MJ Still Running Cold

[summerinmaine]

As I mentioned in a previous thread, I appear to have the opposite problem from most cooling system complaints I've read. My MJ still has the stock closed cooling system, and the engine temp rarely gets above 160F (according to the gauge and confirmed a few times with a pyrometer). And it's not like we have cold weather down here.

 

About the only time the temp gets close to 200F is on a really hot day, under load, and stuck in traffic. :dunno:

 

Pulled the thermostat (which looked real old and may have been the original) back in November, and put in a fresh 195. No change.

 

Just pulled that thermostat yesterday, and put in a different 195. Again no change.

 

Each replacement thermostat has the bypass hole, which I understand is correct (i.e. shouldn't cause excess cooling). Is there any other bypass in the cooling circuit that might be flowing excess coolant? I'm scraping the bottom of the thought barrel here.

 

My fuel economy is down around 13mpg, which I assume is due to the ECU system never getting out of the closed loop. OTOH a plug check (not a chop however) showed nice light chocolate colored electrodes/insulators.

 

I'm almost ready to slap a baffle over part of the radiator.

 

Any other thoughts?

[HOrnbrod]

Have you verified the accuracy of your temp gauge with an infrared or laser portable thermometer? These gauges are far from precision instruments. :D

[maddzz1]

Mine does the same thing; barely above the 160* mark. I put a new 195* thermo in last summer but had idiot lights then. Since I switched to gauges it has run like this. I figure it may be the gauge itself, and if not, it is better than the alternative.

[Jerry]

My V6 was running cold, I tried a new thermostat, no joy. And I even got to the stage of covering the radiator with a piece of cardboard! When I did this I noticed the oil pressure was dropping off noticably indicating the engine/oil temp was rising above normal. My last resort before replacing the gauge was to go through and clean up all the temperature sensor electrical connectors in the engine bay. Success!! Maybe worth a try for you, mine were all gummed up :thumbsup:

I guess that the voltage in the temp gauge system rises with temperature which is why it appears to work correctly when the engine gets real hot and therefore the voltage gets to a point where the gauge starts responding properly. It happened to me in the summer crawling up a mountain pass in +30C with the camper onboard plus a cab full of people and gear :yes: the gauge suddenly started to show a big increase in temp. Never went into the red though, good truck! :bowdown:

 

edit: As above also :agree: worth getting a suitable workshop temperature gauge and seeing what the running temp actually is right next to the sensor on the head/manifold. I did this and it show around 84C which is what the thermostat is rated at.

[summerinmaine]

Have you verified the accuracy of your temp gauge with an infrared or laser portable thermometer? These gauges are far from precision instruments. :D

 

Yep. Verified with a pyrometer (i.e. infrared thermometer).

[summerinmaine]

Mine does the same thing; barely above the 160* mark. I put a new 195* thermo in last summer but had idiot lights then. Since I switched to gauges it has run like this. I figure it may be the gauge itself, and if not, it is better than the alternative.

 

Agreed. But it is disconcerting to be bushwacking at 10mph in the desert on a hot day, and have the engine running cold.

 

Plus, I'm the kind of guy who is compelled to seek out answers to anomalous occurrences.

[summerinmaine]

My V6 was running cold, I tried a new thermostat, no joy. And I even got to the stage of covering the radiator with a piece of cardboard! When I did this I noticed the oil pressure was dropping off noticably indicating the engine/oil temp was rising above normal. My last resort before replacing the gauge was to go through and clean up all the temperature sensor electrical connectors in the engine bay. Success!! Maybe worth a try for you, mine were all gummed up :thumbsup:

I guess that the voltage in the temp gauge system rises with temperature which is why it appears to work correctly when the engine gets real hot and therefore the voltage gets to a point where the gauge starts responding properly. It happened to me in the summer crawling up a mountain pass in +30C with the camper onboard plus a cab full of people and gear :yes: the gauge suddenly started to show a big increase in temp. Never went into the red though, good truck! :bowdown:

 

edit: As above also :agree: worth getting a suitable workshop temperature gauge and seeing what the running temp actually is right next to the sensor on the head/manifold. I did this and it show around 84C which is what the thermostat is rated at.

 

Been there, done that. Everywhere we checked with the pyrometer showed low temps.

 

BTW AFAIK typically a temp gauge sending unit is a variable resistor (i.e. potentiometer) that varies the resistence (and thus current flow) with temp changes. I assume the MJ is similar.

[HOrnbrod]

That's correct. The sensor is actually called a thermister and varies resistance according to the temp it sees. The gauge cal figures are:

 

1365 ohms = 100°

93.5 ohms = 220°

55.1 ohms = 269°

[summerinmaine]

That's correct. The sensor is actually called a thermister and varies resistance according to the temp it sees. The gauge cal figures are:

 

1365 ohms = 100°

93.5 ohms = 220°

55.1 ohms = 269°

 

 

Thanks.

 

So, given that my temp gauge is accurate, and three failed thermostats in a row would be a bit unlikely, any idea why I'm running cold? :dunno:

[deziped]

Out of couristy have you blocked off like 1/2 the air flow thru the radiator with a piece of cardboard to see if the temp would go up? I had a diesel once that was acting like your vehicle. All the guages, thermostat, etc. were working properly, but, the only way I ever got it up to heat was by cutting the air flow. Just left it in year around. No explanation of why it did it. :dunno:

[HOrnbrod]

Sounds like you gave tried everything except this:

 

http://gojeep.willyshotrod.com/HowtoRadiatorRestrictor.htm

 

Might be worth a shot - can't hurt.

[summerinmaine]

Thanks for the suggestions. A restrictor or a baffle is my next "try" but I'm still mystified as to why this should occur. :???:

[HOrnbrod]

I have no freeking idea. You are definitely one of the few. :cheers:

[oldrusty]

I just went through the same thing with my brothers 2000 ram. Couldnt figure out why the engine wasnt getting up to temp. He had the rad replaced at the dealership where he works and after that it seemed to be over-cooling. After replacing the thermostat )and then that after market thermostst with a new mopar one) I figured out that the clutch fan on the engine was bad. According to dodge the factory fan should come in at engine temp of around 180 degrees. His was kicking in at 65 degrees. We replaced the fan and his engine temps are back to running right about where they should be( gas mileage has improved quite a bit to).

[maddzz1]

I just went through the same thing with my brothers 2000 ram. Couldnt figure out why the engine wasnt getting up to temp. He had the rad replaced at the dealership where he works and after that it seemed to be over-cooling. After replacing the thermostat )and then that after market thermostst with a new mopar one) I figured out that the clutch fan on the engine was bad. According to dodge the factory fan should come in at engine temp of around 180 degrees. His was kicking in at 65 degrees. We replaced the fan and his engine temps are back to running right about where they should be( gas mileage has improved quite a bit to).

 

This is a good idea. I will have to check and see when mine comes on. I also had to put a new radiator in a while back, the old one had become 75% see thru due to all the fins rotting away. I wish i had had gauges back then instead of idiot lights so I could compare before and after.

[summerinmaine]

I just went through the same thing with my brothers 2000 ram. Couldnt figure out why the engine wasnt getting up to temp. He had the rad replaced at the dealership where he works and after that it seemed to be over-cooling. After replacing the thermostat )and then that after market thermostst with a new mopar one) I figured out that the clutch fan on the engine was bad. According to dodge the factory fan should come in at engine temp of around 180 degrees. His was kicking in at 65 degrees. We replaced the fan and his engine temps are back to running right about where they should be( gas mileage has improved quite a bit to).

 

That's a good idea! Thanks! :thumbsup:

[Jerry]

Take out the viscous fan temporarily and see if that makes any difference? :dunno:

[HOrnbrod]

It's difficult to tell exactly when the mechanical fan vicious clutch kicks in since it spins all the time. I suppose a replacement clutch would be in order especially if you still have the original. Usually when they go bad they just freewheel and you overheat. Even if the fan was running full time locked in the thermostat should still keep the engine running close to it's rated temperature, but it's not. Weird. :roll:

[summerinmaine]

Mine has the engine fan (controlled by a viscous clutch, right?) and the auxiliary fan (electric, controlled thermostatically right?). I can't see how a failure of the viscous clutch would cause excessive cooling, unless it locks into a permanent engaged state. Failure causing a freewheel state makes more sense to me. :dunno:

 

Perhaps the auxiliary fan is kicking in inappropriately? Maybe I'll start by inspecting it on start-up (should not spin, right?) and perhaps disconnecting it for a trial run.

[oldrusty]

I had never seen one fail engaged but apparrently it does happen.We tested my brothers by pulling it off and setting it outside in the cold( temp was about 15 degrees). When we brought it inside the hub was very easy to turn ( fan would basically freewheel if you clamped the hub in the vise). We kept checking the surface temp of the hub with my laser thermometer as it warmed up. When it got up to about 70 degrees it got very hard to turn ( fan was engaged). We tested it like this 3 more times and each time got the same results. He figure might as well replace it ( everything else in the cooling system was new) and afterward the engine temps are within 10 degrees of what they ran before he started having problems.Like I said his gas mileage improved improved noticeably wich would make sense if the fan was engaged basically all the time.