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Old 11-03-2014, 10:56 AM
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Engine runs cold, won't keep heat in cab

So, my 2000 wj won't maintain heat, and it's gotten to be too cold out not to have it. If i sit and idle up to temp, the thermostat opens up at 195 like normal, and the heater will blow warm, but once i've driven down the road about 5 miles, the engine temp works its way down to about 150 or less (just below the mark in between the 1st and 2nd mark on gauge). Heater fades to blowing cold air as a result. What could cause this?


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Old 11-03-2014, 12:56 PM
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Re: Engine runs cold, won't keep heat in cab

I would say that the thermostat is the problem.
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Old 11-03-2014, 05:21 PM
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Re: Engine runs cold, won't keep heat in cab

Second the above.
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Old 11-08-2014, 11:02 PM
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Re: Engine runs cold, won't keep heat in cab

I don't know. Depending on the outside temperature. Many cars and trucks need a piece of cardboard or bonnets to cover part of the radiator for very cold temperatures. I'm talking really cold though, sub 20F and below. If you live in the Northern or Mountain states you always see big tractor trailers with bonnets that usually just leave a small diamond of radiator open for regulating coolant temperatures and maintaining heat in the cab. If this is a new problem then the thermostat is likely. I've had several cars that really had much better heat when I covered about one third of the radiator with cardboard. Including a Subaru Legacy and a GMC Envoy. Again we get extreme temperatures here in Winter, that sit sub-zero often for weeks during Winter. You really need to pay attention as idling to long will force your engine fan on, but in many Northern states the radiator bonnet is common. Good luck.
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Old 11-23-2014, 07:48 PM
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Re: Engine runs cold, won't keep heat in cab

Check for a hex head plug on top of the engine, usually in a steel block on the drivers side. This is a bleeder. Park on level ground and crack it open and slowly fill the radiator until coolant cmes out the plug. Tighten and run the engine.
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Old 11-27-2014, 12:16 AM
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Re: Engine runs cold, won't keep heat in cab

Thanks. I live in southern AL, so no extreme cold. I replaced the radiator and water pump about 3 years ago, and i think that's when it started, so it might be the bleeder screw or t-stat. I did talk to a mechanic that said it could be the radiator itself. Said they collect rust on the bottom from the engine. The top is hot when engine is up to temp, but the bottom of the radiator is still cold. Would the bleeder be on the manifold (with a rubber cap on it, like the bleeder on a brake caliper), or would it be on the actual engine block?


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Old 11-27-2014, 09:35 AM
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Re: Engine runs cold, won't keep heat in cab

The bleeder is on the block and is a hex head plug. You could always remove the hoses and flush the radiator. I would think if you had a block in the heater you would either have an ectremely high pressure or no circulation thru the engine.
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Old 11-27-2014, 10:24 AM
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Re: Engine runs cold, won't keep heat in cab

I won´t expect air in there 3 years after replacing the pump. I would start with a new thermostat. The fact that it first heats up normally is already a sign that there is no airlock in the heater core.
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