P38 diesel mystery coolant loss

Hi all, I tried a search but couldn't find anything, the coolant level seems to be dropping a little over a few days, the system has been pressure and sniff tested which revealed a dodgy cap which I've replaced. There isn't any visible leaks so I a little lost, any help appreciated.

Have you checked the oil to make sure it isnt going into engine??

I would look in the footwells of car, sounds like you o-rings maybe leaking if you cant find anything under the bonnet...

Also check how well your return line from radiator to top up bottle is sealed on the rad. As mine used to breathe some until i replaced the hose clamp.

Hi, sorry forgot to mention I've done the o rings, the oil doesn't seem creamy at all, also when I've taken the cap off and revved the engine to try and bleed any air the coolant level did drop, if there is a leak somewhere can the coolant just evaporate away? Cheers gaz.

Gazza36 said:

Hi, sorry forgot to mention I've done the o rings, the oil doesn't seem creamy at all, also when I've taken the cap off and revved the engine to try and bleed any air the coolant level did drop, if there is a leak somewhere can the coolant just evaporate away? Cheers gaz.

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Get it static tested that will tell you if there is a leak.

Pardon my ignorance but what's static testing? Thanks.

Small leak at the throttle body maybe?

odysseus said:

Small leak at the throttle body maybe?

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On a diesel?
Split in expansion tank underside is a possibility.

Datatek said:

On a diesel?
Split in expansion tank underside is a possibility.

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Yeah that confused me as well for a minute, I'll have a look, when I squeeze the two big radiator hoses bubbles appear in the expansion tank so maybe an air lock but surely it will eventually all come out. Thx

Gazza36 said:

Pardon my ignorance but what's static testing? Thanks.

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Static test is a tool applied to header tank in place of cap. System can then be pressurised and checked for pressure drop and therefore a leak. It can also be used with engine running to check for pressure build up.

Gazza36, where abouts in Cornwall are you?

Davlyn said:

Gazza36, where abouts in Cornwall are you?

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Hi, I'm normally just outside Newquay but I'm in Sussex until Thursday, the car has been pressure tested I that's the same thing?

A new development, after the car had been running there was coolant on the bodywork underneath the breather pipe that comes out of the expansion tank next to the cap.

Gazza36 said:

A new development, after the car had been running there was coolant on the bodywork underneath the breather pipe that comes out of the expansion tank next to the cap.

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If it's comming out of the overflow you have a bad new cap or its over pressurising .

Grit Valve said:

If it's comming out of the overflow you have a bad new cap or its over pressurising .

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Or he has put to much in an it's the excess being expelled.

wammers said:

Or he has put to much in an it's the excess being expelled.

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I only fill it to the cold line, what could cause overpresurrising if not the head gasket? Cheers.

Gazza36 said:

I only fill it to the cold line, what could cause overpresurrising if not the head gasket? Cheers.

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Airlock, but if the bleed pipe is clear as you refill system, and it's done properly it's really hard to have an airlock on these engines. Try running engine from cold with cap off and burping hoses. Make sure the bleed pipe is clear of coolant first. Is the new cap you fitted a proper one or a chinky copy? I suggest you get it static tested again and check how much pressure is built up when engine is hot.

wammers said:

Airlock, but if the bleed pipe is clear as you refill system, and it's done properly it's really hard to have an airlock on these engines. Try running engine from cold with cap off and burping hoses. Make sure the bleed pipe is clear of coolant first.

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I would defently agree make sure that bleed hose is clear I blew mine out the pipe is clear but the expansion tank bleed hole feels restricted .

What I do now is remove the bleed hose from radiator end get a clear hose on the end with a funnel attached pour some coolent InThe pipe with the bonnet open wedge the pipe up high in the bonnet catch spring and watch the bubbles come out . When the car reaches temputre turn off connect original bleed hose allow to completely cool then you should find you need to top up expansion tank again once air has expelled itself

The cap is bearmach, is there any way to make sure the bleed hose is clear without compressed air as I don't have access to any, ie could I just take it out and drain it or blow through it? Cheers.

Gazza36 said:

The cap is bearmach, is there any way to make sure the bleed hose is clear without compressed air as I don't have access to any, ie could I just take it out and drain it or blow through it? Cheers.

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Yeah take it off the rad (carefully) put it to your lips and blow through it. Cap is a chink copy then or was it described as OEM? Proper caps should vent above 15 psi and fail completely at 22 psi to prevent system damage. If the cap is venting early that could be your problem. It is possible to pressure test caps, if it blows off at anything less than 15 psi it is no good.

what about the metal pipe running around the back of the engine they have a habit of rotting and leaking