325i Head cracking

[Speedtouch]

Does anyone know what actually causes the often-heard phenomenon of the 325i cylinder head cracking problem? In the Feb 2006 issue of Practical Classics magazine, they reckon it's due to heat soak and can be avoided by fitting a six-branch manifold. Is this true? Also would other precautions be worthwhile such as leaving the engine to idle for some time before switching off (like you're supposed to with turbo cars), using distilled water (with anti-freeze) in the cooling system to prevent corrosion, etc.

Also, which is the part of the head that usually fails?

Prevention is better than cure - anyone got any good tips?!

TIA,

[Ziggy]

Regular coolant changes with decent (I use BMW) coolant. & then touch lots of wood. & buy a spare.

I like the idea that my 6-branch helps reliability too though!

[Brianmoooore]

In the Feb 2006 issue of Practical Classics magazine, they reckon it's due to heat soak and can be avoided by fitting a six-branch manifold. .

Also, which is the part of the head that usually fails?

,

Interesting theory, and one I've not heard before!
Most of the cracked heads I've come across have gone in one or other of the rear two camshaft journals. This gives the common symptoms of oil in the water and water in the oil as the relative pressures of oil in the journal and coolant in the water jocket vary relative to each other.
Have also seen cracks in the exhaust ports and on the head face near the ports.

[Bobbydoughnut]

Not heard that one before either but must say that heat soak does make sense as a 6 branch stainless manifold would be better at heat transfer away from the head as against the cast manifold. As alloy is very susceptable to heat variations across its surface, which is why they are prone to warping, then the excessive heat at the exhaust side compared to the inlet side could cause enough of a variation across the head, so could warp under extremes and overheats or crack at the mating surfaces, again due to variations of heat between the surfaces.

In my experience though most of the major cracks occur under the journals as Brian mentioned as that is a known weak spot when heat gets excessive usually after an overheat and that is in the main where I have seen them cracking. In fact the M20 I replaced recently had a weld running a third of the way along the side of the journal posts. The regular, Recommended corrosion inhibited coolant is also critical for long life in a bi metal engine like the M20 as Ziggy has said.

[MikeeMiracle]

Wow, not heard this one for a while but I used to hear this regularly years ago when there was more E30's around. I believe the problems started when they changed to using soft alloy/alluminium heads.

[Martinaston]

Fitting an electric water pump to run for a couple of minuets once the engine has been turned off is a lot cheaper than a six branch, although still not cheap at over £100 for a new one.

[--alpina--]

Yeah its true bmw 325 heads do crack ive actually had one few years back as i had steam in the mornings then would be ok, then the oil and water would imulsificate so i whipped it off and done a compression test and found out under the cam shaft was a 2 inch crack, you could see it.. but when the test was done then it was like aaaaaaaaaaaaaaaaaaaarrrrrrrr there you are, i could have welded it but at the back of your mind it might go again, so i got hold of another one and compression test it which was fine, then i thought now its of, its gas flow and porting time... all well and was happy and sweet with performance, ssoooo yessss there prone to cracking.... i think on the earlier models were weak, later would be ok...


Regards

Jimi

[MikeeMiracle]

i think on the earlier models were weak, later would be ok...

Im pretty sure it's the other way around.

[garyp_E30_325i]

Cracking is due to not getting the heat out, so anything you can do to improve thermal transfer is good. Of course that's why the car has coolant and I've noticed on almost every E30/M20 I've looked at (not that many if I'm being honest) they all seem to have 'dirty' coolant systems - I've flushed mine about 4 times in 18 months, each time it gets better but not perfect yet... I'm beginning to think I may need to replace the radiator, think!?

Anyway, most important (as already said) is to keep your coolant clean, topped up properly with good quality coolant & water.

As for manifolds and 'heat sinking', well it's possible but if the engine is looked after properly and doesn't get into an overheat situation then it sounds like a long shot... but another reason to fit a 6-branch, if you need another reason

[Speedtouch]

Interesting answers from you guys - enlightening.

I agree with garyp_E30_325i about 'dirty' coolant systems. My'88 325iSE seems to have a permanent film of dark (possibly oily - though it's difficult to tell!) muck floating on top of the coolant in the reservoir, despite having had a recent cambelt change and replenishing of the coolant, though admittedly my car's radiator also looks like it's seen better days...

Anyway, the car just passed 125K miles today and runs very sweetly, so touch wood...

I like the idea of getting hold of a spare head or two. Do they take long to actually change?

Cheers!

[Speedtouch]

Cool, so not too bad then if the worst occurs. Alas, the scrappys around here are these annoying modern 'managed' ones, where you can't actually go in and have a good old rummage - boy do I miss that happy pastime Shall keep my eyes peeled for a spare head anyway...