M52b28 coolant boiling

[Epyon85]

So..

My e30 is fighting me and I'm close to taking a match to it. Whenever I attempt to bleed it up and get it onto the road the coolant simply boils over, I've checked for leaks using a coolant pressure tester and and I appear to be leak free.

The car will get up to temp, after a good hour or so of bleeding I can get it so the car self cools with the electric fan but eventually the pressure cap leaks out and coolant overflows. You can feel the coolant is boiling over In the hoses and it's quite a coolant fountain if you crack open the bleed screw when this occurs, steam and spitting boiling hot antifreeze all over the place.

The level in the expansion tank always seems to rise up no matter how much I bleed the system, the weird thing is the hoses don't feel pressurised when this occurs otherwise I'd be looking down the head gasket route, there's no sign of coolant in the oil or anything coming out of the exhaust. The engine runs sweet and idles a treat, at the moment I really am stumped! So far I've done the following....


Pressure test - pass
Radiator flow and leak test - pass
Compression test - all good


Any ideas?

[Brianmoooore]

Plastic rotor on the water pump broken up?

[Epyon85]

Changed for a metal one when I put it in the car buddy.

[JF008]

I had the exact same thing happen an it was my radiator cap that was at fault.

[Epyon85]

Had the rad cap tested when I had the rad tester and it came back ok. I'll borrow the chemical head gasket test from
Work on Monday and see how that goes, cylinder leak down test after that depending on results.

[fixedwheelnut]

If it isn't maintaining pressure it has to be the cap or a leak, with all the tests you have done so far finding nothing my money would be on the cap

[DanThe]

As above its usually a faulty cap, what pressure was it tested up to?

[Epyon85]

Well the radiator was tested with the existing cap at my local rad specialist, I'm not sure what pressure it was tested to but I know it's a 2 bar rad cap?

[DanThe]

Modern BMWs now use a 1.4 bar cap, I was told recently to use a 15psi cap with a custom made rad but it couldn't hold the pressure so went up to 20psi
Its worth trying a different cap for the effort involved, I've seen some with damaged O rings which will let pressure out

[_Dan_]

M52 should have a 200 cap, 2bar.

What rad are you using ?

[Epyon85]

Yes running the 200 cap, and I believe it's a 36 318 rad.

[_Dan_]

With the tank on the side of the rad?

I've had problems with mine, Ive got a m20 on a e36 rad.

Because the thermostats and expansion tanks are different designs it gives all sorts of problems.

A e36 thermostat has a ball bearing hole in it to allow a bypass of pressure when it's closed.

The e30 thermostat hasn't, it's got one in the expansion tank side.

So I was thinking if you had used the e30 rad it would have potentially give you problems.

[Bela]

Anyone have the part number to order for the 2 bar cap please?

I'm having the same problem.

TiA

[_Dan_]

Ebay item number. 221177893071

[Bela]

Thanks Dan,

I wasn't sure whether that would have been a good purchase, was after an original replacement.

Have you had any experience with one of these?

[_Dan_]

Yea top ran are a good german make, I've got a 140 top ran on mine

[Bela]

Cheers

[Bela]

Sorry about the hijack Epyon85

Ordered an original cap from Cotswold today, will report back once fitted.

Thanks

[DanThe]

I would advise to fit a 1.4 bar cap, as the heater valve/matrix will be a lot less pressure resistant to what it was 20 years ago

[HairyScreech]

What are the E30 caps?
I know there is a cap recall as the early caps are too high a pressure and pop the heater matrix.

[Epyon85]

I'd be interest to hear how I can feel like bogey on mate!

[_Dan_]

The 1.8's use a 200 cap, so the matrix should be the same as a 325i 140 cap car?

[Bela]

Pressures good on my car, cap was weeping away though when inspected last night.

Have had the car almost 5yrs now with the current M52 B28 setup, did the metal impeller waterpump and thermostat 2 yrs ago. I think the seals on my cap have perished now. Lets see how it goes....

p.s. never had a mess in the foot well from blown pipes to heater matrix with a 200 cap in place

[Coopdetroop]

I put a 200 cap on mine and it blew 2 heater valves. Ive swapped it with a 1.4 bar one now from the e30. I personally would recomend the 1,4bar one. The 25+ year old heater valves are proper weak

[Bela]

Pressures good on my car, cap was weeping away though when inspected last night.

Have had the car almost 5yrs now with the current M52 B28 setup, did the metal impeller waterpump and thermostat 2 yrs ago. I think the seals on my cap have perished now. Lets see how it goes....

p.s. never had a mess in the foot well from blown pipes to heater matrix with a 200 cap in place

Didn't check properly but mine is the 140 cap.