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2012 Hino 338 losing coolant

Jetco

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Hello I have a 338 with 250k miles. First problem is when pulling a hill empty or loaded, temperature goes to start of redline. As soon as you start going downhill it goes back to normal. It also does it on flat roads but towards the end of the day. Changed all the hoses and belts. Thermostat too. Had this problem for awhile but seems to be getting worse. Now it is losing maybe a quart of coolant a day. Seems to be pushing coolant out of the overflow hose that comes out of the coolant reservoir. Coolant reservoir stays full but radiator is low. Also fan seems to be always on. Any help would be appreciated. Thanks.
 

greasytshirt

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Hello I have a 338 with 250k miles. First problem is when pulling a hill empty or loaded, temperature goes to start of redline. As soon as you start going downhill it goes back to normal. It also does it on flat roads but towards the end of the day. Changed all the hoses and belts. Thermostat too. Had this problem for awhile but seems to be getting worse. Now it is losing maybe a quart of coolant a day. Seems to be pushing coolant out of the overflow hose that comes out of the coolant reservoir. Coolant reservoir stays full but radiator is low. Also fan seems to be always on. Any help would be appreciated. Thanks.

The radiator can get very full of debris, restricting airflow through it. It can be difficult to see this. Removing the intercooler to clean the radiator may be a good idea. Also, the fan clutches can be problematic. Do you ever hear it engage? Is the fan clutch leaking a viscous fluid? Spin it by hand. It should have some resistance. If it spins freely when cold, it's definitely bad.

The coolant recovery bottle has a cap with a hose on the end of it. It's really easy to get this hose pointing in a direction other than straight down. The hose will get caught in the shallow end of the reservoir and curve right back up, pointing toward the top of the tank. You'll see coolant going to the recovery tank and never returning to the radiator. Sometimes this hose simply falls off and you get the same symptoms.

I'd check the radiator, fan clutch, and recovery bottle hose first.
 

Jetco

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The hose in the recovery tank is there and pointing straight down.
The fan does not spin freely it turns with a some drag. The fan seems to be engaged all the time. You can hear it running. No oil seems to be on it either.
Tomorrow night I will take the intercooler out and see if there is debris on the radiator.
Thanks for your help.
 

greasytshirt

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While you're in there, see if you can see evidence of the water pump leaking. The weep hole is really hard to see, you might need a mirror on a stick. Sometimes they pull air from the atmosphere and aerate the coolant, and you'll get similar symptoms.
 

Jetco

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Ok took out the intercooler, not any debris but I blew out the radiator and it was packed full of dirt/dust. Drove the truck the past few days, runs cool all the time. Uphill, empty or loaded temp stays the same. The only problem is it is leaking coolant out of overflow tank hose. Seems to be pulling a little coolant out of radiator and into the overflow then out the overflow hose. I can see where it has been running down the side of the fan shroud. When I cleaned the radiator I also removed the overflow tank and emptied it out just to make sure it was clean. It was. I refilled the tank with coolant, to the full line. 2 days later it is nearly full to the top. And the radiator is about a quart low on coolant. Any ideas. Thanks so much for the help on the overheating problem.
 
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greasytshirt

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Well, there's a pretty good chance that the head gasket is leaking. Once you've eliminated all of the other culprits, the head gasket is next. Very occasionally the water pump will cause similar symptoms, so you might want to look at that first.
 

greasytshirt

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If you end up doing the head gasket, have the injector cups replaced at the same time. It's much easier to do them with the head on a bench. Also have the oil cooler resealed. They always leak.
 
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