Truck won't heat up

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mok4200

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Ram Year
1998
Engine
5.9
Truck will not heat up, has brand new heater core and I'm on my 4th thermostat. All started after replacing my plenum gasket. All parts from dodge. Made sure to burp the system and checked all fluids. Any ideas?
 

dudeman2009

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2001 1500 Sport with enough electrical modifications to make my brain hurt
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Magnum 360
If the truck is refusing to get up to operating temperature, you need to verify the gauge reading by either feeling a radiator hose with your hand, or a thermometer. If the radiator hose heats up after about 10 minutes of idle, replace your coolant temp sensor. If the radiator hose doesn't heat up, you need to check for flow from the water pump. That requires taking out the thermostat and running the engine with the radiator cap off. You may be able to test it without removing the thermostat, but there is no guarantee. With the engine running, look into the radiator cap hole and watch the coolant level as you rev the engine by hand. The level should drop when you rev the engine and rise when you let off.

If it doesn't remove the thermostat and try again, or if its already out, you are looking at a new water pump. You could try flushing it before replacing the water pump.
 
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mok4200

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I drove it around for 30 mins and the heater hoses were hot but not too hot to hold onto. I'm going to try to replace the upper and lower rad hoses then try to take out the thermostat and see what happens, thanks for the advice
 

dudeman2009

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The heater core hoses wont be HOT if the core or one of the adapters/lines is plugged or you're running a thermostat at 180* or less.

Whats important is the upper radiator hose. We might be on different pages here. Is your cab heat not getting hot, or is the engine coolant not getting hot?
 
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mok4200

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Both. Last week I got a "too cold for too long" engine code and after that I put in my dodge thermostat, same result. The cab also has very very mild heat, would guess maybe 90 degrees blowing. The upper radiator hose I should replace, when I was changing thermostats it was pretty flexible..
 

dudeman2009

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2001 1500 Sport with enough electrical modifications to make my brain hurt
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Magnum 360
Both. Last week I got a "too cold for too long" engine code and after that I put in my dodge thermostat, same result. The cab also has very very mild heat, would guess maybe 90 degrees blowing. The upper radiator hose I should replace, when I was changing thermostats it was pretty flexible..

It is a slight possibility, if someone just put straight water in at some point and ran it like that for awhile, that there is a type of scale buildup that is preventing heat from transferring to the coolant. At this point, i'd put in a coolant flush additive and run it without the thermostat until it gets up to operating temp for at least 20 minutes, or about 100 miles, whichever comes first. The flush and reverse flush the engine block and forward flush the rest.
 

alanack6795

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Make sure you are installing a Mopar T stat and its being installed the correct way. The thermostat is the ONLY thing that can cause this issue
 
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mok4200

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Make sure you are installing a Mopar T stat and its being installed the correct way. The thermostat is the ONLY thing that can cause this issue

Spring is in the down position, and it is direct from the dodge dealer. I'm going to take it out soon, and then put it in boiling water to make sure it is opening.
 

Max78

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Be sure to check your radiator cap! I replaced my entire cooling system and the cap was the last part that made the most impact keeping the system stable and consistent.
 
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