Cooling issue: "overcooling"

[badgerd]

This has been an issue for a couple months on my 87 998 with 6.2. Started with "fan will not come on" but wasn't overheating. I used the TM to troubleshoot the fan (as that's what I thought it was):

1. Pulled fan switch, boil tested and opens around 215. When disconnected, fan operates.
2. Disconnect TDM from Cadillac valve, fan operates.
3. Pulled thermo, pop test showed stuck open. THIS HAS TO BE MY PROBLEM.
4. Replace with new OEM. Fan doesn't come on but wasn't running much for a couple weeks... Hot day take it for a 14 mile run at 55, no fan, thermo housing at 175 when stopped. Ran it home a couple hours later, 180.
5. Pulled thermo and tested, stuck open. Ordered replacement.
6. Received replacement, pop tested, opens in the 195 by my thermometer. Installed after a system flush and new hoses.

After all that, I still can't get it to go over 180 (not the guage, no touch thermometer), that means no fan. My concern is what else am I missing to get this thing to keep a "normal" 190-210 temp? The truck runs fine with good power.

I am totally lost. Not a HUGE deal that the fan never comes on (but tests that it should), but I'm never getting to temp no matter what the magical temperature guesser on the dash thinks.

 

[Ajax MD]

@badgerd Geeze, people would kill to have your problem.

Did you order a cooler replacement t-stat? Lots of people do, from what I've read. I stuck with the part # in the TM. Also, what type of driving are you doing? I've observed that in steady, straight driving, my fan never comes on but if I get stuck in stop-n'-go traffic, that's what makes the engine hot enough to trigger the fan.

Wait till summer. I'll bet the fan comes on then.

 

[badgerd]

I ordered the one from the TM... I've tried the "stop and go" as best I can during the COVIDs but straight line driving to work and back. I know the whole fan system works (except the crappy temp guage, sure wish I can find a reasonable replacement that is relatively accurate) and I'm not really worried about it, but I want to take it to the beach (2+hrs to the nearest "drive on" beach) and until the fan actually works I'm a little concerned going that far...

 

[cwc]

The fan clutches vary in the amount of drag present. The M998 I am driving currently has a fair bit of drag so the fan is spinning pretty good even when disengaged, and it takes a hill or driving over 60mph to make the fan cycle.

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[badgerd]

The fan clutches vary in the amount of drag present. The M998 I am driving currently has a fair bit of drag so the fan is spinning pretty good even when disengaged, and it takes a hill or driving over 60mph to make the fan cycle.

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It's cycling, I can watch it move in and out (engage and disengage) when unplugging the cadillac valve. Fan system works as advertised, I just can't get the truck to make it come on.

Maybe I'm paranoid that I'll get stuck somewhere because of something dumb...

 

[Ajax MD]

It's cycling, I can watch it move in and out (engage and disengage) when unplugging the cadillac valve. Fan system works as advertised, I just can't get the truck to make it come on.

Maybe I'm paranoid that I'll get stuck somewhere because of something dumb...

What he's saying, is that the amount of drag is causing your fan to free wheel faster and provide more cooling than most other people. That's why you can't get the engine hot enough.

I am amazed at how quickly the fan cools the engine when it engages. If it free wheeled a little faster, it would probably never engage.

 

[TOBASH]

I don't understand...

Are you complaining that you don't have a problem with overheating?

In the Winter you want a minimum temperature, but I've never heard anyone complain that their engine and radiator worked so well that they are worried.

If your minimum temperature is OK, that means your thermostat is not stuck open. If it is stuck open, replace it. You did the test and replaced with new thermostat so that part is taken care of.

As long as you can cold start and run well in Winter, I would not look this gift horse too closely in the mouth, unless I'm not understanding something.

You can short circuit the temp sender to prove the fan clutch will engage, and after that, I would not worry if you don't get to hear a screaming loud fan engage.

Is it possible that unlike the rest of us, you have a brand new clean functioning radiator?

Best,

T

 

[REF]

I would cover 1/2 the radiator with cardboard or a tarp and run it. that blockage should allow the unit to come up to temp and cause the fan to function. When satisfied the system works properly pull the tarp or cardboard off and sleep well knowing your truck is a rare one that runs cool.

 

[Ajax MD]

I would cover 1/2 the radiator with cardboard or a tarp and run it. that blockage should allow the unit to come up to temp and cause the fan to function. When satisfied the system works properly pull the tarp or cardboard off and sleep well knowing your truck is a rare one that runs cool.

That's an excellent idea. It might also lend proof to the idea that his fan is freewheeling a little faster than the rest of us by reducing the airflow.

 

[badgerd]

I’m not “complaining” but concerned there was an issue. I know diesels are designed to run hot, I don't think keeping the temp below 190 is normal. That's the only reason I'm concerned.


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[Ajax MD]

I’m not “complaining” but concerned there was an issue. I know diesels are designed to run hot, I don't think keeping the temp below 190 is normal. That's the only reason I'm concerned.


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I hear you. You're close, though. 185F instead of 190F. See what happens during the summer. I'll bet you get to 195F or so. Do @REF 's cardboard test and see what happens.

In the depth of a really cold winter, you might run around with a 1/2 cardboard blocker to keep the temp up a little bit but you're in Va. Beach not Wyoming. It's not like you'll be running around in double-minus digits.

 

[badgerd]

I'll try the cardboard insert after we get our monsoon... I just want to make sure it works correctly so I can really start taking it places.

After I replace the heater hoses, power steering hoses, and CV boots.


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