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Matt, Engineer
Category: Car
Satisfied Customers: 21867
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Isuzu FTR: 07 Isuzu FTR keeps blowing heater hose? heater cores

Customer Question

07 Isuzu FTR keeps blowing heater hose? heater cores are new, new engine, new thermostats, new reservoir cap, new radiator, new heater hoses, new water pump...
Submitted: 4 years ago.
Category: Car
Expert:  Walt-Mod replied 4 years ago.

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Expert:  Matt replied 4 years ago.

if you haven't already then the thing to try is a head gasket / block test kit as these take a coolant sample and analyse it for any signs of combustion gas - if present this would indicate the head gasket is on its way out
Customer: replied 4 years ago.
The engine was just installed because the head gasket went out and the supply line to the heater core also blew, we upgraded the radiator to a four core from a 2 core. We also got rid of the stock trans cooler and installed a high flow trans cooler. On the second test drive the same heater line blew, which was also replaced at the same time. We then replaced the heater cores, it takes two. The reservoir cap was also replaced along with two new thermostats on the engine. The only thing that is left is the thermal valve going to the reservoir which is also plumbed to the turbo. What else could it be? Would there be a pressure or flow regulator at the water pump going to the heater cores?
Expert:  Matt replied 4 years ago.

the only regulation of water flow around the engine is done by the thermostats and the size of the water hoses

so it does sound to me that the system is still being overpressurised to me

as you've already replaced the head gasket its possible that there may be a crack in a cylinder head thats gassing up the system

so I'd still suggest doing a block test as the next step to hopefully eliminate this as a possibility
Customer: replied 4 years ago.

We tested for combustion gases using the block tester and we got a negative result. we also installed a pressure gauge on the reservoir and the max pressure we got was 3 psi, during a stall test I wouldnt think the cylinder is cracked since the whole engine is new, but anything is possible. Would an air pocket cause this, what is the purpose of the thermal valve on the system?

Expert:  Matt replied 4 years ago.

OK an air pocket would give this result so its well worth checking that all the small diameter hoses that run from the top of the radiator and top of the engine back to the header tank are free flowing and not blocked

the thermal valve is there to vent from the turbo once its all up to temperature so it only opens once the engine is fully warm and working hard
Customer: replied 4 years ago.

I think the air pocket is the only that is left if everything else has been replaced. The thermal valve is in-line with the top small radiator hose going to the reservoir and the turbo tee's off from that line after the valve. What effects would bypassing the thermal valve have if any?

Expert:  Matt replied 4 years ago.

Its worth a go as the valve should bleed through a small amount all the time and then open up with high temperature so yes if it was blocked then it could create an air pocket behind it

so yes try bypassing it as all it'll do is make the turbo run a bit colder and hurt the boost response / turbo lag