fan not kicking on

[1993]

I've been running the engine for about 15min about once a month since autumn. been too busy to get it ready for inspection.
it's been a long winter here in the northeast..
Anyways,
today as I always do, I checked the oil level but also coolant.
The coolant seemed low so I opened the fill cap and it popped off with a good deal of pressure. immediately the coolant level began to rise quickly gurgling back up to the "fill" line.

I ran the engine maybe a bit longer than normal because it was very nice outside and it may have been longer than usual since the last time it ran it.
I drove it around a bit, the temp got to about 200 so I went back to work for about 10 minutes to let the fan kick on(it's the use it or loose it attitude).
anyways, when I got back the temp was 240 so I turned the engine off. the coolant level was at full when I switched the engine off.

I know the fan has worked before.
could sitting prolonged periods cause these issues?
What could be wrong?
Why did the coolant reservoir have so much positive pressure after a month of sitting?

something maybe I should mention is that I last parked it with the front about a foot higher than the rear.

 

[Dock Rocker]

Never ever trust a military gage. Ever.

Verify the temp with a laser or other method before you go to crazy. At 240 you should have had coolant boiling out so my suspicion is you have a bad reading on your gage.


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[LouWon]

As mentioned in the previous message, don't trust the gauge
I just worked on mine today, I replaced the temp sensor since the gauge was erratic, usually my temp gauge would hit 200 and the fan would go on, now it stays at 240, once it its 240 , then fan clicks in.
I checked with my laser and everything is normal, This is just to show you the difference between one sensor and another, or I was sold the wrong sensor
Check the temp sensor near the thermostat and check the time delay, look at the wires, if you can see the bare wires or the insulation is cracked, replace it
I did new hoses, sensors and everything works the way it should, apart from running at 240, lol

Also, pay close attention to the nipples on the overflow tank, remove the two hoses and make certain that they are clear, you can use a small drill bit to clean them up, I forget the size.
They can be partially blocked and can cause big problems

 

[suzukovich]

Make sure all the air is out of the coolant lines. Since truck sat higher then the back. Sounds like there might be an air pocket near the thermostat. Next if been realy cold and the truck been sitting. Take a hair drier and run it blowing on the Cadillac valve. There is a possibility that it's stuck.. Next check the connections from the themostaic switch and or the switch is bad. One other thing. It wouldn't be unusual for the truck to have the wrong thermostat installed. This seams to be a common issue with former NG trucks. Also check the power steering fluid level. Fan clutch is activated by theCadillac valve when the Thermostatic switch sense the Temp is to hot and activates the the fan.. Also you need to really just drive the truck.

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[1993]

Hey Dock Rocker, the thing is that in the past I have in fact witnessed the fan kick on when the gauge showed just above 200.
But I will do as you suggested and use my laser thermometer.

I am concerned about what suzucovich mentioned regarding air in the coolant lines.
It kind of makes sense that the thermostat would malfunction if there is an air pocket.
And as LouWon suggested, I will check those hoses.

at least now I have some leads for my investigation.
Thanks to everyone for responding!

 

[Action]

When the system warms up, pressure builds up. When it cools down, the pressure drops back down. I am just guessing here, but if you have pressure after sitting for a month, it came from somewhere, such as combustion chambers.
When it is cold, open the cap to relieve any pressure. Put it back on. Run the engine for about 30 seconds. Remove the cap. Do you have pressure built up in that 30 seconds?

 

[Retiredwarhorses]

When the system warms up, pressure builds up. When it cools down, the pressure drops back down. I am just guessing here, but if you have pressure after sitting for a month, it came from somewhere, such as combustion chambers.
When it is cold, open the cap to relieve any pressure. Put it back on. Run the engine for about 30 seconds. Remove the cap. Do you have pressure built up in that 30 seconds?

Your not going to build 15psi in 30 seconds...

 

[Action]

Your not going to build 15psi in 30 seconds...

No, but I have seen the motor pressurize the tank in 30 seconds when it has a cracked block or head gasket leak. This could be why his tank did not lose pressure after a month of sitting.

 

[1993]

ok so i haven’t had time to really look into this further yet but your replies got me to go to the truck and at least see the current situation.
after last shutting down of the engine(at about “240”degrees), the level was at the fill line.
right now it was at about halfway up, and when i took the cap off, only a tiny bit of air was released and the coolant did not rise, unlike last time when it filled up within a minute.

 

[1993]

Your not going to build 15psi in 30 seconds...

Well I'm not building 15psi but there is some faint pressure when I open the cap after running for a minute.
I did run the engine with the cap off and stared into the tank for about 30 sec to see if any bubbles show up. did not see any trace.
any other simple ways to rule out head gasket or cracks?

something that I didn't mention before is that I immediately get some heavy white smoke on first startup for about 20 sec and then very small hints as the glow plugs continue to cycle.
I figure it's unburnt fuel?
no smoke once glow plugs stop cycling.
the engine starts up on first crank.
There is some oil seepage from left head cover gasket.

some not necessarily relevant background...
truck(1993) has less than 8k miles, many areas of the truck look like they have never been touched, the inside paintjob looks factory original.
air box is marked up with regular filter maintenance dates and mile readings.
muffler looks almost new. Bottom of truck is not scratched or dented, frame has a heavy black coating behind which the frame metal paint looks amazingly preserved,
there is however plenty of sand in hard to clean areas..

 

[ken]

Yep the white smoke is unburnt fuel. No bigge most like likely a bad or going bad glow plug. Does you fan kick on when you un plug the switch mounted on the drivers side cross over just before the thermostat? unplugging this switch will kick the fan on. The oil leak at the gasket is very common on a 6.2. My Civi engines do that and have ran great for years. I'm with Suzukovith on this one, Try unplugging that switch and report back.

 

[1993]

Yep the white smoke is unburnt fuel. No bigge most like likely a bad or going bad glow plug. Does you fan kick on when you un plug the switch mounted on the drivers side cross over just before the thermostat? unplugging this switch will kick the fan on. The oil leak at the gasket is very common on a 6.2. My Civi engines do that and have ran great for years. I'm with Suzukovith on this one, Try unplugging that switch and report back.

just checked it. yes it turns on immediately.

 

[ken]

Ok then it is highly likely that switch is bad. We know the fan clutch and Cadillac valve are working. So that switch and or the TCM module will most likely need to be replaced.

 

[1993]

Ok then it is highly likely that switch is bad. We know the fan clutch and Cadillac valve are working. So that switch and or the TCM module will most likely need to be replaced.

how best to test the TCM and the switch?

 

[1993]

When the system warms up, pressure builds up. When it cools down, the pressure drops back down. I am just guessing here, but if you have pressure after sitting for a month, it came from somewhere, such as combustion chambers.
When it is cold, open the cap to relieve any pressure. Put it back on. Run the engine for about 30 seconds. Remove the cap. Do you have pressure built up in that 30 seconds?

i was just thinking about this again as i continue to worry.
if there was a head gasket leak or crack, wouldn’t the pressure escape back through it, especially if given a month?

 

[Action]

i was just thinking about this again as i continue to worry.
if there was a head gasket leak or crack, wouldn’t the pressure escape back through it, especially if given a month?

I am no expert on how this works, but it seems like the compression of the engine forces the air or gasses into the cooling system. There is no force to push it back out of the cooling system. The overflow cap opens about 15-16 psi. Anything less stays in it.

 

[1993]

I am no expert on how this works, but it seems like the compression of the engine forces the air or gasses into the cooling system. There is no force to push it back out of the cooling system. The overflow cap opens about 15-16 psi. Anything less stays in it.

but isn’t one of the testing methods for a bad head gasket to do an oil analysis for coolant in the oil?
i saw a video of a really bad leak where coolant actually came out first when draining oil from the pan.
i guess the symptoms vary depending on where and how bad the leak.
im still hoping i don’t have one, but am a bit too cheap to do an oil analysis just yet.
any inexpensive but definitive way to tell?

 

[ken]

Normally when a 6.2 blows a head gasket or cracks a head/block you will get steam and water droplets dripping from the exhaust. If you let it get to 240 you would have had bubbles in the system. Coolant would have boiled in the block. NEVER trust a military gauge. They will lie to you! Yes some do work well, but most are very inaccurate. Still holding pressure after a month? Not really a problem. Just a good sealed system. If you had a issue there would be plenty of pressure in the system to over power the cap and coolant would be coming out. And or plenty of air bubbles in the over flow tank. You will see the coolant level rise and fall when the engine heats up and cools down. This comes from expansion.
How to test the switch? You will need a multi meter to test the resistance. The switch should be "open" when the engine is hot. This is why the fan kicked on when you unplugged it. Drive it to get it hot. Don't let it idle. Using you laser thermometer make sure you have it above 200, shut the engine off and check your switch resistance with your meter. You should get nothing. Meaning the switch should have opened. If not replace it.

 

[teteacher101]

but isn’t one of the testing methods for a bad head gasket to do an oil analysis for coolant in the oil?
i saw a video of a really bad leak where coolant actually came out first when draining oil from the pan.
i guess the symptoms vary depending on where and how bad the leak.
im still hoping i don’t have one, but am a bit too cheap to do an oil analysis just yet.
any inexpensive but definitive way to tell?

You can use something called a combustion leak detector kit. Google search Lisle 75500, you can get them for around $40. It comes in a kit that you place blue fluid into a container with a tapered nozzle you hold in the radiator cap neck, any combustion gasses getting into the coolant will change the fluid from blue to a yellowish/greenish color. In your case, since a diesel doesn't create a vacuum, you'll also need a hand vacuum pump to attach the little hose to. They come with decent instructions an are pretty easy to use.

 

[suzukovich]

I knew how to check the 12338599 Switch, Thermostatic Fan. But the realty was just easier to replace due to cost. I am curious what the TCM(Transmission Control Module) has to do with this. There is also a part number 12338603 Module, Time Delay, Hydraulic Cooling Fan, that connects to the Cadillac valve. (1059-06607-01 Valve, Solenoid Control, Fan Clutch) although my issue was the opposite. I replaced mine and issue was solved.

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