Coolant leak from behind thermostat/VANOS unit. Any ideas?

B

BigDaddy

Member
Hello guys been a while but I’ve been trying to get to the bottom of my coolant leak issues off and on for ages. Now replaced waterpump, expansion tank, radiator hoses, temperature sensor and thought I’d cracked it. However I went for a drive today and the coolant light came on yet again. When I pulled over there was a pretty bad leak from above the thermostat. Not the thermostat itself though, definitely above and behind it. Not easy to see but visible with the torch. Looks like it’s coming from the cylinder head area but I don’t know as I haven’t stripped it all down yet.

I know this is a bit vague but any ideas before I start the ballache of stripping the cooling system down yet again?

Cheers
 
BigDaddy said:
Here’s a poorly shot video of it.


https://youtube.com/shorts/klBRxjTfZ5o?si=DLQ4e14DINiOFXbw
Click to expand...
Is it just me?
Can't see the video....... says it's private?
 
Yup that works but you’re right it’s pretty vague.
I think personally I would want to be hands on to give you any guidance on that.
 
Yeah it is very vague, it’s hard to get the camera in there really, I’m going to strip it all down I just wondered if this is something common or not at all. I’m really hoping it will all become clearer once the pipes and whatnot are off.

I don’t think bmw like cooling systems. Mine has been such a pain in the arse, feel like I’m just constantly chasing problems round the engine.
 
Have you considered getting a pressure test done on it? You'll be able to see (hopefully) where the water is coming out from when it's cold (rather than it being steam/too hot to tell)
https://dsportmag.com/the-tech/how-to/quick-tech-cooling-system-pressure-check/
 
Thing is it’s a massive pain in the arse to even see where it’s coming from other than top of the engine because access is so tight. It is a good idea for testing once it’s done though, if I can do it. I do have a kit that Ive never used.

Starting to get a bit disenchanted with zed ownership if I’m honest. I just want a bit of time to enjoy it without constantly stressing about coolant issues.

Anyway will update once I get the tools out and whatnot in case it helps anyone else.
 
BigDaddy said:
Thing is it’s a massive pain in the arse to even see where it’s coming from other than top of the engine because access is so tight. It is a good idea for testing once it’s done though, if I can do it. I do have a kit that Ive never used.

Starting to get a bit disenchanted with zed ownership if I’m honest. I just want a bit of time to enjoy it without constantly stressing about coolant issues.

Anyway will update once I get the tools out and whatnot in case it helps anyone else.
Click to expand...
I can't think of anything else up that high?
Just check it's not the hose from the expansion tank. I had a seal give way in one at the engine end and it fired coolant across the top of the thermostat area.
 
Had a bit of a fiddle today. I think the waterpump has failed. Took it out for a run today and the radiator fan came on pretty much straightaway but the blowers were cold. The temp went up to the middle on the dashboard but that was it, no heat from blowers. When I checked the expansion tank it was empty but even when I refilled it there was no water coming from the return when I ran the engine with the cap off. I think it may have failed and sprayed water everywhere. I don’t know really. Either way I’ll fit a new waterpump and try again. I believe that’s a bit of a pain in the arse but I have to have a go at it. It definitely looked like the water was coming from way higher than the pump location. I have a bit of a worry that the head gasket has failed badly and the water was leaking from the head but I don’t really know. Maybe the pump has failed and the head gasket too.

Anyway time for lots more swearing and more money simply trying to get the car to run like a normal car.
 
After a bit of thought I tested the waterpump again and it is actually working. Have now bought a coolant pressure testing kit, I thought I had one tucked away but I didn’t. Anyway fingers crossed this will show me where the leak is coming from.

The Zed will ride again!
 
I’ve not been able to look at this for a while as I’ve been busy but I finally hooked up the coolant pressure testing kit I bought and it looks like the coolant is coming from the engine itself, behind the thermostat and to the left of it as you look from the front. It’s basically where the vanos unit is. I know there shouldn’t be coolant coming out of there but for some reason there is.

Check out my poorly shot video (hopefully a bit better quality than before).

https://youtu.be/iQtnBdrVjnI?si=jR1elGlCenwHdjBt
 
Anyone with any ideas? It is a strange leak. I’m wondering whether somehow coolant is finding its way in to the vanos unit and when the pressure is high enough forcing out, I have no idea how that would be happening though.
 
There is no coolant in/around the vanos

I’d say your video shows that the thermostat housing is leaking or hasn’t sealed properly against the face?

How much fluid are you losing? Is it p155ing out or just a dribble?
 
The thermostat housing should come with the seal already installed. However I bought one from a reputable seller and a good brand and just before i bolted it together I noticed there was no seal fitted!
Could it be the same has happened to you?
 
The thermostat was a bmw part and did come with the gasket.

The coolant is coming from the metal, to the left and slightly above the thermostat housing where the two parts join, not from the thermostat housing itself. It’s not easy to shoot on video as there’s not a lot of room in there but it dribbles down onto the housing but it’s not coming from there. Easier to see in the flesh than on video.

I'll pressurise it again in the morning and take a video of the leak starting so it is more clear.

Thanks for responses though. I would love to get to the bottom of it as this is the last coolant leak so if I can sort it I’ll be buzzing.
 
I guess you could have a crack in the head… like I’ve never seen it but that doesn’t mean it couldn’t happen?
 
I’ll double check it tomorrow. I’m hoping that you’re right and I got it wrong. Fingers crossed that’s the case.
 
Thanks for the help chaps. I used the pressure kit again but this time filmed it as I pumped the kit. You can see the fluid start to come out of the thermostat where it meets the head. I think what must’ve been happening before was that the pressure blowing air out as well as coolant must’ve forced it upwards and away so it looked like it was coming out of a completely different area.

I torqued the bolts up to 10nm before, which apparently is the correct setting, however this time I just nipped them all up a bit more until the leak stopped. I guess slavishly following torque settings is not always the best idea.

I’ve just pumped it up to 1 bar and after a cuppa will go and check that it’s still holding pressure in a bit. Leak appears to have stopped for now though.

Thanks for the comments, I for some daft reason was sure that it was a crack in the head as it looked exactly like that when it was fully pressurised. Going slow and steady with the kit is definitely the way to identify these things.

https://youtu.be/jXvHp47lCHo?si=3Xa-NizrPe-hbwDp
 
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