How reliable are block tester for head gasket failure?

[Steviesam]

Wife's Peugeot had a small water leak. Today it got much worse and we had to stop 4 times on a 30 minute journey to top up the coolant.

Could see some steam when we opened the bonnet, but couldn't see where from.

Used a block tester thing, and the fluid very quickly turned yellow from blue.

Can I assume its the head gasket?

Thanks

Edited by Steviesam on Friday 6th June 21:48

[GreenV8S]

The block tester tells you there are hydrocarbons in the cooling system. HGF is the most obvious potential source, but it could also come from anywhere else where the cooling system is exposed to hydrocarbons, such as an EGR cooler. More serious problems such as a cracked block or leaking cylinder liner could show up in the block test too. No idea what other possible sources there may be on your car.

A leakdown test could be used to confirm that it's HGF or block failure, if it shows leakage from the cylinder to the cooling system. If so, the next step would be to remove the head to investigate either way.

Are you doing this diagnosis and repair yourself? If not, this is really for the mechanic doing the work to figure out, not you. If you start 'back-seat driving' the diagnosis and repair then you could potentially waste time and money for the mechanic to do unnecessary work at your direction.

[E-bmw]

Steviesam said:

Wife's Peugeot had a small water leak. Today it got much worse and we had to stop 4 times on a 30 minute journey to top up the coolant.

Could see some steam when we opened the bonnet, but couldn't see where from.

Used a block tester thing, and the fluid very quickly turned yellow from blue.

Can I assume its the head gasket?

Thanks

Edited by Steviesam on Friday 6th June 21:48

I assume you mean turned blue to yellow.

Only ever seen the stuff that starts blue.

They are 100% accurate, it is a chemical reaction th the hydrocarbons.

[Steviesam]

Thanks guys.
To be honest, I am going to throw the car away if it is the head gasket. It’s just not worth it!

[paul_c123]

Steviesam said:

Thanks guys.
To be honest, I am going to throw the car away if it is the head gasket. It s just not worth it!

What car is it and where are you located?

[Steviesam]

Peugeot 3008 1.6 hdi, located in France!

[E-bmw]

Steviesam said:

Peugeot 3008 1.6 hdi, located in France!

If that is the one using the shared engine between Ford/Volvo/Mazda/PSA cars then I had exactly that with mine in a 2015 V40 Volvo. Replacement (significantly lower mileage) engine sorted it.

It wasn't too bad a job to do on the driveway with a hired crane.

5 days to remove/new cambelt/clutch/injectors and a few other bits all done together working 4 - 6 hours a day.

[Steviesam]

E-bmw said:

If that is the one using the shared engine between Ford/Volvo/Mazda/PSA cars then I had exactly that with mine in a 2015 V40 Volvo. Replacement (significantly lower mileage) engine sorted it.

It wasn't too bad a job to do on the driveway with a hired crane.

5 days to remove/new cambelt/clutch/injectors and a few other bits all done together working 4 - 6 hours a day.

I think it is shared with those cars yes. I just cant motivate myself to do that work myself. I dont think the car is worth it, its done a few miles and I never liked the autobox anyway. Thanks

[E-bmw]

Steviesam said:

E-bmw said:

If that is the one using the shared engine between Ford/Volvo/Mazda/PSA cars then I had exactly that with mine in a 2015 V40 Volvo. Replacement (significantly lower mileage) engine sorted it.

It wasn't too bad a job to do on the driveway with a hired crane.

5 days to remove/new cambelt/clutch/injectors and a few other bits all done together working 4 - 6 hours a day.

I think it is shared with those cars yes. I just cant motivate myself to do that work myself. I dont think the car is worth it, its done a few miles and I never liked the autobox anyway. Thanks

When I shopped around locally to me I was getting quotes of around £2.5 to 3.5k to swap the engine at local garages.

[Steviesam]

Been doing some investigating today and there is no water leaking from the egr cooler (which sits on the back of the engine (DV6).
But there is quite a bit of water running down the front of the engine, where there are no water pipes at all.
Seems to start half way down the engine, just where the cylinder head and block meet. Re did the sniff test and blue went to yellow in about 10 seconds.

[GreenV8S]

Steviesam said:

Seems to start half way down the engine, just where the cylinder head and block meet.

That seems like pretty strong evidence for HGF. You'd need to take the head off to confirm it.

[E-bmw]

GreenV8S said:

Steviesam said:

Seems to start half way down the engine, just where the cylinder head and block meet.

That seems like pretty strong evidence for HGF. You'd need to take the head off to confirm it.

^^^^ Wot 'e said.

Seems like confirmation to me also.

[SystemOfAFrown]

GreenV8S said:

A leakdown test could be used to confirm that it's HGF or block failure, if it shows leakage from the cylinder to the cooling system. If so, the next step would be to remove the head to investigate either way.

A leak down test checks for cylinder sealing issues, typically due to problems with piston rings or valves. You would need a pretty catastrophic breech of the head gasket to show up in a leak down testing as the cylinder pressure for testing is well below combustion pressure. More useful is to pressurise the cooling system and then inspect the head/block interface within the cylinder using a bore scope for any signs of coolant ingress.

[GreenV8S]

SystemOfAFrown said:

You would need a pretty catastrophic breech of the head gasket to show up in a leak down testing as the cylinder pressure for testing is well below combustion pressure.

YMMV, but in my experience when there's HGF into the cooling system you can trace the leak because the leakdown test puts air into the cooling system. The leakdown test results are less clear when there's HGF into the rest of the engine because the symptoms can get masked by the normal blow-by flow. Granted there may be cases where HGF only occurs under combustion heat and pressure, but there are plenty of cases where it doesn't.