling challenge

[allbim]

I agree with mlytle. A large temperature gradient from the inlet to the outlet of the radiator is caused by slow or no coolant flow.

How can it have anything to do with the fan, when the outlet temp of the radiator is low compared to the inlet. In other words, if the outlet is cold, then the radiator and fan are working.

The problem is that there is not enough coolant flowing to keep the engine cool.

Typical temperature drop at idle (as measured by me) from inlet to outlet, with the thermostat open and air flowing through the radiator is 10 to 20 deg F.

[ray_]

At operating temps you should be able to see the water flow with the rad cap removed. Rev it a bit when looking.

Safety glasses, etc...

GL,

[jimk]

Based on my working life of 35 years in the power plant design business my take on the heating/venting troubles follows. I also am doing my homework for an S14 install and have looked at as many photos of install as I can scrape up. I don't agree with some of the things I see.

Is the vent from the head routed continuously up towards the radiator (i.e. no high loops in it)? If not it can trap the air from high point in the head from moving to the radiator. There isn't enoughj pressure differential between the head to the radiator to move an air bubble out the vent tube if it is high looped.

On the E30 installation the air vent goes to a small pipe that is sloped up towards the head tank (car guys call it the expansion tank). On an M10 the water outlet is in same location as that vent nozzle and so has needs no head vent.

Any air that was trapped in the lower radiator hose below the thermostat is immediately sucked in the pump when the thermostat opens and the air ends up in the head on the S14, it won't go out the water manifold on the engine exhaust side because that side is lower .

Also air vented on initial start may not be all there is. Cold water holds air in solution, that water when heated gives up the air. So more air is vented later.

[Ian]

I think jimk might be on to something. How did you vent the S14 head? On my M2, the vent from the head joins the tube feeding the radiator inlet with a Y-tube. While this hose is technically lower than the head, I think the flow of liquid into the radiator acts as a vacuum to pull any air bubbles out. I may have the physics wrong, but this hose arrangement was recommended to me by Pete McHenry 18 years ago, and I have never had problems bleeding the air out of my M2 cooling system, or with overheating. The hose is marked with the yellow arrow in the pic, although the join with the main line is hidden in the pic by the distributor.

[M3M3]

you can see in his engine pic the head vent goes direct to the top left of the radiator...not to the coolant inlet hose like all the rest of the installs not using an expansion tank do.

he has air in there somewhere. symptoms are identical to what i had on first startup. i could squeeze the mid-lower hoses and tell there was no coolant down there. mine was solved by repeatedly pumping all the hoses as the car warmed up. i could see the air get to the radiator when the level would drop. eventually i could see good flow with rad cap off and all was good after that.

[Ian]

you can see in his engine pic the head vent goes direct to the top left of the radiator...not to the coolant inlet hose like all the rest of the installs not using an expansion tank do.

You have better eyes than I do! But I agree with your diagnosis, doctor. It sure sounds like air. When I bleed my M2 I jack the front up and run it with the radiator cap off, to get the coolant temp up quicker. Then the thermostat opens, the level in the radiator drops, I add coolant, then check all the hoses for air before putting the cap back on the radiator.

[jimk]

I also see his vent line under the fuel return hose, it may be ok, but it has a slight high hump in it. It doesn't look to pose as much a problem as Ian's (sorry Ian, it's my observation). I have a friend in CA that has a connection on the upper tank too and I prefer it to the connector in the main return hose to the radiator.

Marshall, I agree that from your photos of the lower hose, it will be full of air and needing purging, but that is a difficult space to arrange without a bubble trap.

Back to the vent hose. If it is slopes down instead of up, then there has to be more waterflow resistance in the head outlet/water manifold than the elevation drop in the vent hose to make any air exit thru the vent. If the hoses were clear plastic and one could see the air bubble, it would be much easier to explain.

Anyway the problem install doesn't seem to have a troublesome vent hose.

Ian there is no vacuum to suck at the radiator. What is removed from the radiator is replaced by the returning flow. The inventory of water is constant.

[Ian]

It doesn't look to pose as much a problem as Ian's (sorry Ian, it's my observation).

No problem. You have provided ample justification for my new groovy aluminum overflow tank Which of course, I will mount higher than the head!

[M3M3]

ah crap...if you are putting in a groovy shiny overflow tank, i may have to install one too! ;-)

Jim- yes...not a lot of space in there for s14 tstat with its odd inlet/outlet angles....end up with hose config that is not optimal.

[Ian]

ah crap...if you are putting in a groovy shiny overflow tank, i may have to install one too! ;-)

We're all a bunch of enablers!

[allbim]

Have you tried the vacuum cleaner trick yet? It takes a couple of minutes and costs nothing. It's just another way of burping it.

[teeb]

Merci beaucoup Dr. Vyse for your logic and reminder to not assume. I have NOT given the thermostat a warm bath to see if it opens. I’m a bad, I know. I assumed, since it was new. I will add that to the list to check to BE SURE.

Dr. Marshall, oil cooler location might be OK…this is a relief not to have to move it as we custom cut lengths…etc. I have tried to show images of the lower intestine that you requested. As you can see, bowels can be messy to get to, especially from China. As you can see in the x-rays, I can’t quite get a clear image of the very bottom hose. I would say the angle on the lower hose to thermo has a 120 degree bend with a slight, very slight, kink. So slight, it slipped into the “not the problem” category in my mind. But now that the child has a fever, that has re-surfaced to consciousness. Treatment suggested? As I did not shorten the aluminum return, I struggle with angles, as you well know. I may try another set up to ease the bend/kink more, but the aluminum return determines a lot in this situation.

Dr. Blaz Downwhillwolf, your diagnosis and suggested treatment may also be a good idea...leaning radiator and back-mounting the fan. Obamacare only affords me to cut or re-direct hoses. I like the thinking and need to look at the space with the oil cooler in there.

Dr. Allbim, thanks for the radiator differential temperatures. Seems logical to me that a bent-bowel down low might be the culprit. It would also seem that choking the flow may create cavitation at the pump, right? Wouldn’t the low pressure draw cause that?

Dr. Ray Koke, I did rev the engine and it “seemed” to agitate the waters noticeably and with my safety glasses off, I noticed the temps responded quickly as per by finger-test temperature.

Dr. Jim K, the head outlet hose, as you might be able to see, is not plumb into the T fitting that traditionally crosses from passenger side to driver side and returns to the radiator. When I had the radiator built, I had it plumbed into the top left of the radiator. I’m not sure if a pressure gradient exists that would deny the air passage back into the radiator. While it seems to flow uphill, does pressure lock it out? Your concern about feeding the head return line into the larger return hose makes me wonder.

I excluded the expansion tank, which I understood to be the part of the system that allows for thermal expansion improving efficiency of cooling capacity. Does it matter?

Dr. Ian, I will error on the side of air…how do I determine if there is air? I’ve seen the radiator level drop after getting up to temp on the first warm up. And it still overheated…

Funny how more answers bring up more questions. With that, I have a laundry list of the things to eliminate or try.

My thanks to a great team of doctors!

FYI Marshall – Do you run VIR? June BMW Tarheel this year would be a fine venue to buy you a beer and chat M2s. Not to mention, I’d love to see your wet cat run!

[M3M3]

here is my original configuration with the IE radiator. i have simplified it a bit since i put the silicon garage custom rad in.

yes, i run VIR. one of my favorite tracks. mainly run at summit recently.

[jimk]

--we experienced dramatic temp differences from the top of the radiator = 230F compared to the bottom and 65F. I wonder if the position of the oil cooler and air flow from the fan might somehow relate? See the pic? The cooler is positioned at the top of the radiator....hmmmm??

OK, so relocating the remote oil cooler will be the first test! I feel good about this one....

Thanks all!!!!

Where was the temperature taken on the radiator? I ask because I think I see both the upper and lower radator hoses on the right side of the radiator. You can get "short circuited" water flow thru only the section of tubes on the right side of the radiator, thereby not get full use of it's cooling capability.

Also as a side note: The thermal valve in the oil filter head is the same as on an IX and opens at 190F oil temp or so to cycle oil thru the cooler.

[Ian]

Where was the temperature taken on the radiator? I ask because I think I see both the upper and lower radator hoses on the right side of the radiator. You can get "short circuited" water flow thru only the section of tubes on the right side of the radiator, thereby not get full use of it's cooling capability.

Unless it is a double-pass radiator, where the top and bottom sections are partitioned off.