[Scorpion123]

Hi everybody, I'm new to the forum so be easy on me 😂.

I've recently developed a problem with my i30 1.6 Crdi that's driving me nuts: the car runs great but after use and when the engine is cooling down it seems to build up pressure in the cooling system after around 30 mins of of turning off the engine and blows coolant out the the radiator hoses even though they appear to have no leaks.

Just this morning I used the car and now it seems to be leaking from the water pump area after cooldown. I've tried replacing the reservoir cap and bleeding the system with no joy.

Has anybody got any ideas what might be causing this build of pressure issue? I'm starting to think possible head gasket or head crack maybe?

Thank you
regards
Peter

[BrendanP]

I would expect the header tank cap to include a pressure release valve that would relieve the pressure long before it got high enough to blow coolant out through the hoses. Does it look like coolant is being forced out where the hose goes over the spigots on the radiator? If there was a head gasket leak or cylinder heat crack I'd expect to see water getting into the oil (emulsified mayonnaise-like deposits on the oil filler cap) or an oily film in the coolant.

Just a thought, but could there be an airlock in the engine block? The coolant expands a bit when it gets hot, but not by much, whereas air expands a lot more when heated, causing the pressure to rise. Or there's a localised block where the coolant flow is restricted so it's turning to steam?

Do you keep having to top up the coolant?

[Scorpion123]

Thanks for your reply Brendan, yes my first
thought was that it might have been the reservoir cap so I ordered a new one from my local Hyundai dealer but the pressure issue still remains. I've bleed the system twice by running the engine up to temperature with the cap off and my heaters running full plus squeezing the hoses to push out any air. Before this problem I didn't seem to lose any coolant and there's now other signs of head gasket failure like oil in the water or vice versa. The pressure only builds up around 20 to 30 minutes after driving the car you can hear it the system hissing and the coolant leaks past the sprockets and yesterday it seems as if it's damaged the water pump now as there's a visible leak under the alternator area. Sorry to waffle on 🤣

[Greyhound]

and there's now other signs of head gasket failure

Is that a typo? Do you mean "no other signs of head gasket failure"

[Scorpion123]

Sorry Greyhound yes it was a typo mate. Theres no other signs of head gasket failure but it still could be.  I'm unsure if it's worth keeping putting money in to it as it's a 2009 plate. It's leaking from water pump area now which looks a pain to replace, I'm worried if I replace it it will burst again with the pressure in the system. I've ruled out the coolant cap and a airlock in the system I'm just not sure what else it could be

[BrendanP]

I've never changed a water pump, but it doesn't look too difficult. It's all accessible from the end of the engine, you might need to take the front right wheel off and the wheel arch liner to get to it. What seems odd it that the pressure builds up after letting the car stand. There's no longer any heat being produced other that what residual heat there is in the engine block, and once the coolant is no longer being pumped around that heat might cause expansion in unexpected air pockets. That's the only thing I can think of.

[Greyhound]

Bad water pump is one diagnosis of coolant leak when car not running here: Why Is Coolant Leaking From My Cars When It's Not Running?

You say you have replaced the coolant reservior cap. Does the radiator also have a pressure cap. If so, was that replaced?
Have you given cooling system a comprehensive flush to rid it of any sludge/debris before filling and bleeding.