What to do while I'm at it...

I have a 6.2 with 6.5 turbo in my M1009. I have a gear drive timing set and fluidamper that have been sitting in my garage for years and I am finally going to install them, and fix my front crank seal oil leak while I am in there. I have some questions for things I could do while the frint of the engine is apart and I'm curious what y'all think:

Obviously I have to take the water pump and timing cover off to get to the timing set. The water pump is 4 years old and doesn't leak, but was a cheap $50 unit from Rockauto. I have occasional overheating problems when climbing steep highway grades when its hot out, and at high load offroad (think deep sand). The truck runs fine climbing grades in cooler weather or even when 100+ F if just cruising down the highway. I dont necessarily think the water pump is the problem, but its going to be off anyway. Does anyone have experience with Flowkooler or other "high output" water pumps? Is there any sort of water pump that is an effective upgrade over a stock type, or is it snake oil and they're all the same?

I do want to get a better radiator, and I think this is the key to solving my cooling problems. I currently have an aluminum rockauto radiator with a 1.75" core thickness. I would like something with a 2.5" or thicker core (dont really care how many rows, as aluminum radiators seem to have fewer larger rows resulting in the same core thickness and same cooling performance). Does anyone have a radiator they have had good luck with and would recommend?

I also have a GM1 turbo, which I understand has a fairly restrictive turbine housing and exhuast outlet. I'm running ~6psi and I am very happy with the trucks power and performance. The turbo is in good shape with no shaft play. It cruises 75 mph on the highway with power to spare and I like how fast the turbo spools up when off road. However I wish the EGTs were lower (can get up to 1100F+ if I try to hold 70 mph climbing highway grades, and I have to back off the throttle to get it back down tunder 900F) and I wonder if a less restrictive turbo would help with MPGs. I am getting ready to build a custom exhaust, so if I am going to switch to a different turbo now is the time. There's an overwhelming amount of info on turbos for these trucks out there, and I'm hoping others can chime in and point out anything I might have missed:

• ATT - non wastegated, probably wont spool fast enough for me off road at high elevation?
• GM4, 5, 8 - maybe slightly more free flowing than a GM1, but worth replacing if the GM1 is working fine? Maybe for a GM8?
• HX35 - seems like overkill for a stock compression engine that I'm unwilling to run above 7 psi of boost.
• HX40 - definitely overkill
• anything else I am missing?

What do you consider overheating problems? What temperatures are you hitting on the coolant?

The pre combustion chambers in the stock 6.2 have the smallest throats leading to the combustion chamber of any of the 6.2/6.5 engines. I think there were 5 or maybe 7 different sizes over the 20 year run. I have the largest throats pre cups in my 6.5, the “Diamond” marked ones. I also can hit 1100° if I stay in the throttle with boost above 3 psi on uphill grades. To me it is no surprise that you are. My fix was to add water/methanal injection. I have never gotten over 900° with that system pumping.

There are two links in my signature. 1 is the thread about my turbo diesel truck on this site. The other is to my YouTube channel. I cover the engine coolant temp experience and EGT experiences in both.

Water temps are 195-205 F cruising on flat ground at any speed, or climbing grades in the LA basin, which is good. Right st thermostat temp. When I'm in the mountains or high desert and it's hot out, temps go to 220+ quickly and keep climbing if I try to maintain 60+mph up a long grade. I got to 235 once before I noticed, but ever since have been extremely careful to keep it under 220 and usually under 210 by slowing down significantly and turning off AC.

I have temperature gauges in the front and back of the driver cylinder head, and in the radiator inlet and outlet hoses. Cylinder head and radiator outlet temps all track within 5 degrees at most operating conditions, and always within 10 F. The radiator outlet is 15-30 degrees cooler than the inlet, but when it's hot out and I'm climbing a highway grade with AC on the outlet can get up to 200-205 with engine temps of 225 or more, and I have to slow down and turn off the AC. This leads me to believe the radiator cannot shed enough engine heat, but I could be wrong

I'll check out your content on here, thanks. I often do long road trips of 1000-2000 miles, and it might be hard it carry enough water/methanol mix for that kind of distance. What size tank do you have and how often do you refill it with typical interstate highway driving? And what general part of the country are you in? I'm out west and expect I would use more water on the freeways here then someone in a flatter area

OK. You really are getting hot and you know what is what.

I ended up with the biggest 2 core aluminum radiator radiator.com sells for the squarebody. It helped, but even on our relatively flat terrain I was still getting over 210° on 95°+ days with high humidity while going 70 mph or more with the a/c blasting.

I think GM had the same issues with stock trucks. That is why the 1998-2003 6.5 diesel trucks all got the dual thermostat set up and a water pump with the threaded fan clutch mount built in. Those reverse flow serpentine belt water pumps, fan clutches and bigger fans make a difference. Heath diesel actually has a kit:


I called them up and talked to Mr. Heath. Nice guy to talk with by the way. Their pump, clutch and fan made the difference for me. When the fan clutch gets around 206°-208° the fan goes to 95% lock. I can feel the power loss when it happens. I can also hear it. My water temp will drop within 10 seconds of the fan clutch engaging.

EGT and water injection. I have the 10 gallon tank from nitrous express. Here is a link to the same basic kit I have:


The saddle tank is separate.

I called and talked to nitrous express before purchase. Basically their tech line is 3 or 4 car guys sitting in a room together talking fast cars all day. Great people to talk with that actually put me on speaker when I called back to report how it worked so the others could listen in and join the call. I ended up with a much bigger nozzle than the kit came with.

Once installed I set it to come on at 5 psi of boost. I never got hotter than 850° around Texas. Then I went to Colorado 3 summers ago. The Heath kit kept the engine cool but going up passes I was only using 2-4 psi of boost with all the tight turns and EGT’s were getting too high. We drove 6 high passes. I changed the water injection to come on at 3 psi of boost and that fixed any EGT issues. It also sucked 10 gallons of water in about 1000 miles.


I started off buying distilled water only. I would add a gallon or two of 0° blue windshield washer fluid which is 10% methanol to prevent freezing in the winter. I really couldn’t tell a performance increase with that low of a mix. The last year or two I just put the garden hose in the tank and fill it up. No problems.


To sum up. A high flow balanced water pump, 90% or greater lock up fan clutch with at least a 20 minute duty cycle along with a good aluminum radiator and a proper sized several gallon coolant overflow tank took car of the engine temps. Water/methanol injection keeps my EGT below 850° when programmed to my driving habits.

Awesome. Thanks for all the info

I ordered a new aluminum radiator with a 2.5" thick core, which was the thickest I could find. My current radiator core is only 1.75". I also ordered the flowkooler high flow pump. I'll hopefully get that all installed next week, and get the truck back out on the highway for some testing.

If it still runs hot I'll call Heath and ask about that fan and clutch. I can't tell when my fan clutch locks up like I can in my mom's 96 k3500, so maybe a better clutch would help if the radiator and pump don't get me where I need. I mostly have problems at highway speed and I don't think the fan will be helpful there, but I bet it helps a lot at lower speeds in the sand and I do sometimes start overheating there too

Water/meth will be the last thing I try, after all the mechanical upgrades and adding some kind of cold air intake. EGT under 900 all the time sounds awesome, 10 gallons of water is just a lot of weight to carry and it's another system to install and maintain. But who am I kidding, I'll probably end up with it at some point

The Heath stuff is reverse rotation serpentine belt. I don’t know of a V belt fan clutch and larger fan.

Barrman said:

The Heath stuff is reverse rotation serpentine belt. I don’t know of a V belt fan clutch and larger fan.

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Ah ok. That explains why I haven't seen one. Thanks again!

I have looked but not found V belt rotation parts that are as good.

Evening. Would it be possible to use the fan and clutch from an M998 basic or A1? Those used v belts.

The stock radiator was the best. You can't get those. I tried the aftermarket brass units, they're junk. Half the weight of stock and they pop randomly. I have an aftermarket aluminum/plastic unit and it's been fine but that's all I can say about it. There are some welded aluminum units out there. Maybe they're better. You aren't making a lot of power so you don't need a lot of radiator. I'd be looking at the fan clutch if your running hot under load.

Barrman said:

I have looked but not found V belt rotation parts that are as good.

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There is an upgraded 7 blade fan available from Summit; Part number OER-3991431, as well as a severe duty fan clutch available from Summit as well. Part number HDA-2799.
Hope this helps.

Thank you for the links. Any idea how to find the lock up percent and duty cycle for that fan clutch? I wasn’t able to.