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jimsfordgarage

coolant loss

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1999 Monaco diplomat with cummins iso 5.9l it looses about 1gal. of coolant every 100 miles. it never over heats and has been press tested but can find no leaks  and no smoke from exhaust. also no coolant in oil,

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Actually,   pressurize the cooling system and look for the leak.  A gallon per 100 miles is significant enough that you will find it.

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Has you oil level increased? A head gasket leak is also a possibility and might not be as easy to find.

Pressure  testing already mentioned will find most cooling leaks. Water pump seal leak is difficult to see in Pusher coaches. 

Rich.

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There are lots of places to search for leaks, especially if you have an Aqua Hot or similar device which is tied into the engine coolant, a driver's heater, or anything else that brings coolant out of the engine bay and into the forward areas of the coach. Ours had a small leak in the circulating pump which was used to bring coolant to the front so that the defroster could get heat. See if you can find the route of the coolant hoses running from the engine bay forward, if you've got them. Check the defroster's heater core as well as the driver's heater core (they may or may not be the same).

You many have to really search for the leak, but if you're losing a gallon every 100 miles then it's going somewhere. Best case is you find the leak and can fix it. Worst case is that you're losing coolant through an internal leak in the engine (head gasket, cracked block, etc.)

Like the others have suggested, pressurize the system and leave it for a few days. If the leak is external you'll find it. If it's internal to the engine the oil level is likely going to go up as the coolant leaks into the engine.

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Richard, Good thought!  Totally forgot about the front heater supply hoses, heater core and the supply valves. I had to fix the one on the return line, on our coach that was located on the drivers side, at the middle of the engine and about the same level that the oil pan bolts to the engine.  The supply side valve is located at the back of the engine - engine head. They look just like an outside water faucet in our case. 

Rich.

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