This will toggle some brains

[payney8]

Hi, girlfriends car wont start. She got it hot and kept driving it till it died. I went and picked it up towed it home. Let it cool over night. Now with a good battery in it in cranks but wont start. It wont hold much coolant as there is a split in the thermo housing somewere. Any ideas? it is a 1989 318i. :wgaf:

[87e30]

Check your oil... probably blew a headgasket at first and then did more damage if it now won't start. I'll bet there is coolant in your oil.

[payney8]

Nope no coolant in oil. Oil smells burnt as hell though and inspection of the upper end shows lots of burnt oil. So its been very hot. engine cranks and still has alright compression.

[Mossman]

it sounds like it has alright compression or you compression checked it?

[payney8]

Compression checked it about 105 all around

[payney8]

any thoughts?

[Kerrath]

105?... Shouldn't it be more like >160?
Seems way off.

[nando]

105?... Shouldn't it be more like >160?
Seems way off.

it's not the absolute # that is important, it's the difference between cylinders. the absolute # doesn't mean anything because how it's tested can vary from engine to engine and person to person.

if they were all 105 his compression is fine. if one cylinder was 80 and the rest were 105, then he'd have something to worry about.

[Farbin Kaiber]

Sounds mind boggling.

[calz4m]

My bet is the headgasket is blown. Remove the plugs and check them. You can also crank the motor when the plugs are out and look for coolant. Don't be leaning over the motor when someone does this as coolant could shoot out of the spark plug hole(s). Trust me, its happend to me once before. Luckily car was cold, as yours will be. Can you elaborate on the circumstances surrounding the initial overheat? Perhaps with all the information we can make a more educated diagnosis. Did it dump all of its coolant? Did the oil pressure light come on?

[Kerrath]

it's not the absolute # that is important, it's the difference between cylinders. the absolute # doesn't mean anything because how it's tested can vary from engine to engine and person to person.

if they were all 105 his compression is fine. if one cylinder was 80 and the rest were 105, then he'd have something to worry about.

When they're supposed to be like 160+ and he's netting 105, there's gotta be bad rings or valve seals involved or something.

[nando]

When they're supposed to be like 160+ and he's netting 105, there's gotta be bad rings or valve seals involved or something.

but you don't know they are supposed to be 160+. maybe he didn't crank it long enough, maybe the engine was cold, maybe he didn't hold the throttle open.

[SpecM]

and the engine would still start and run, even with low but even compression

not well, but it would start

OP: its an m40 I assume? (you live in Oz, so you get euro engines, yes?)

[Fast Frankie]

you mentioned "now with a good battery". Do you mean to say the battery went out at the same time as the overheat? Why was the battery replaced?

[Kerrath]

but you don't know they are supposed to be 160+. maybe he didn't crank it long enough, maybe the engine was cold, maybe he didn't hold the throttle open.

I asked the internet, it told me M42s are specified as 160+. Additionally, every thread of compression test results I found shows the PSI as being between 155-220. Nothing anywhere near that low.

Maybe he didn't crank it long enough, maybe it was cold, sure, but if that screws up the pressure as much as it did, then it definitely doesn't make for an accurate diagnosis of compression variances.