Thread: Bleeding Td5!

OK so is it pressurising the system or are you having trouble bleeding air from the system?
If it is a bleeding problem patience is required, however...

Sorry but im going to say it anyway... if it is pressurising the system you have a crook head gasket.
The coolant system (head gasket) may hold back 20- 60-100 psi but the test cannot replicate a the leak past of a few hundred PSI forcing past the fire rings into the system. That's the difficulty of detecting small Head Gasket faults on Diesels and particularly the TD5 head movement.

I get your point but surely they should be able to detect exhaust gases in the system?

The way I understand it air in the system allows the coolant to boil thereby introducing excess pressure...... ?

I agree, I haven't had any success with exhaust has analysis in any diesel with small gasket problems.
Both the TD5 in our family had the check and both passed.
The system relieves via the cap at approximate 22psi If I recall.
You have around 14psi normally from heat expansion. For example now you only need .1 psi blow past from 1 cyl for 10 minutes and you're blowing past the cap.
Usually folks do the hoses and cap then discover the water pump is leaking too as the pump seals are old and now the next weakest link.
If you get the right circumstances ( long high speed trip)
You push enough coolant out to overheat.
While running around short trips often don't reveal more than a slight coolant drop.

head gasket or walking head.

search and do the coke bottle bleed.

if you cant top it from filling the coke bottle with air while spilling out the coolant its the head, gasket or a holed bore

Have you done a leak down test

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Thanks for the replies.

Further info - it has had a new head previously so no plastic dowels to worry about. It was running fine with no air in the system until the thermostat was replaced, that's when the trouble started!

Just a couple of questions when you say pressurizing the cooling system have you tested it with a cooling system pressure tester or it just spitting coolant out the cap?
If just spitting out the cap have you tried a new cap sometimes its the simple answers

Are you running proper coolant as in not just straight water im asuuming coolant but if a weak mix of coolant or straight water it will boil.

Egr still connected? Could possibly be letting air locks in through the egr cooler as they can crack internally causing similar symptoms to a head gasket, easily checked by pressurizing the cooling system and looking inside exhaust passage for coolant.

There still is a possibility that the head has a small crack as mentioned CO2 test doesn't always show as a fault with small diesels with a small crack or gasket leak and could have been caused by an air lock after changing the thermostat. Best way is to make sure it definitly blead then do pressure testing, leave tester on while running engine and watch for rises then shut down and look for a pressure drop and check for leaks. if you're loosing coolant and it not externally it will be inside the engine some where either cylinder or egr cooler

Check that the new thermostat is fitted correctly.
It is possible to have the main and bypass hoses on the wrong way round.

I have seen it before.

Paul.