I have a 90 jeep cherokee inline 6 i have no heat.There is a brand new water pump and new thermostat coolent is also full and circulating.Could the heater core be pluged ..or is there some kind of bypass due to a faulty temp gage or something i cant see..any help would be great .thank's

Run the engine to operating temperature.......thermostat open....
Touch the upper radiator hose, if thermostat is open ,it will be hot to the touch...
Check both heater hoses...should be hot to the touch going in and coming out...if only one is hot,heater core probably is clogged....
I believe this model uses a heater control valve as well.....make sure valve is operating..
Post back findings....

JIm

The engine does not achive opperating temp it stays at about 45 Deg insted of 100 deg.(normal temp)The hoses are warm only .I noticed what looks like a vacume opperated valve between the heater core and the top of the thermostat housing where the core hose connects.I took the hose off this valve on the core side to check for flow (engine off)and it was good. i dont get any vacume to the valve though(engine running).is there some other system that could prevent reching opperating temp...Thank's for your help....

If it doesn't warm up you'll probably notice the upper hose gets warm early from a cold start indicating the thermostat is not closing or slipped and is bent somehow - new or not,

T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/