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96 jeep no heat when driving
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mickalv
New User
Jan 18, 2009, 12:53 PM
Post #1 of 8
(2618 views)
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96 jeep no heat when driving
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i have a 1996 jeep cherokee 6cyl 4x4 with 100000 mil. if i am in park i have heat in 15+ mins but if i start driving i have no heat. i have changed the radiator and the thermostat.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 18, 2009, 1:53 PM
Post #2 of 8
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Re: 96 jeep no heat when driving
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Did this do this before the radiator and thermostat? Why were they replaced?
What temps are you dealing with and is the temp gauge holding ONE steady temp once warmed up?
T
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mickalv
New User
Jan 18, 2009, 8:57 PM
Post #3 of 8
(2613 views)
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Re: 96 jeep no heat when driving
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if im in park temp will reach slightly pass 210 which is mid way then fan will kick in and maintain at that level with good heat. once i start driving temp needle starts to drop and also heat. the temp needle will go up and down,gradually, between midway and quater way while driving with little to no heat. radiator was leaking and so it was changed last year with previous owner. (the previous owner also told me he used leak stop before he replaced radiator if that would help.) when i noticed no heat, i had the thermostat changed.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 19, 2009, 1:28 AM
Post #4 of 8
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Re: 96 jeep no heat when driving
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OK: Perhaps that just nailed it down - nice reply.
It would throw more heat with the higher temp till it overheated totally which it doesn't seem to and temp coming down when you notice fan(s) come on is great - so far. It's a bit late so I question the accuracy of the sensing switch which I think is set to about 170F or so. Certainly not over 220F as you've seen. I believe the accuracy of the gauge right now.
The real key is that a sealer was used before. Who knows what type and how much really? Only thing to do is flush it out. Most of those things are "sawdust" based cloggers and can work in some cases but not suggested for most or a permanent fix. {Quite literally - common ground pepper can do the same thing!} THAT COULD BE DELAYING THE REACTION OR SENDER INFO TO TRIGGER FAN!
I'll go look and see how much that switch is as I think I'd replace it and not just clean it with a system flush to get the goo/sealer out of it,
T
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 19, 2009, 1:37 AM
Post #5 of 8
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Re: 96 jeep no heat when driving
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Arggh! I'm not finding a temp switch (should be sensing coolant at radiator not just the two wire one at thermostat but that may act for both??) just a coolant temp sensor?
Does this in fact use only an electric fan, belt driven fan only or belt driven fan with aux electric fan for radiator?? Dunno from here,
T
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mickalv
New User
Jan 20, 2009, 5:46 AM
Post #6 of 8
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Re: 96 jeep no heat when driving
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it uses a belt driven fan. the other fan (i believe is for a/c) is electric.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 20, 2009, 6:57 AM
Post #7 of 8
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Re: 96 jeep no heat when driving
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This is tricky as you well know.
In essence it shouldn't matter how well radiator works or how much fan power they get when it can get too cold?? Too hot can mean lots of things but a too cold reading almost always suggests thermostat is not stopping the flow of coolant to the radiator as it should. Some are made with tiny "v" grooves or "jiggle" valves to assist in purging air out of engine side of system and possibly if somehow too much 'trickle' of flow can pass while cold it is enough to cause engine temp to fall below prescribed temp.
Basics: When all proper the coolant inside engine is heating up with the running engine, constantly being circulated by the water pump within itself for uniform engine temps. The thermostat is placed where it would likely get the warmest of the mix and bypass systems are designed to see that it gets both mixed within engine and that thermostat gets the true temp of that side's coolant. When temp opens thermostat it is then going on thru upper radiator hose to be cooled at radiator, cooled there for return. All the time the water pump is still mixing the internal engine coolant such that it stays even and will then shut thermostat when complete or stay partial as needed with the heat load produced.
The heater is in this mix in that it too takes heat away from the hopefully uniform temperature coolant from within the engine and is able to contribute to cooling the engine some but not generally enough to lower the engine temp by itself alone.
The engine doesn't produce heat or dissipate it evenly by itself so relies on the bypass system and water pump's effectiveness to maintain that.
Voila! Now, if coolant can hide hot spots or system is clogged in any way in out-of-site places it might suddenly throw hot coolant to thermostat, cause instant opening and waits till it's happy with returned lower temp coolant and shuts.
A few things can cause this oddity.
* Water pump unable to pump adequate flow to mix and deliver coolant. Belt could be too loose or impellers of pump impaired in some way - corrosion or some unseen fault or clogging.
* Many heaters are part of the mixing of coolant. Not sure if this one is or not but let's base this on it is. Any flow problems to heater can effect the engine's steady hold on uniform temp. I tend to believe your gauge reading as it's consistent with the heater performance. It too gets it's reading close to where heater hose (warm/inlet side) gets its coolant.
** Suspicions right now for me are the thermostat is bent, clogged or just plain NG. Water pump may be clogged or impellers disabled to some degree. Possible overuse of gasket cements for parts already replaced could be screwing up proper actions. Rare now but return hoses from water pumps can collapse causing all kinds of erratic behaviour. Longer lower return hoses frequently use a spring inside to prevent that and many aren't replaced with the replacement of a lower hose if ever done.
More: If a hot spot in a remote area can boil undetected by gauge or seen it effectively is AIR in the system which is a total headache to both figure out and pin point why. Head Gaskets are a huge reason for "air" (vapor really) being introduced and that just becomes its own diagnostic havoc.
Belt driven fan uses a fan clutch no doubt and in heating season is rarely a problem with adequate cold air around. Simply air speed of moving along is frequently enough without a fan at all. Any obstruction to air flow must be considered - debris, leaves, bugs and any missing air dams/shrouding that channel air thru radiator and create the flow over engine and out below it.
I'd be flushing the whole system out taking note of condition and debris that comes out, replacing thermostat yet again and make certain gasket and ports are clear. I'd seriously consider removing water pump to see if all is well there too.
Consideration should be taken to be sure antifreeze is not too strong. I've said it multiple times here and elsewhere that pure antifreeze (ethylene glycol types) are lousy for heat transfer and add little to raising boiling points which manufacturer's love to boast but it's misleading as it's pressure that's 90% responsible for raising boiling points NOT the product! The lousy heat transfer of excessive coolant will cause hot weather problems and can cause erratic performance any time,
T
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mickalv
New User
Jan 20, 2009, 11:16 AM
Post #8 of 8
(2588 views)
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Re: 96 jeep no heat when driving
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Thanks for the great advice! I will check it all out and let you know what happens.
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