12HT cooling problems.

[12HTHJ75]

I own a HJ75 Series landcruiser. I have replaced the original 2H engine with a 12HT which has given me no trouble for 3 years until recently. During normal hwy driving the radiator spat 1/2 of its coolant out the overflow. After refilling bubbles can be seen in radiator at idle and frothy bubbles at 2000rpm. After getting looked at by a Toyota mechanic no HC were found in the cooling system. After replacing the thermostat and radiator cap the problem persisted.
No evidence of water in oil at oil change.
If its not the head gasket could the turbo be pushing air into the system through its cooling jacket?
Any ideas would help.

 

[Radd Cruisers]

I would suspect a bad radiator or a headgasket.

If you're getting the problem under load, and under boost, I would re-visit the headgasket again. Make sure your fan clutch is working properly.

Typically a 12HT will run quite cool until under a moderate load.

I have never heard of a turbo pushing air into the cooling system - a turbo that runs at maybe 10 PSI of boost pushing air into a water jacket that runs at 13 PSI, and the whole theory behind how that would happen seems pretty sketchy to me.

~John

 

[Tapage]

sad to said .. but I place my bet in head or head gasket ..

Less likely fueling or timing .. but I would stick with my first bet ..

 

[12HTHJ75]

I would suspect a bad radiator or a headgasket.

If you're getting the problem under load, and under boost, I would re-visit the headgasket again. Make sure your fan clutch is working properly.

Typically a 12HT will run quite cool until under a moderate load.

I have never heard of a turbo pushing air into the cooling system - a turbo that runs at maybe 10 PSI of boost pushing air into a water jacket that runs at 13 PSI, and the whole theory behind how that would happen seems pretty sketchy to me.

~John

Thanks, I do need to refill the viscous coupling on fan clutch and will check water pump and flush radiator & cooling system and see if that helps before I start striping head.

 

[12HTHJ75]

Refilled the fan clutch, flushed the system and everything seems to be working fine.
Thanks for all the advice.

 

[12HTHJ75]

It was the head gasket. Had a hole burnt from the No 5 cylinder to the water jacket. Driving to work and it blew the top radiator hose off the thermostat housing, let it cool then refilled to try to get it home but water got into the cylinder and hydraulic locked the engine, luckily it wouldn't let it start.
Dragged it home, put a new VRS kit in it and haven't had a problem since.
Re-tentioned the head bolts at 1000km (I don't think that was done to the previous gasket). Always remember to re-tention the head bolts.