2006 UD JO8e

[Bsmith8464]

I have a 2006 ud with the jo8e. I’ve been losing coolant. Not a lot, but usually just enough to trigger the low coolant alarm. Sometimes 16 ounces will top if off. The alarm sometimes is on when the engine is cold but after driving a few miles and the coolant starts circulating it goes off. Or it goes off on a right turn (sensor is on the left side of the radiator) so I know it’s not that low. I have always suspected that it was either a small head gasket leak or some other leak with exhaust pressurizing the cooling system. Tonight I topped it off with the engine running and there were tiny bubbles in the coolant with the cap off. Where do I start with troubleshooting this? I’ve heard that head gasket problems are common on these engines, but what’s the chances that it’s something less invasive. Thanks

 

[Hino123]

Water pumps will allow small air bubbles, injector cups will allow large amounts of air. Never seen a air compressor fail yet on a Hino but have seen it on Mack/Volvo/Cummins. Look in the truck corner of the head gasket for red waxy coolant and oil leaks. No real cheap fix, my best guess would be the water pump. Only because the injector cups seem to push it out fast. Water pumps suck air in the shaft and push the coolant at a much smaller rate. Water pump is no small job either. You need to remove the harmonic balancer. If the front crank seal is leaking it would be the time to do it as the seal is right there.

 

[Bsmith8464]

Would the water pump show any visible signs of a failure? Do they suck in air through the weep hole?

 

[Hino123]

You wouldn’t see it. It sucks air around the shaft seal. You could use a combustion gas tester to verify it is not combustion gasses leaking past the head or injector cups. I find that test not very conclusive though.