Any Tips For Locating Coolant Leak?

Retrogamer

I've had a very minor coolant leak on my 1.9TDi (PD130 for 2 and a half years now.
It's been pretty minor during all this time and usually would take around 1000 miles / 1 month for the level to go from max to minimum. About 1/4 litre or so at a guess.

I had a quick look, checked all the pipes previously and as i couldn't find anything obvious i put it down to a trivial issue and just continued to top up and ignore it.

During all this time, when ever i unscrew the header tank cap it hisses. This happens when it's both hot and cold.

I'm a bit rusty with this stuff but from memory if the header tank is pressurised and hissing when the engine is cold, it would usually indicate exhaust gasses getting into it? Is that right, or could something else be causing the hissing?

I've covered approx 27k miles since i've owned it and it's always been this way so thought if it was head gasket failure, then it would have failed before then.

arcon5

No it means the cooling system is pressuring as its supposed to. You can see HG failure in the return pipe - usually bubbles loads if severe.

George_Michael

Retrogamer wrote: »

During all this time, when ever i unscrew the header tank cap it hisses. This happens when it's both hot and cold.

I'm a bit rusty with this stuff but from memory if the header tank is pressurised and hissing when the engine is cold, it would usually indicate exhaust gasses getting into it? Is that right, or could something else be causing the hissing?

It's possible that something as simple as a faulty radiator cap could be causing this.
If the pressure valve in the cap is opening too early it would be letting hot coolant into the tank (which would pressurise the tank slightly) and if the pressure valve wasn't allowing the fluid to return back to the radiator when required, it would stay pressurised even when the engine had cooled.

Marktheshark

When it goes for MOT ask the tester to sniff test the header tank, if the HG is leaking the HC reading will jump to 999ppm

scotsbob

I would agree with the poster above and consider the cap first of all. The cost of replacement is minimal. replacing it will either solve the problem or rule it out as the cause.

reeac

I once had the same symptoms (or rather my car did) I.e. Remained pressurised after cooling down and it turned out to be the head gasket. It would remain pressurised for a week or more.

jimjames

I had a similar leak in my 1.9 TDI, there was a small split in a hose that wasn't easily visible initially but when it warmed up the hose opened more and leaked more heavily making it easier to find. This car had done over 240,000 miles so the hoses were getting a little perished. This video shows the location


https://www.youtube.com/watch?v=DlEFvZ6gJoo

Retrogamer

George_Michael wrote: »

It's possible that something as simple as a faulty radiator cap could be causing this.
If the pressure valve in the cap is opening too early it would be letting hot coolant into the tank (which would pressurise the tank slightly) and if the pressure valve wasn't allowing the fluid to return back to the radiator when required, it would stay pressurised even when the engine had cooled.

Thanks, i'll get another cap for it and see how that goes.

Marktheshark wrote: »

When it goes for MOT ask the tester to sniff test the header tank, if the HG is leaking the HC reading will jump to 999ppm

That would be problem for me as the MOT is in about 10 months time and i'm looking to sell it shortly but would rather fix this issue than pass it onto someone else.
The header tank was replaced shortly after i got the car when i thought i had fixed the leak. I done a full coolant change at the time and wanted a clean header tank. It's still really clean so hoping that's a sign there's no exhaust gasses getting in.

tberry6686

have a look at all the coolant hoses. If it is leaking when it is hot then you will get some dried residue near where the leak is (and around the water pump, thermostat as well).

bigjl

Another vote for doing a sniff test.

It could easily be just leaking slightly wen hot from a hose joint due to a weak hose lip.

You can buy the sniff test kit online. They are not hugely expensive.

Mankysteve

You can get uv dye to add the coolant and track with a uv lamp