Coolant temperatures while towing

[1998_K1500_Sub]

AC core and radiator fins not plugged full of God knows what from the last few decades? AC fins not all smashed over thus restricting airflow?

Inadequate / compromised water pump flow?

Excessive / unnecessarily high coolant flow through heater circuit?

 

[Road Trip]

I recently bought this 95 suburban 2500 7.4L and Ive done everything possible to try and get it running cooler such as flushing and backflushing all the cooling system inlet/outlet tubes, installing a lower temp 180 degree thermostat (and testing it before installation), making sure none of the coolant hoses are kinked, properly bleeding air out of the system, testing the temp sending sensor for accuracy.....but still on a hot day driving uphill just for 2 miles the temp will reach 230ish even while blasting the heater. The only thing left I can think of is a bad coolant temperature sensor or remove the dual electric fan conversion installed by the previous owner and get a heavy duty clutch fan. What do you guys think?

Greetings whataTRUUUCK,

Welcome to the GMT400 forum! There's a wealth of talent in here -- enough so that it takes
awhile to sort out exactly what everyone's specialty is.

Good news -- we have a few Subject Matter Experts in here who have not only hot-rodded their
cooling systems but have shared all the details on what exact combo of parts can keep a big block
cool while they are towing, and also enjoying the A/C in TX or the desert southwest.

In particular, when it comes to cooling systems all you need to do is replicate whatever L31MaxExpress
is doing. Here's a typical response from him in a detailed thread discussing cooling a GMT400:
(Texas duty mechanical fans & clutches)

Seriously, if you search the site for cooling system upgrades by L31MaxExpress, you will find
some solid discussions where they seemed to pick up where the GM AZ proving grounds left off.
I used to worry about upgrading my big block to the point where it would be tough to keep cool, but
these guys are all over that. No more worries.

Hope this helps. Search around a bit, and then if you come back with a specific question about
a possible best-reasonable-effort combo no doubt they will be able to point you in the right
direction.

PS - As mentioned by others, aftermarket electric fans on your rig is like expecting a 5,000 BTU
window air conditioner to keep up with a 3600 sq. ft. house in Dallas in August. No bueno.

 

[L31MaxExpress]

I recently bought this 95 suburban 2500 7.4L and Ive done everything possible to try and get it running cooler such as flushing and backflushing all the cooling system inlet/outlet tubes, installing a lower temp 180 degree thermostat (and testing it before installation), making sure none of the coolant hoses are kinked, properly bleeding air out of the system, testing the temp sending sensor for accuracy.....but still on a hot day driving uphill just for 2 miles the temp will reach 230ish even while blasting the heater. The only thing left I can think of is a bad coolant temperature sensor or remove the dual electric fan conversion installed by the previous owner and get a heavy duty clutch fan. What do you guys think?

Remove the electric fan garbage. Make sure the condenser is clean. Make sure the radiator is clean inside and out. The 454 fan shroud may be the hardest part to find. A good clutch and mechanical fan is impossible to beat for cooling.

In geographic locations under the rust belt states, with iron heads I would run a 170-180F high flow thermostat myself especially in a hard working truck. All running it hotter than 180F is doing is making the engine more prone to pre-ignition or detonation pulling timing from the knock sensor activity, making the PCM pull timing advance due to the hotter coolant and heating up the intake air which further reduces timing via the IAT sensor.

 

[Cadillacmak]

Remove the electric fan garbage. Make sure the condenser is clean. Make sure the radiator is clean inside and out. The 454 fan shroud may be the hardest part to find. A good clutch and mechanical fan is impossible to beat for cooling.

In geographic locations under the rust belt states, with iron heads I would run a 170-180F high flow thermostat myself especially in a hard working truck.

Listen to L31! It takes horse power to move air, and some engine powered fans can take up to 9hp (maybe more?), which is good. Forget CFM and look at the size of the electric motor on your fan. As an electrician I have dealt with a lot of fans, up to 30 footers to cool refinery operations. You do not move air without HP!

 

[whataTRUUUCK]

You didn't answer my last question.

Im sure the radiator and condenser are a bit dirty cause the truck has been used offroading for many years. However the radiator was recently replaced a couple years ago so thats a bit comforting to know that the fins only have a 1-2 years worth of debris vs 30 years of debris. I need to replace the whole AC system in the near future so ill definitely be cleaning out the radiator fins when I replace the condenser. As for now, ill try the easiest solutions first before the more expensive/labor intensive ones. 1st: test/replace the coolant temp switch on the drivers head and the coolant temp sensor by the thermostat. 2nd a more aggressive cooling system flush with a reputable product such as evaporust. 3rd switch over to the heavy duty stock clutch fan setup.

 

[whataTRUUUCK]

Remove the electric fan garbage. Make sure the condenser is clean. Make sure the radiator is clean inside and out. The 454 fan shroud may be the hardest part to find. A good clutch and mechanical fan is impossible to beat for cooling.

In geographic locations under the rust belt states, with iron heads I would run a 170-180F high flow thermostat myself especially in a hard working truck. All running it hotter than 180F is doing is making the engine more prone to pre-ignition or detonation pulling timing from the knock sensor activity, making the PCM pull timing advance due to the hotter coolant and heating up the intake air which further reduces timing via the IAT sensor.

Thanks for your nuggets of knowledge! I definitely think the clutch fan will make a difference but want to avoid that if possible cause the dual electric fan coversion probably ran the previous owner $300-$400. You dont think a suburban 1500 with the 5.7L will have the same matching fan shroud? I frequently go to my local Pick a Part auto dismantler and will be getting it from there if need be. But unfortunately the big blocks are a bit hard to find

 

[whataTRUUUCK]

Mistake. Put a tested functional 195 degree 'stat back in.


There's no special procedure for that. Air naturally rises to the top, gets blown past the thermostat, and is seen as "low coolant level" in the radiator. Fill the radiator and overflow tank, good-to-go.


The sending unit for the gauge? Is the gauge itself accurate?


Aftermarket electric fans and their shrouds are often a disaster. I'd drop those electric fans like a broken rubber. Does the shroud have openings that allow airflow when the fans are not running, but close when the fans come on?

OTOH, whether you need or want a "heavy duty" fan clutch is still debatable. What is stock on your engine? Regular-duty? Heavy duty? Probably not "Severe duty".

And there are fan upgrades to go with the fan clutch. Lotsa info on them in the Engine section of this web-site. You'll also need a fan shroud that fits whatever fan/clutch combo you select.

However, are you sure the radiator is OK? Coolant tubes not scaled/restricted? Air fins not corroded?

Why do you recommend the195 degree thermostat over the 180 degree one?

whataTRUUUCK said:
properly bleeding air out of the system,

I believe the sending unit for the gauge is fairly accurate because I comparted the reading by using an infrared thermometer on the thermostat housing. However Id like to do one more test to verify if it should be replaced. I noticed once I shut off the engine the temperature always immediately rises higher (e.g it would read 210 before shut off and then almost immediately read 230-240 upon shut off.....is that normal?

The fan shroud has fixed openings....check out the photo

 

[whataTRUUUCK]

Inadequate / compromised water pump flow?

Excessive / unnecessarily high coolant flow through heater circuit?

Water pump is 1-2 years old and I flushed and back flushed every input/output tube and orfice opening. Coolant is always flowing through the heater cores on these older suburbans cause they dont have a heater core valve like the newers ones. However I heard some people add aftermarket heater valves to improve AC cooling

 

[Supercharged111]

Im sure the radiator and condenser are a bit dirty cause the truck has been used offroading for many years. However the radiator was recently replaced a couple years ago so thats a bit comforting to know that the fins only have a 1-2 years worth of debris vs 30 years of debris.

And if the AC condenser is original then it has 30 years of crud and off road whatever in it and the cleanliness of the radiator is moot.

 

[1998_K1500_Sub]

Coolant is always flowing through the heater cores on these older suburbans

I’ve seen guys put an orifice in the heater lines to reduce the flow, the objective being to direct more coolant through the radiator where heat gets sinked in the airflow.