High pressure in cooling system

Letsgodisco · Nov 16, 2009

Hi all,
I haven't posted on here for ages as my old disco has been really well behaved. However I now have a 1998 300 TDI thats being a pig!
The coolant was like drinking chocolate so I've flushed out the system and added antifreeze and water 50/50. The thermostat had no centre in it, so I've fitted a new one. New brass plugs have been fitted to the rad and stat housing previously.
Iv'e tried bleeding the system in various ways but the metal pipe along the top of the head doesn't get very hot. The heater gets hot briefly then goes cold. All the hoses seem to get very hard after a short time running the engine.
The head looks quite new but I'm tempted to remove it as I fear the head or the gasket is knackered.
Before I attack it, am I missing anything obvious:doh:.
The engine starts and runs fine - no water in oil or vice versa.
Thanks
Paul.

eddyoz · Nov 16, 2009

Try bleeding the system again and use a known good cap/or new, on the coolant reservoir?

Letsgodisco · Nov 16, 2009

Thanks for the reply.
I've bled it about 5 times over the weekend trying different methods but still get the high pressure (hard hoses). The cap appears to be quite new, but I have another I can try.
Wouldn't a faulty cap cause no pressure rather than high pressure?

Dent · Nov 16, 2009

The coolant looking like "drinking chocolate" is probably an addative like k seal or similar, that together with the stat, looks like there's been a problem with it, sounds like new head gasket time.

Letsgodisco · Nov 16, 2009

Thanks Dent.
I just want to be certain I've tried everything before I remove the head (never done a OHV before!). I think the coolant was just very rusty water, couldn't see any coppery bits like K seal. When I cleaned the header tank the stuff that came out was almost orange.
I may go "all the way" and fit a new head, unless I can find a known good second hand one.

oldzed · Nov 16, 2009

Does the heater get hot and stay hot and is there any smoke (whiteish) from the exhaust. You may just have an airlock in the heater which could also be blocked by rubbish in the mattrix, perhaps some flushing agent would clear that. You can get the system pressuried which would confirm if the HG was leaking and some garages use a HG sniffer. I think they stick it into the radiator water and it can detect combustian gases. I would get one of these carried out first unless you like getting intimate with yer toolbox. Ooo er.

PASTMASTER · Nov 16, 2009

Letsgodisco said:
I may go "all the way" and fit a new head, unless I can find a known good second hand one.

Can't see any reason for fitting a new head without testing the old one. An engine specialist should be able to pressure test and skim it for you. You'd need to get that done to a second-hand head anyway unless you were certain of its history.
Your problem may be down to gunge in the cooling system rather than the head.
In my experience, a cracked head always ends up giving you steam in the exhaust sooner or later.

Letsgodisco · Nov 16, 2009

oldzed said:
Does the heater get hot and stay hot and is there any smoke (whiteish) from the exhaust. You may just have an airlock in the heater which could also be blocked by rubbish in the mattrix, perhaps some flushing agent would clear that. You can get the system pressuried which would confirm if the HG was leaking and some garages use a HG sniffer. I think they stick it into the radiator water and it can detect combustian gases. I would get one of these carried out first unless you like getting intimate with yer toolbox. Ooo er.

The heater gets hot then goes cold. The exhaust seems fine. The pressure test sounds a good idea.
The new coolant is getting darker, I think there may be tiny soot particles in it

or i'm getting paranoid!
Thanks for the suggestions.

Letsgodisco · Nov 16, 2009

PASTMASTER said:
Can't see any reason for fitting a new head without testing the old one. An engine specialist should be able to pressure test and skim it for you. You'd need to get that done to a second-hand head anyway unless you were certain of its history.
Your problem may be down to gunge in the cooling system rather than the head.
In my experience, a cracked head always ends up giving you steam in the exhaust sooner or later.

Thanks Pastmaster.
I'm out of touch with prices for testing and skimming and not sure of the amount of stripping needed.
Looking at fleebay, I've seen a scondhand head, pressure tested and skimmed at £150 or new head at £275 exchange.
The second hand one seems a good bet to me for a speedy repair but again i'm not sure if it's a good price.
Any comments very welcome.

High pressure in cooling system

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