LLY cooling problems

[Rhoward225]

A few weeks ago I had my engine temp get up to around 230 degrees. I've got over 300,000 miles on my LLY now and the engine always runs at 210 which is normal or cooler most of the time. I noticed the clutch on my fan wasn't working and the fan wasn't coming on with the high engine temp. I came to a stop, water was good. Turned the truck off, cranked back up started moving, fan came on and everything was normal. Same thing has happened a couple times since. As of yesterday the fan will not come on at all and w/ the load of work trailer the engine is overheating very quickly! Can someone tell me what controls the fan clutch? A sensor or a relay that might be the cause of the problem. I also replaced both T-stats about about 9 months ago, but didn't have a problem w/ anything until now. Thanks for any help!

[DmaxMaverick]

The thermostats control the fan clutch. Although you replaced them recently, you may want to replace them again. If your results are the same, your fan clutch may be going south. If you can see ANY fluid seepage (traces of oil or grime) from the clutch, it is on the way out.

[Duramaster]

I just had a great experience last week with a high miler!! 300,000 miles equals 300,000 miles of road dirt, bugs, plant debris, garbage build up in the cooling cores!! Ihad to remove the entire radiator/ CAC assembly, separate them and blow out and wash out all the debris!!! What a mess. I also cleaned out the condensor and auxillary trans cooler along with the fuel cooler. Using compressed air alone was not enough. The coolers had to come out. It made a big difference. Before the repair, I could hold a rag upto the grille and the rag would just drop to the ground. After the repair, the rag would get sucked into the grille. Good luck! :)

[Rhoward225]

Thanks for the info guys ! I thought the T-stats might be a problem, I'll be sure and pull them and check......If I remember right one T-stat was different from the other. One having a little vertical tube out the top. I hope I put the correct one front to back. If anyone has any idea of how to determine which T-stat goes in front and back slots feel free to say so.....Thanks,

[killerbee]

IIRC, the housing design prevents you from installing the stats in reverse. The front bypass stat will not go in the rear location. But I don't think you will find that this fixes your problem.

The fan clutch is triggered by ambient air temperature passing by the clutch. It is possible to trigger the fan when the thermostats are still closed however, if you use enough boost on a motor that is not hot. But I digress.

You may need to replace the radiator, at 300K. My guess would be, it just got warmer, and your rad capacity, diminished slowly over time due to plating, permits less coolant flow, and therefore less heat transfer, hence less fan.

Thermostats could be your problem, but not likely if 9 months old and the coorect ones were used. Excess debris would more likely cause slow air movement, and hotter clutch, more fan occurence to compensate. But at 300K, you need to do the duramaster treatment anyway.

I am going with radiator clogged. Have you topped the coolant in the last year? What type did you use. If you used dexcool, then topped off with something else, you may have fallen into the old GM cooling system class action category.

[Duramaster]

Hey Killerbee, please explain the "GM cooling system class action category" comment. I am not aware of a "CLASS ACTION" when referring to DEXCOOL. Thanks. :)

[killerbee]

I am not familiar with the details. There is one or more firms that are proceeding with class action litigation against GM for dexcool issues.

As I understand, it is possible to create a semi-permanent sludge when mixing dex, an organic acid coolant, with variations of old green, high silicate formulas. It requires the presence of heat and dissolved O2, from what little I understand of it.

Most problems occur when your typical owner or "jiffy lube" tops off unwittingly with the wrong coolant.

[Onebigcanuck]

Over the last 3 weeks my temp gauge has been moving up and down for no apparent reason. The dealer just replaced the belts and idler pulleys prior to this happening. Also when pulling up a 6 mile, 6% grade the temp went way over the 100C mark for the first time prior to the fan kicking in. Once the fan was engaged it dropped back to 100. I just turned the 36,000 mile mark.

I wonder if the stats are sticking ??? They have been replaced 2 years ago because of no heat in the winter.

[killerbee]

The cooling system will lose some effectiveness over time and mileage, around 5% a year generally. Some is due to tube plating.

If you are concerned, you might try blowing out your stack. it involves using compressed air to reverse flush debris from each of the stack components. To do it right is not easy. Need to remove the radiator to blow the CAC, then remove the CAC to blow the condenser.

You can do an abbreviated version if you have a really gigh flow air source. Just remove the fan shroud and go to work. This will usually always help the high mileage vehicles.

[Mark Rinker]

Usually always? I sorta absolutely don't understand. :)

[killerbee]

...that does look dumb, even this late at night.:)

[DmaxMaverick]

Like, "kinda' pregnant"

"Is you is, or is you ain't?......"