300tdi overheating-this will baffle ya!

Hi guys ...throw your head around this one for me.

Over heating

• oil not contaminated
• water not contaminated
• replaced stat ...no change
• new rad fitted no change (£130 thank you very much!)
• no heater (more in a moment about that)
• no hose blockages (all been blown through)
• small hoses between header and them/rad are clear

...now if i fill and run to clear air lock all seams ok, when the cap goes back on she blows within a mile. If the cap is left off, she will run happily provided I don't go over 55mph. If i fill the system, leave the cap off she runs leaving 3rd of the rad with water but no heater. However ...as i come off the motorway (55mph) ..and just as the temp is rising ...there is a noise (sounds mechanical) from under the dash ...the heater then comes on briefly, the temp falls and the cycle is repeated! If i remove the hoses to the heater matrix and blow it appears clear ...coz water and air come out.

This has got me baffled ...I cannot sus this one!

question: what is the no noise that signifies the heater is about to come on? and where is the cold advance for the idle coz this is now activating (no been aware of it before!) ..and how do I cure the problem of the over heating?

Birty1

Have come across something similar to this in the past on older VW diesels and eventually the head gasket went - so I would be thinking that the hg could be on the way out .
Could be way off the mark - let us know when/if you sort it out.

Sounds like head gasket failed letting combustion gasses into your coolant this gives the head a hot spot super heats yer water, causes rad cap to blow due to pressure when reved, and air lock yer heater matrix with gasses, youle also find it gets very hot very quick, get a garage to do a test, from what i remember from mine doin it they put a chamber on yer rad cap and they can tell if combustion gasses are in yer coolant if they are its head gasket or a crack somwhere... hope this helps cartman690...

I think theres a bottle of magic jollop by wynnes or someone you can add to your coolant to solve this, try halfords or a good carparts shop worth a try even if its just a temp repair good luck feller...

You know I hate to admit it but I think the heads gotta come off ....d*m ba*t*rd tw*ting thing!! (excuse the french)

Why does this happen when you're busy, and can't be with out the car?

Birty1

Before you take the head off,just have a look at the water pump impeller,make sure the thing is circulating the coolant.

I've ran the engine with the heater matrix pipes disconnected and the pipes off to check the pump and water poured out, I also checked it with the rad filler cap off and I could see the flow. The pump was my first though although new 18 months ago.

Birty1

almost certainly the HG or a cyl head problem. seen a few like it before on various cars.
you dont always get cross contamination with HG problems.

Yea, get a garage to "sniff the water" with the sniffer test.

might be worth givin this stuff a try...http://www.barsproducts.com/product.cfm?id=41 it works by sealing the leak when the gases hit yer coolant i know a buddy who tried it and it worked...good luck matey...

take the rad cap orf and look in the filler while th eengine is running.; if its yer head you should see little bubbles of grey gas coming up.

Get your head gasket done NOW!!!!!
This is exactly what happened to mine, it cost me nearly 2 grand for a new engine.