Spilling coolant from pressure tank cap
 

Hello everyone

Yesterday I was in the motorway and after a quick stop, I noticed some steam coming out from the engine bay. When I opened I saw this:

https://farm5.staticflickr.com/4844/...a4001d06_z.jpg

https://farm8.staticflickr.com/7924/...edbd8510_z.jpg
After inspecting the area it seems the problem was coolant being spilled from pressure tank cap.

Some facts:

• My radiator fan is fully working
• Just some moments before I overtook a car and I rev it up a bit to a range of +/- 5000rpm
• I did not overfill the coolant beyond the "MAX" mark in the coolant reservoir.
• After this incident, the coolant level naturally decreased but not too much. I could still see coolant in the reservoir but it was below "MIN". I was afraid to open the cap with the engine hot.
• Right after checking this, and while entering back to the motorway I feel a clear loss of power until I foot down the accelerator and suddenly everything got back to normal.
• I used the IKE diagnostic to check the temperature of the engine and it appears normal ( between 90 and 95ºC)
• The entire trip (224 Miles) the car did not lose more coolant.

My questions:

My first suspect is the pressure tank cap. There is any common fault known with them?
Could this situation also indicate a problem with the thermostat housing?

Any comment/help would be very appreciated

Thats what mine did. I got a new coolant cap from DMGRS and all was well.

The seals go on them.

Also make sure you do not have to much coolant in the header tank, only fill to the max mark photo below.

If you can not get a new cap add new coolant rings using Viton ones.

I'd be wary of Ebay ones. I got one and it leaked worse than the one it was replacing!

It's only the o-rings, and they're supplied by a forum member on here. Safe as houses!

That's what I get for just glancing at the ad, didn't notice it was Viton O rings and not the cap.

Thank you very much for all your answers. I was quite concerned about this.


Previously in my 400 Series I had a similar problem and it was a faulty coolant cap valve. I replaced the cap and was the end of the problem.

I have exactly the same problem as Copilot (post 1) and fitting a new tank cap did not solve it.

If the coolant level is on the MAX mark (measured at cold) it leaks heavily from the tank cap as soon as the engine warms up.

If the coolant level is roughly 500ml below the MIN mark (measured at cold) it doesn't leak at all from the cap.

I have no idea what the cause is. :shrug:

Hi Pedro
Have managed to solve the problem now? or is it still leaking from the cap.