runs hot above 2500rpm

[docdray]

heres the deal, truck in sig line. last oct did 97 coolant upgrade and duramax fan, externally cleaned rad and condensor. just hauled measley 7k lbs in 105 heat. truck empty runs 185 degrees but this weekend ran 220 degrees flat ground under 2500 rpm at 64 mph or less 750 to 900 egt. over 2500rpm it ran 225 to 250 degrees steady with egt at 815 to 1100 flat to mild hills. Is original rad, I am going to pull and vat the rad, is it possible it needs to be replaced, is the fan clutch adjustable, any other reasons it is running this hot besides bad radiator? boost is running 7-9 psi. even b4 upgrades it ran 220-230 pulling loads.

 

[iamdave0887]

if you had your truck at 250 degrees the least of your problems will be the radiator. anything above 210 is hitting the true red zone. 250 degrees is into the "oh crap" zone which is way past red. if you didn't crack a head or the block i'll be amazed. the truck shouldn't be running that hot, period. i've had 4K in the truck bed with my 96(factory upgraded cooling) and the temps never went above normal and thats with a worn out(never heard it engage once since i bought it) fan clutch. somethings not right with your cooling system and i'd say go over the entire thing before you've got to buy new heads or a new block.


is the fan clutch stock? i've heard that when the fan clutch kicks in its easy to hear it. you can get an aftermarket fan clutch that kicks in at a lower temperature. i know both heath and kennedy sell them. not sure on specs however.

 

[Matt Bachand]

I notice mine runs coolest and pulls strongest without temps/egt's climbing skyhigh if keep rpm's @ 2000. 2500 is above the peak/HP effficiency spot, so i think pulling at those levels is ineffecient. Do 2k rpm, might go slower, but it is what it is.

 

[docdray]

with 410 gears running 2k is too slow-close to 50 mph, average temp loaded is 215. truck runs fine, no pressurized coolant system, no coolant loss. even before coolant upgrade, truck ran same temps. egt @ 900, coolant @240. thought has occurred that new tstats are malfunctioning or radiator shot-red is 260, never had engine in red zone, at most one mark shy which indicates 250

 

[Turbine Doc]

pull stats put em in a pot of boiling water to test them, should open fully just berfore water begins to boil, use a candy thermometer or other cooking thermometer to know exact temp they are opening up, you said rad is clean how did you clean it, also is ac core clean, yes fan clutch is replaceable, and IMO is suspect if you haven't changed it before now.

 

[Matt Bachand]

Don't go by the factory guage marks on where RED is. Danger zone is aroun 220-230. Over that and your own borrowed time.

 

[docdray]

one problem down, a buddy who helped said he filled w/ straight antifreeze. drained and added 2 gal distilled water.

 

[mfgguru]

Remember that 7k of weight isn't much, but wind resistance is more of a factor. The sail boat effect sucks a lot of power. Not sure what you were hauling.

 

[JiFaire]

Now THIS subject, I know something about...

There are a number of things you can do to make your 94 run nice and cool with that load... the short list looks like this:

a) pull and clean rad (and coolers) thoroughly
b) check your thermostats (since you already changed to a 2-tstat system)
c) replace your fan clutch and possibly your fan
d) proper water/glycol mix and a couple bottles of water-wetter
e) TCC Lock mod

Want the 3-step details on any of these?

Rad Clean
Start on a Saturday morning... it will take about 3-4 hr to do this right.

Buy:
- new hose clamps
- GENUINE AC Delco thermostat (for single t-stat systems this is a must)
- Heath SD Fan Clutch
- 2 bottles RedLine Water Wetter
- 2 gallons of Top quality Antifreeze/Coolant
- 1 bottle of 'scrubbing bubbles' bathroom cleaner.

Set up shop in the driveway or someplace where you can clean the rad, then get the hose and wash away all the crap you get out of it... bugs, sand, little rocks, leaves, dandelion fluff, slow hitch-hikers, politicians, etc.

1] definitely pull your rad and clean it properly. Yes, it has to come all the way out. No, it isn't that big of a deal.

- drain rad - 5 min
- pull shroud - 5 min
- undo clamps, hoses, rad lines - 5 min
- pull grille (top bolts, front clips, a couple screws behind signal lights) - 15 min
- lift out the rad, place it face-down on a couple of sawhorses or 5-gallon plastic pails, and start washing it out from back to front... use a sprayer on a garden hose (you can bend stuff with a pressure washer), spray it clean then spray it with foamy cleaner (I like 'scrubbing bubbles bathroom cleaner), let it soak 15 min while you clean the AC, Tranny, oil coolers. Go back and wash it all out again. Twice. Use a leaf-blower or compressed air (Carefully!) to blow out the sand, dirt, little rocks, etc.. when it is shiny-clean, it's ready to go back in.

These things hold an AMAZING amount of crap... this is going to make a serious mess, so if you can do it someplace where you can just spray away the crap you get out of the fins when you're done, you can stay out of trouble with the little woman. Plan ahead, and don't start the job out on the patio or someplace like that. I like to use my neighbor's driveway.

2] check the fan clutch. If it is stock and especially if you've never heard it (it sounds like a jet engine taking off under your hood when your truck gets hot while towing), it probably needs to be changed... yes, they DO wear out. Here is a description of the different fan clutches... you want one that is either HD or SD. Get one that is calibrated to kick in a little sooner than 210 (Heath's is calibrated to kick in 10-15 degrees sooner, and is a high torque-transfer clutch, which means when your engine is doing 2000 rpm, your fan will be doing a large % of that... not so with all clutches ... ask if this statement is confusing and I'll explain further). Note that they kick in at a pre-set AIR TEMP, not water temp. The air temp is usually about 10* lower than your rad water temp, so if it says it kicks in at 190-195*, that means about 200-205* water temp. You want it to kick in BEFORE you overheat, not after.

Think about changing your fan.. the 94 6-blade metal fan can be replaced by a 2000 9-blade metal fan, or a 9-blade composite DMax fan, both of which move considerably more air.

3] replace the thermostat. Make sure you use a GENUINE AC Delco thermostat... (for a single T-Stat system, there is no other acceptable brand... there is a plunger-bypass needed, and they must be high-flow. You ignore this advice at your own peril.) For a 2-tstat system, RobertShaw makes good thermostats, too.

- do it all back up, replace the crappy GM hose clamps with the new ones you bought, pour in 2 bottles of Redline Water-wetter and fill with 50% antifreeze mix. Burp system as required.

TCC Lock Mod
You're lucky... since you have an OBD-I system, you can put your Torque-Converter on a switch to force it to lock up, which will make your transmission run a LOT cooler when towing, and has the added benefits of giving you engine braking in the hills. That's a topic for another thread, but if you're interested, let me know and I'll write something up.


Before doing all this to mine, I overheated on a sunny day in January. Since this, I pull my 30' fifth wheel through the mountains in BIG ambient heats with the AC on... Don't let anybody tell you it can't be done without spending whacks of cash replacing stuff.

But don't let anybody tell you that you don't need to pull the rad, either... do it right, or do it over.

That's my story, and I'm sticking to it.

Jim

 

[Turbine Doc]

Better than scrubby bubbles, is a/c condenser foamy cleaner from local a/c supply shop, and yes to properly clean rad and a/c core it does thake 3-4 hours, especially if you have never done a 3-4 hr cleaning before.

I see trans temp gauges on your rig, what trans temps you seeing, and what are you monitoring pan temp or trans return temp

 

[docdray]

1 have had tcc lock for 3 years and helps quite a bit
2 pulling 5ver
3 in oct 07-engine degreaser and carb cleaner on radiator, condensor, oil cooler,(new tranny cooler), then medium pressure washed. radiator removed during 97 cooling upgrade, installed duramax fan and clutch. 180 tstats.

tranny temps-in ambient air 105, tranny output temp running 220----then runs through radiator, new front cooler(spec for 24k lb load), then to rear stock tranny cooler mounted under truck, then into tranny all through 5/16 line and all synthetic fluid. ((unloaded and tc lock, tranny runs 150.))
4 I believe proper course now is 1-pull and have rad boiled for internal and further external clean, 2-correct coolant w/ 60 distilled water and 40 antifreeze, 3-I always use lube gaurds kool-it. any other ideas?

 

[SnowDrift]

if everything is clean on the outside, then I suspect a plugged inside on the radiator, itself. For the age of yours, I'd suggest just replacing it and being done with it. You'll be surprised at how well it cools.

Yes, test the t-stats and if they're bad then replace them with OEM stats.

 

[Matt Bachand]

To all you other towers, is it normal to drive at sustained 2500 rpm? To me that seems like the problem. But I drive 2k rpm, even if its 55-60.

 

[TurboTahoe]

Amen to Jim's advice - clean that rad!

Also, I drilled some small holes around the periphery of my front grill and installed some nylon screen mesh (the type you put on the windows in your home). I used nylon ties to secure the mesh. It screens out a LOT of the little critters and keeps them out of the rad in the future. You do need to take the front grill off like 1/year and either replace the mesh or clean it (I use either the hose sprayer or a vacuum cleaner).

Rob

 

[JMJNet]

Also put Redline watter wetter or RMI-25.

 

[SnowDrift]

To all you other towers, is it normal to drive at sustained 2500 rpm? To me that seems like the problem. But I drive 2k rpm, even if its 55-60.

That was at 64 mph, so I don't think that's too unreasonable. He's got 4.10 gears and that would put him at near 2000 RPM at 55 or so like you mentioned in your post, if the alternator sheave is the correct diameter.

 

[JMJNet]

Yes, the 4.10 gears is not as efficient as 3.73. It is designed for towing.

This part of Texas has got some hot weather also for about 2 months now.

 

[docdray]

pulled and took rad to shop---#1 problem down, the internal core is poo poo. have new rad on order and test from there. interesting side note, the owner (35years working on rads) says running straight antifreeze is no problem. I wonder how many others agree???

3rd gear @ 55 is 3 grand and screaming, new alternator is same rpm as old alternator. and since my nominal loads are 6 to 9k lbs I am considering going to 373's and heaths new tow chip.

 

[NVW]

pulled and took rad to shop---#1 problem down, the internal core is poo poo. have new rad on order and test from there. interesting side note, the owner (35years working on rads) says running straight antifreeze is no problem. I wonder how many others agree???

3rd gear @ 55 is 3 grand and screaming, new alternator is same rpm as old alternator. and since my nominal loads are 6 to 9k lbs I am considering going to 373's and heaths new tow chip.

I was under the impression straight antifreeze would gel? Leo

 

[JiFaire]

Straight antifreeze has a very high heat transfer coefficient, so it gains and sheds heat slowly, compared to water.

It is only a threat to gel at our Canadian ambient winter temperatures...