Rad problem possibly solved

[oze30]

Anybody else had a problem with blowing the end tanks off the e28 rads? i may have sorted the problem, only thing is, i think i'm the only one who has suffered!! I did it with the M30 and now the M60.

The E28 metal rad is a 1.0 bar metal cap. The M20 is a 2 bar and M10 is a 1.4bar. Both are plastic caps.

So, I'm trying to find the lowest pressure cap possible to stop this from happening. BUT will this have an effect on the engine by running less water pressure?

Does this make sense to anyone else???

[Turbo-Brown]

Guess the boiling point of the water would be reduced, but what effect that would have I have no idea!

That's not very helpful is it?!

[oze30]

kinda.. But if the E28 M5 runs a 1.4bar... I dunno. I just want to stop popping rads!!!

[suzie650]

1.4 bar should be enough... unless yours runs hot (over 95°) which it shouldn't anyway, as the thermostat on m60 is an 85°iirc.

I remember reading about m20 pressure caps allowing too much pressure build up, and being changed for different ones during a service by bmw... Maybe yours is an early type?

It will be better than blowing rads anyway...

[oze30]

I've swapped both rad caps for early late, e30-e34. Spoke to they giuy who's going to have a look at it and basically said that the rad is probably not man enough to cool a V8, so it keeps over pressurising itself and popping the end cap off. Which kinda doesn't make sense to me. Why wouldn't it just vent through the rad cap if that was the case?

[old_skool]

It may just be because of the larger thermal mass of the new engine vs the size of the rad. A smaller rad will have to accomodate a greater degree of expansion because of the larger liquid capacity of the engine.

Obviously the engines coolant galleries themselves do not expand, leaving the work to the hoses and the radiator. Almost wants another expansion vessel putting in to offset the system volume.

[oze30]

but the problem is I was doing this with an E28 rad and M30B35, so I don't know how that happened (possibly blocked gummed up rad??) but the v8 blew a new one!

[suzie650]

the expansion is taken up by the return to... the expansion tank. so that shouldn't be a problem.
You do have a return on the E28 rad, don't you?
But if water gets in the expansion tank (level rising, as it does) the air needs to go somewhere from a certain pressure on.

I can only think that the E28 rads must be quite sensible to overpressurisation, and as it's the weakest point in the system due to your 2bar cap, it blows instead of letting a bit of the pressure off the expansion tanks cap. I'd go with the 1.4 bar and give that a try. (Highly unlikely that both your engines were pressurising the system through the HG...)

[oze30]

I'm waiting to hear back from the guy. If he can mend and re braze it all , then cool. I have another rad to play with. If not, He's going to try and source a different one. He had a nice tractor rad in there. about an inch thick. That would work!!

[Gunni]

140kpa is the now standard cap from BMW for M20´s

you should rather be overheating and not blowing caps or rads,.
the system normally only runs close to 0.9-1.1bar.

I think your expansion cap is not working if the rad is bust.

[oze30]

140kpa is the now standard cap from BMW for M20´s

you should rather be overheating and not blowing caps or rads,.
the system normally only runs close to 0.9-1.1bar.

I think your expansion cap is not working if the rad is bust.

Yes but a 540 cap is 2 bar and the E28 535 cap is 1.4 bar. See the dilemma?

[suzie650]

put a 1.4 bar cap on it. won't affect the engine. (actually, probably even better. you don't need 2 bar on your seals and gaskets if you can avoid it)

[Andy335Touring]

Never had a problem with mine, i'm using a face lift 325 expansion tank and cap, the rad was new when i did the swap in '04, it was bought from ECP