Coolant issue

[Deadskittles]

Hey Forum, need your help with my 318i M10. I just finished my turbo/engine rebuild and install and i went to drive the car and whenever i get into the high rpms or hit boost i can see coolant splurge out of the coolant cap. Me and my friend came down to two conclusions.

1. Too much water in system and is expanding too much

2. Too much coolant? how close is it to the top of your radiators?

(Note: I did do a coolant bleed with the thermostat opening)

Do either of these make sense?

Thanks!

[jeffnhiscars]

I fill it close to the top and let the excess overflow after which it settles about 3/4-1 inch below the cap and stays there forever. I dont know what piping you may have added or changed but they usually self bleed as long as the heater valve is wide open.

If this continues past a brief overflow stage you may be getting exhaust pressure in your cooling system.

[Hey_You]

Possible bad radiator cap, that's a possibility. Or like jeff said, headgasket leak

[Deadskittles]

I would say the head gasket is quite unlikely since its brand new. Could the coolant line that runs to the throttle body be a possibility?

If it helps, during the buildup of pressure if i leave the cap on the two top hoses expand quite a bit, and after if i leave it sit with the cap on the collapse on themselves and expand back to normal when i open the rad cap.

[E30_Pare]

Doesn't matter if the head gasket is new if head was torque incorrectly. Anyways I'd start with what's easy & cheap first before getting cuhrazy

[jlevie]

That has to be a bad expansion tank cap or a leaking head gasket. And since you say it happens every time you hit the upper end of the rpm band the chances of it not being the head gasket are extremely low.

[Deadskittles]

Alrighty, Thanks for the input. Tomorrow im going to go down the list and see if i can figure this out. Ill let you guys know whats up.

[jeffnhiscars]

That has to be a bad expansion tank cap or a leaking head gasket. And since you say it happens every time you hit the upper end of the rpm band the chances of it not being the head gasket are extremely low.

There is no expansion tank on a stock M10.

If the hoses collapse on cool down the radiator cap vent hole is plugged preventing air from returning to the system as it cools.

Head gasket...again. Newly installed gaskets leak frequently. Did you deck the head ? What kind of gasket ? new head bolts ? etc etc

[Deadskittles]

Head was only decked to make sure it was perfectly flat. Headgasket is elring, Today im going to make sure that all bolts are torqued correctly.

[jeffnhiscars]

start with your radiator cap. I'm as sure as I can be online that the vent is plugged

[Hey_You]

I had an issue with coolant leaking after I did my headgasket/head rebuild. I was worried it was the headgasket and did a chemical block test. It wasn't my headgasket. Followed the trail and found my radiator cap gasket had a slight tear and would leak. Check there first, then run a block test, that's my recommendation.