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6.5 over heating

@TRB said his is a '94, which has several strikes against it from the factory as far as lack of cooling and the overheating that cracks valve seats and blows headgaskets. The small single thermostat crossover pipe, 80 gpm unbalanced water pump, wimpy fan blade, asthmatic GM-4 turbo, reduced airflow through grill/stack just being a few of the bigger ones. I had to deal with them on my '94 AFTER both heads cracked at once!

There are multiple threads on here covering your problem and how best to solve it.

Welcome to TTS.
 
Will L. said:
Remember you already knew you were replacing it as it was toasted- the screw thing is literally the death nail of a fanclutch turning it “on” permanently and will never have a chance at working when the screw is taken out. When a person is already buying a new fan clutch and wants to know that the fan clutch is definitely their problem- or if it goes bad in the middle of no where and you need a trick to get you home this works. Or maybe you know it is bad and have no money for parts for a week or two this works. But you will spend more money in fuel by forcing it on all the time like that. We had a President back then who wasn’t driving up the price of fuel on purpose to teach us to buy electric.

You don’t wanna recommend this until you know where the person is in diagnosis and so forth. He just bought a new clutch by the sounds of it- and maybe it’s a good one- we don’t know yet
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Yeah, it seems that when I mention that test procedure, I forget to also me tion tnat it will destroy that fan clutch.
I was fortunate that I had the old spin on fan clutch from My truck that had already failed and so I used that for the test. I also have the almost brand new spin on fan clutch from Kennedy Diesel and it was a failure right out of the box. It is too bad that the warranty had expired on it before I got a good chance to test it out.
If anyone wants a spin on fan clutch for a test procedure PM me and I will send You one that is already setup and ready to go. Just add Your fan and spin it on. No return is necessary.
I also discovered, after running the test fan clutch for several thousand miles, that gooey waxey stuff sort of splatters and gets on stuff. When I recently pulled the top shroud and fan from My truck, I thought, what in the world has been leaking, poked My finger into the stuff and discovered it was quite goopey. Okay, now I know what that is. 😹😹😹😹 cleaned it up with a little solvent and some B&P cleaner and good to go. No more dirt or dust will collect on that area. 😹😹😹
 
Husker6.5 said:
So, what made your fan clutch lose its silicone filling? Did the shaft seal fail? What brand was it?
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It got three holes drilled through it, then threaded and some machine screws screwed through it to lock it up solid.
That little test proved that it was the fan clutches that was causing the engine to over heat.
Then, being that I used no sealant under the screw heads or on the threads, the goop leaked on out. 😹
 
Oh, it was your "screwed up" one that you experimented on, not a new one. My bad, I misunderstood and thought you were talking about the new one you replaced the "experimental screw job" one with, after verifying it was a bad clutch, that you had ran for a while and then found it had barfed its guts out all over everything.
 
Husker6.5 said:
@TRB said his is a '94, which has several strikes against it from the factory as far as lack of cooling and the overheating that cracks valve seats and blows headgaskets. The small single thermostat crossover pipe, 80 gpm unbalanced water pump, wimpy fan blade, asthmatic GM-4 turbo, reduced airflow through grill/stack just being a few of the bigger ones. I had to deal with them on my '94 AFTER both heads cracked at once!

There are multiple threads on here covering your problem and how best to solve it.

Welcome to TTS.
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Believe me, we’ve done all the cooling mods on my son’s ‘94 and it still runs hotter than my ‘99. Must be the oil spray on the pistons in the ‘99. Not convinced the the single thermostat crossover is all that, because the dual did wonders on the old, wrecked ‘95.
 
There were two variations of the single stat crossover. The 94-95 that ran a small diameter thermostat in them and the very rare transitional production 96 large diameter single thermostat in it that was made just before GM came out with the dual thermostat crossover that ran two small diameter thermostats in the housing. Quite a few years back on here there was discussion about the rare large single and iirc a member did some flow testing and found that the single large stat crossover actually outflowed the dual stat crossover that replaced it. Iirc, the large single also incorporated a flow block off that helped the engine warm up to operating temperature faster - and is the basis for the aftermarket kit that's now offered to give the recirculation of the large single stat. I'm sure someone on here will chime in shortly with more details on both the rare large single stat and the dual stat recirculation upgrade.
 
Husker6.5 said:
There were two variations of the single stat crossover. The 94-95 that ran a small diameter thermostat in them and the very rare transitional production 96 large diameter single thermostat in it that was made just before GM came out with the dual thermostat crossover that ran two small diameter thermostats in the housing. Quite a few years back on here there was discussion about the rare large single and iirc a member did some flow testing and found that the single large stat crossover actually outflowed the dual stat crossover that replaced it. Iirc, the large single also incorporated a flow block off that helped the engine warm up to operating temperature faster - and is the basis for the aftermarket kit that's now offered to give the recirculation of the large single stat. I'm sure someone on here will chime in shortly with more details on both the rare large single stat and the dual stat recirculation upgrade.
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My son’s ‘94 has the HO water pump with DMAX Fan and Hayden clutch and Single crossover t-stat housing. That Suburban will have coolant at 190 with an easy mile through the neighborhood at 30 mph. In contrast, my ‘99 with same fan, waterpump and fan clutch will require 15 to 20 miles at highway to get the coolant temp up to 187 where it stays pegged. It’s gotta be the oil spray on the pistons.
 
I finally got the electro/viscous DMAX fan system installed. It was 104 degrees when I took the truck for the first test run over the Yellowstone hill, the engine got up to 195.5 going over the hill on the way out, that was with the AC on max.
Went out several miles and then stepped the speed to about 70 on the return.
It is a long and fairly steep pull on the return of the back side of the Yellowstone hill where it comes up and out of Sunday Creek. Pulling that hill the temp gauge hung about 198 until got over the top. It then finally went to 201.5 and that is the coolest it has ever run onna pull like that.
Last summer the temp gauge would have been up to 210 IIRC.
I am totally impressed with this system.
 
Go re-read my post. Your son's 94 has the small diameter single stat crossover that doesn't flow well with the 80 GPM pump, let alone with the HO 130 GPM pump which that crossover chokes down. The good flowing single crossover was the limited run, RARE, LARGE diameter t-stat crossover that was produced in '96 just before the dual stat crossover came out in production. That is the one that actually out flows the dual stat crossover.

Put a 97+ dual stat crossover on your son's 94 with the HO waterpump and it will perform much better and cool almost as well as your 99 does.
 
Husker6.5 said:
Go re-read my post. Your son's 94 has the small diameter single stat crossover that doesn't flow well with the 80 GPM pump, let alone with the HO 130 GPM pump which that crossover chokes down. The good flowing single crossover was the limited run, RARE, LARGE diameter t-stat crossover that was produced in '96 just before the dual stat crossover came out in production. That is the one that actually out flows the dual stat crossover.

Put a 97+ dual stat crossover on your son's 94 with the HO waterpump and it will perform much better and cool almost as well as your 99 does.
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How does one tell which single crossover they have? mine a 95 had the single but unsure which one. I have noticed that my temp will climb just a tad while on the open road and then go back down as soon as I slow down. I'm sure I have the smaller one! I would like to know what to look for and start scowering fleabay or other places just to see if I can score one :D
 
You have to use the build date code, as some "96s" were built in late 95 and use the small t-stat crossover and some actually built in early 96s used leftover 95 small single t-stat crossovers until the VERY rare large single t-stat transitional production came out for a month or so before the dual t-stat crossover was introduced. There were only a few thousand, at most, of the 96s with the large single t-stat crossovers built. Now, how many wound up in a salvage yard and disappeared forever when the truck/burb was crushed, how very, very few had an owner who knew what that crossover was and salvaged it before either repowering their dead 6.5 with another 6.5 and reused it, or sold it when repowering it with a gasser, and how many very, very few of the large stat 96s are still on the road?
 
dbrannon79 said:
How does one tell which single crossover they have? mine a 95 had the single but unsure which one. I have noticed that my temp will climb just a tad while on the open road and then go back down as soon as I slow down. I'm sure I have the smaller one! I would like to know what to look for and start scowering fleabay or other places just to see if I can score one :D
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You can tell visually by the P/N, or by pulling off the t-stat outlet housing and measuring the diameter of the "lip" the t-stat sits in. It will be, iirc, about ½"-⅝" larger in diameter than the 94-95 single t-stat's. The single large t-stat crossover is so rare that even @RockAutoLLC doesn't list the gasket, t-stat or housing for that crossover in 96, only the 94-95 single and the dual t-stat crossover for 96.
 
Here's a thread with the p/n for the rare single 96 stat

DB2 Conversion questions

Hi guys, a few weeks ago I had posted about my DS4 on the way out. Well it finally bit the dust to the point of not being able to drive it. Following some much needed peer pressure from the responses, I am going the DB2 conversion route. I have started ordering all the parts needed for the job...
www.thetruckstop.us

@dbrannon79 you most likely have the single stat block off style- if the hose connects to the housing facing forward, it's the single stat for 92-95

the rare housing looks like the 96/97+ dual stat with the outlet pointing back to the cab with the wraparound hose

I have the dual stat on my 95, but will be going back to the single stat once I convert to DB2. The IP is much more accessible with the single stat and an aftermarket upper intake. Anyone switching to DB2 with the 97+ dual stat has to fab their own throttle and cruise bracket or modify an existing bracket to clear the dual stat outlet neck
 
TRB, if you are not afraid to tweak things yourself, the FIRST thing I would do is remove your new fan clutch. Look at the tab on the bi-metal spring where it anchors into the aluminum housing. It will be 1/4-5/16" long. Straighten the tab out and bend a new one that is about 1/8" of an inch shorter than the original, and then press the tab back into the housing. Use rtv silicone to hold it it place if it had some originally. Less tension on the bi-metal spring means the valve to engage the clutch will move at a lower temp.

x2 on removing the electric fan

If you don't mind a LOT of engine noise, remove ALL of the insulation/sound deadening material from the engine bay- let that heat out!

Good luck.
 
Big T said:
I want the unicorn crossover!
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Look up the two aftermarket bypassing thermostats in cubical housings I posted. It will be expensive, but then you could have massive flow. In the end, you need to look at how much can the t stat flow when open. I tried to search it to reference it here, but can’t remember right now which thread it was in, or the manufacturer name.
 
Good morning all
here is where I am on the overheating
Drilled hole and locked up fan clutch
drove up the mtn where I normally got up to
200 to 210 with out a load temp ran 185 to 195 all the way up
this is a hard pull lots of curves and straight up egt runs 1100 to 1200
all the way did not have time to pull my camper will do that soon
and let you know
is there any danger in running it with the clutch locked up
would like to leave it that way till I get new pump and elect clutch
can anyone tell me the best place to get pump clutch and steel fan
I will have to replace all sense I have the old style with the 4 bolt fan
also with the elect clutch is it on or off only or is there a way to set
the % of fan

thanks again all for the help
not seen it run this cool sense I got it
 
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