01 Suburban 2500: Thermo not opening?/plow overheat

[Anti_Rice_Guy]

Ok so my dad's truck, pretty much since new has had this issue. If you have the plow on and don't let it get close to operating temp before you start driving, it will start overheating after about 20 min, regardless of terrain or how high the plow is. It will start going just above 210, then the gauge will start booking it towards 260 in a matter of like 20-30 seconds.

Mind you, if you pull off, shut it down, restart quickly and let it idle with the plow down on the ground, it'll cool down to regular temp (just under 210) in about a minute or so, and as long as you don't shut off the truck again, you could drive through a huge hill in the Sahara and the temp gauge wouldn't budge.

Background:
6.0 motor was replaced under warranty and send back to GM at 33k miles due to a random rattle not found and literally like 3psi of oil pressure at idle, and maybe went up to 10-12 under throttle. Truck now has 188k miles. Is equipped with the tow/haul and plow packages.

Thermostat was replaced 2 years ago in an attempt to solve the issue and hasn't change anything. It seems like the thermostat isn't opening right or something.

[sweetbmxrider]

Let it do the overheat thing then grab the top hose or take its temp. If its cold then the t-stat isn't opening. Could be the clutch on the fan is fouled up and not tightening when hot causing it not to spin faster. You could let the truck get to operating temp, shut it off, and try turning the fan by hand. If it freewheels relatively easy, I'd look into replacing the clutch fan. It should be tight and harder to turn when its hot and freewheel when cold. Only other thing is somehow the plow is obstructing radiator flow but I would think the overheating would be constant with it up then. Possibly some clogging inside the radiator, damn dex-cool!

Only relative tsb I saw....

File In Section: 01 - HVAC

Bulletin No.: 00-01-38-010

Date: October, 2000

INFORMATION
Subject:
Proper Positioning of Lower Radiator Baffle When Diagnosing Poor A/C Performance

Models:
2000-2001 Chevrolet and GMC C/K Utility Models
(Tahoe, Suburban, Yukon, Yukon XL)

Prior to performing any air conditioning (A/C) diagnostics to determine poor A/C performance, the lower radiator baffle should be inspected. A contributor to poor A/C performance at idle and/or low vehicle speeds in city traffic, as well as increasing the coolant temperature, may be an out-of-position lower radiator baffle. The baffle is attached to the radiator support assembly and must be positioned between the top and bottom edges of the bumper. This position is critical because the baffle prevents hot engine air from recirculating through the condenser and the radiator. If the baffle is found to be out of position, push the soft baffle up above the bumper's bottom edge. No fasteners are required to secure the baffle. There is no need to evacuate and recharge the A/C system. Evaluate A/C performance following published Service Manual procedures.

edit:

This explains fan clutch operation. Might have an issue with the fluid not properly heating.

The cooling fan clutch may be described as a continuously variable clutch. If the vehicle engine is running, the fan blade is always turning unless the fan clutch is non-functional. The speed of the fan in relation to engine speed is temperature dependent. Maximum fan speed (air flow and related fan noise) through the engine compartment is experienced under two conditions.
1. When the vehicle sits in an unused condition for several hours, the viscous fluid within the thermostatic fan clutch assembly migrates and fully engages the clutch of the fan. After a short drive, the viscous fluid will migrate to the storage area in the fan clutch and the fan clutch will slip, reducing the noise (roar of the fan). This is normal thermostatic fan clutch operation.

2. When the engine is running, and the air being drawn by the fan or pushed through the radiator from the vehicle movement reaches a high enough temperature, the fan clutch will fully engage the fan clutch, drawing additional air through the radiator to lower the engine coolant temperature and A/C refrigerant temperature. When the cooling fan clutch fully engages, fan noise increases (for example; this is the same as switching an electric household fan from low to high speed). Some customers have interpreted this sound increase to be an increase in the engine RPM due to transmission downshift, transmission slipping, or TCC cycling. As the engine coolant temperature decreases, the fan clutch will begin to slip, lowering the actual speed of the fan blade and the resultant sound.

[Anti_Rice_Guy]

Thanks, I'm going to try this tomorrow and let you know how it works out.

Or next time it snows since I forgot I took off the plow last night

[madness410]

are the fans on at all times regardless of the plow position?

[Tru2Chevy]

Originally Posted by madness410

are the fans on at all times regardless of the plow position?

It's got a clutch fan, not an electric.

- Justin

[Anti_Rice_Guy]

That still doesn't really explain how it's only the first time on startup though. Seems more like a hose is pinched when the plow is over the front of the truck, and once fluid goes through it the hose maintains its shape and is fine - the truck will NOT overheat once we get through that problem the first time for the rest of the time.

[sweetbmxrider]

the clutch fluid may not be warming up properly causing poor cooling at higher temps. its just a hunch though. I initially thought a pinched hose but you would have seen a leak by now from the abrasion.

[wretched73]

could the thermostat be sticky? and sometimes open all the way and sometimes get stuck and only partially open? drop it in boiling water to see if it pops completely open? Not sure if that could exactly happen, but i also dont know how dex cool effects the cooling system

[greenformula92]

thats really odd....ive never heard of this before....is the temp. reading accurate? it is possible you are getting a false temp reading.....just a possibility

[Stevoone]

Looked around on google a little, most people are talking about a HD clutch fan and some others are talking about the air shrouds. Someone mentioned a service bulletin but I don't have access to GM Service Information anymore.

The thermostat is on the water-pump assembly and the temp sensor is on the drivers side head. Is it possible that the engine is heating up unevenly? When you run with the plow and the increased load on the engine the block/heads may be heating up too fast to trip the thermostat. Not positive how you would fix that. lower temp thermostat, block heater or just continue to warm the truck up before you use it with the plow.

[Anti_Rice_Guy]

Originally Posted by blk95formula

thats really odd....ive never heard of this before....is the temp. reading accurate? it is possible you are getting a false temp reading.....just a possibility

Must be at least somewhat accurate, because when it says it's overheating the check coolant light comes on, and the engine lets off way more heat waves/heat in general than under normal operation.

Originally Posted by Stevoone

Looked around on google a little, most people are talking about a HD clutch fan and some others are talking about the air shrouds. Someone mentioned a service bulletin but I don't have access to GM Service Information anymore.

The thermostat is on the water-pump assembly and the temp sensor is on the drivers side head. Is it possible that the engine is heating up unevenly? When you run with the plow and the increased load on the engine the block/heads may be heating up too fast to trip the thermostat. Not positive how you would fix that. lower temp thermostat, block heater or just continue to warm the truck up before you use it with the plow.

Interesting.

I'm going to try what Adam said about the fan tomorrow when the plow is on for the coming snowstorm.

[greenformula92]

just threw that out there. every other suggestion makes sense too. to mee the fan clutch and shroud make the most sense to me

[Anti_Rice_Guy]

I let it overheat on the way home from dinner and touched the hose on top...it was warm. not hot, not cold.

I'll check the fans tomorrow, I forgot about that

[sweetbmxrider]

Try turning the fan dead cold so you have some reference. It should spin pretty easy while hot will have significant resistance.