I'm having trouble keeping the water temps down in my '95 K2500. I've installed the HD fan clutch from Heath Diesel, but it still warms up. At idle with the A/C off, it was at just under 210 this weekend (about 93 deg. F outside). As I unhooked the gooseneck trailer, it got up to about 215 or so just at idle. As soon as I unhooked, I took it for a drive up the road and it cooled down to normal temp. I had the radiator flushed and have put about 15,000 miles on it, but it's done this for two years the same way.

I'm probably going to hear about the '97+ cooling mods, but I can't help but think this engine would maintain a normal temp under no load at idle, even without this upgrade. I would hope to be able to run the A/C at idle, but I can't even do that without it heating up.

Towing a 35' gooseneck at about 6000 lbs. empty made it stay just below 210 with the a/c off.

I did boil out my windshield washer fluid, too. Never saw that before.

SnowDrift

Others will undoubtedly chime in here . . . but yes, it is my understanding the the '97 cooling mods will help. Also, from what I've gleaned here and there, it's a good idea to 'flush' the radiator - as in flush all the bugs and debris from between the cooling fins. As I understand it, you can remove the upper radiator core supports and get enough room to do so. Take a look in the 6.5 FAQ, or Do It Yourself area, I believe there is a good description/photo essay f the process.

What thermostat are you running ?

I ran mine this weekend, in like outside air temps, with the A/C on and never got above 190* - on the road empty and at idle, and I do not yet have the cooling mods - pump or fan.

Even with a 95, you should not have problems cooling at IDLE! Something seems odd here.

First off, edit your signature so we can see what you've got....you'll get better answers if we have better info;) . Cleaning the radiator is a good start, but something is definitely wrong if you're over heating at idle. Replacing your thermostat would be a good start (might be stuck closed). You may want to order a dmax 9 blade fan from teamchev.com (around $50) for help cooling at idle. However, stock fan should not let you get up to 210.

I just went through dealing with an overheating problem on my suburban. Turns out that the guy who repaired it put a v-belt clutch and fan blade on it....blades were pitched the wrong way!!! Probably not your problem though.

Start with the thermostat and update your sig. good luck:grd:

Not a good sign when you heat up at idle and puke out coolant. I think you have a cracked head or bad head gaskets. You can probably baby it and drive it awhile longer but get ready to check the reservior regularly to let the air out.

Hi fellas,
I'm a new member with the same problem. I just finished installing the '97 cooling mods on my '93 3500 Dually, and it did not help. The mods are the dual thermostat housing w/180DF thermostats, High output water pump, 9 blade Duramax fan w/15DF cooler than stock fan clutch. It will idle all day with the AC on at 180DF, but take her down the highway, and it heats up to 220DF. I guess my next item is a new radiator. Any recommendations, or recommended vendors that would carry an oversized radiator?

DDEEC,

Clean between your radiator and condensor first.

Not a good sign when you heat up at idle and puke out coolant. I think it's da blue stuff, not the antifreeze.

Ahh, but this does bring back memories from years ago. Way back before being very confidient in workin' under the hood. I had the local shop change the antifreeze in the radiator. More money than brains in my single days it was. . . I remember it well. . . bitz and pieces maybe . . .

Anywho, they only had their brand of ethylene-glycol based coolant. I perfered the proplyene-glycol coolant, so I supplied it and they filled it. As best as I could figure, they filled it full strength. I noticed my washer fluid bubbling out the washer jets, and thought it was unusual. I was hot, but not that hot I thought.

Any idea what concentration your coolant/water mix is?

Thanks QM! I will check that before I dish out $350 -$500 for a new radiator.

I just bought two of them at $100 usd cash each.

I just bought two of them at $100 usd cash each.
That is a steal. When I smashed up the front of my truck:mad: I think the replacement cost for the radiator was $700 iirc-:t

QM,
The windshield washer fluid boiled over, not the coolant. So you mean you bought radiators for $100 each? If so, please let us know where.

knkreb,
It's about 50/50 with an OEM t-stat that was new at the flush 15,000 miles ago.

I'm planning to remove the upper fan shroud and flush the radiator's fins from the back side, hoping there is sand and debris in the fins not allowing it to cool. I guess if this doesn't work, I'll be looking at another good flush out of the truck, or another radiator.

Sorry about the signature, guys. I couldn't figure out how to edit it when I was told to do so a while back. My apologies.

SnowDrift

I'd double check that sending unit and gauge just to make sure it's still reading correctly. Check your fan clutch and clean out the bug stuffings in between those cooling fins. I just installed the first half of the cooling upgrade and so far loving the results. My truck use to run around 200-210 with A/C on and running bout 70 MPH but never at idle?

OH BTW QM where you find those Raditors at that price?

I went to a shop in houston,tx called jose's radiator that could core my old one but one look at the old unit and the guy says buy a new one and that was his price, the other quotes I recieved that day were $270 delivered, and $230 pick-up, so at $100 I bought two.

I did mean the coolant reservior, I'm not sure how the windsheild washer fluid would boil over?

I had a Aerostar minivan that acted the same way once. Ran hot on idle, cooled off as the revs came up.

Turned out to be that the impeller blades on the waterpump were completely GONE! :eek: All that was left was a disk with a few nubs of blades.

I dunno if the 6.5 will do the same thing, but I would check coolant flow at idle straight away.

Tim

My 96 did about the same thing. It would heat load the AC till it stopped working. This was with dual stats OEM installed.

The key was the fan/clutch combo. Some may CLAIM lower engage temps, but there's only one that delivers. STEEL 20" blade is also recommended...

I've had several water pumps with steel impellers eaten away over the last few years. Most likely cause: electrolosis in the coolant/cooling system. Dissimilar metals add to the problem. Seems engines with aluminum water pumps and timing covers on cast iron blocks are worse. The older, all cast iron engines/water pumps didn't exhibit the problem. I've checked engine and chassis grounding on all of them and couldn't find a problem. It still points to the coolant becoming acidic and eating away the blades on the impeller.

Most cars came in for "heating at idle and around town, ok on the highway" complaints.

My 96 did about the same thing. It would heat load the AC till it stopped working. This was with dual stats OEM installed.

The key was the fan/clutch combo. Some may CLAIM lower engage temps, but there's only one that delivers. STEEL 20" blade is also recommended...

Hey JK
Does that clutch / fan setup you got fit pre 97 water pumps?

One of my concerns with the '97 cooling upgrade, and there is a good writeup on this in the FAQ section by GMCTD, is that the original t-stat was a dual plate t-stat that would resrict the bypass line as it opened and force the coolant to flow more to the radiator. On the dual t-stat cross-over there is no provsion for this, and for me it did make a difference. Before the upgrade, my truck would only get hot pulling a load, but now it gets hot running empty down the highway. And fast! That's what leads me to believe that my radiator needs to be acidized or replaced with a larger one. I seem to be bypassing more than flowing to radiator, but the upper radiator hose is very hot, so it is flowing to radiator.
Well I'm going to go see if I can clean some bugs out of it like QM suggested.

check the temp drop across the radiator when engine is too hot. If less than 20 deg you need a radiator or pump. If the the heater puts out gobs of heat (at idle), you likely have a good pump.

Well, I just got back from test run. It's better, but it will still get to 220 @ 70mph, it just takes it a little longer now to get there. I pulled the radiator, washed and flushed it, and washed out the AC core and trans cooler real good. While idling it cools right back down to 180.
I was wondering, that 1 inch bypass seems very large. My 6.2L only has a 1/2 inch bypass. Has anybody tried a 1/2 bypass on a 6.5TD?

Sounds as if your rad/AC was plugged preventing air flow. If your rad is plugged inside(calcium) just flushing with water will not work. (lots of personal experience with this) the tubes get plugged and the rad cant transfer the heat. Maybe in the states you can get a good strong acid type cleaner that will do the trick, we used to be able to buy it here in Canada at Canadian Tire, about 15yrs ago. I have not seen it since it was a strong acid and when you were finished flushing you had to add a neutrilizer...boy did it ever clean out a rad. A good sign the rad is partially plugged is slow but a steady climb in engine temps that will drop down once the engine load or veh speed drops.

I've done the radiator flush before myself. It was very interesting that my wallet took a flush too about two weeks later when my water pump took a dump around the shaft seal. Coincidence? Maybe. . .

Check where the tubes attach to the header. If you see white deposits, don't use a harsh flush, it will leak when you're done! Experience talking.

Humm... good point guys, that is likely the reason Canadian Tire does not sell the "strong " two part rad flush anymore, I assumed it was for environmental reasons. I have not tried it but I've heard that Electasol dish washer crystals will clean out a cooling system quite well, at least it does a bang up job on my dishes!

I have tried CLR in an old rad.. let it sit for a day...really did not do anything at all.

Hey JK
Does that clutch / fan setup you got fit pre 97 water pumps?

Yes. There are some older pumps (typically 6.2?) with odd bolt paterns, but they can be drilled and tapped. I had a guy with a supercharged 454 use my clutch also. He redrilled. I'd recommend the HO water pump/dual stat mod for any 6.5 towing or not.

The plastic tank/aluminum core radiators run with Dex cool seem to be perfect internally provided the system is kept up. Block, timing cover, water pump all look nice inside. This is the setup that I'd recommend.

The plastic tank/aluminum core radiators run with Dex cool seem to be perfect internally provided the system is kept up. Block, timing cover, water pump all look nice inside. This is the setup that I'd recommend.

What year did GM introduce the plastic tank/aluminum core radiator? I know my '98 gasser was a Dex-Cool system. My '94 had some head gasket work done about 6 mo before I bought it. Appears that as part of the repairs the radiator may well have been replaced - there is a bright shiney GM sticker poking out from under the upper portion of the fan shroud. Tanks are plastic and the core appears to aluminum. Can't say whether there's Dex or 'regular' coolant in the system now as the over-flow tank is yellowed to the point that no color comes thru (I really suspect that it's straight H2O !)

I'm thinking dexcool started in '96. If your system is flushed you can run dexcool in it, but not if residue from previous coolants is in the system or it will ruin the dexcool.

Can you go backward/forward from/to Dexacool? I thought I was going a step forward with my old 94 Cavalier, by changing it over to Dexacool from the green stuff. Funny, I had to add stop leak after the inside of the windshield fogged up from the heater core goin' south. Coinicence. . . maybe?

You don't have to worry about the old coolant ruining your dexcool you have to worry about dexcool ruining your engine!!. Dexcool is highly over-rated and I have personally seen 2 engines (95 grand am & 96 transport) with so much sludge in the water jackets it looked like rusty mud, even the rad caps were covered with this stuff, the grand am had a hole rusted thru into the cylinder and it started from the coolant side!! the car had less than 150,000KMs and was faithly maintained by my neighbour who bought it new. I had heard of rumurs of deathcool, prior to opening up his engine and would never have believed it until I saw it. Needless to say I don't use dexcool. There is a class action suit against GM and Dexcool.
http://www.cwcd.com/CM/MassTorts/MassTorts5.asp
Just do a google search on "dexcool" and you will have enough reading for a week. Like I said I won't use the stuff, green is good!

OK, I did it! I took out the 1" bypass hose to the waterpump, and installed a 1/2" hose. Just like a 6.2L has. I measured the ID of the fittings, w/1" hose fitting the ID was 3/4". With the 1/2" hose fittings, the ID is 3/8". This restriction helped out a lot. The truck wouldn't get over 210F on the highway, and city driving, it stayed around 190F. I believe that I will need a new radiator, because I did see white deposits on some of the core ends while I was flushing it out the other day. So, a new radiator is next on the list, but I will leave the 1/2" bypass hose in.

You can use either type, just don't mix them. In order to change from one to the other, flush completely. That means block drain plug removal. Sometimes, troublesome, but definetely necessary. I have replaced my block drain plugs with petcocks just because...

Ok, here's an update. Yesterday I took my upper fan shroud off at the advice of someone else in order to try to back-flush the radiator (externally). I got a bunch of junk out of it and ended up removing the fan, as well, so I could really get at it with the hose. Gobs of dirt (Arkansas red mud) and bugs flushed out. I can see through the fins almost every place, now. I took it for a drive with the A/C on and idled for about 35-45 minutes at our local fairgrounds (while looking for a place to park) and it stayed well below 210.

I think that I'll take the radiator out soon and flush it better when I have more time. Apparently the water was not dumping off enough heat to the radiator for the fan clutch to sense the warm air moving past it. Fan clutch thought everything was just fine, since it didn't have hot air coming by it.

On a side note in regards to the Dex-Cool. I was at our local dealership the other day and one of the parts guys told me GM is going away from the orange (dex-cool) and is switching to blue stuff. What's the blue stuff, I asked. He said it's the same as the old green stuff, just different color. Probably some other minor variation, as well, but just different enough that no one has to confess to a mistake.

SnowDrift

I flushed my DexCool when I bought my truck. Looked like new. Replaced with gree stufff, but after 2 years i replaced with YELLOW extended life antifreeze. Has anyone heard of it? BTW, backflushed my radiator yesterday; I had sticks in front of the radiator:( .

This is an example of a leaky system where air interfaces with the coolant. Every 6.5 that I have had apart using DexCool looked like new inside...


You don't have to worry about the old coolant ruining your dexcool you have to worry about dexcool ruining your engine!!. Dexcool is highly over-rated and I have personally seen 2 engines (95 grand am & 96 transport) with so much sludge in the water jackets it looked like rusty mud, even the rad caps were covered with this stuff, the grand am had a hole rusted thru into the cylinder and it started from the coolant side!! the car had less than 150,000KMs and was faithly maintained by my neighbour who bought it new. I had heard of rumurs of deathcool, prior to opening up his engine and would never have believed it until I saw it. Needless to say I don't use dexcool. There is a class action suit against GM and Dexcool.
http://www.cwcd.com/CM/MassTorts/MassTorts5.asp
Just do a google search on "dexcool" and you will have enough reading for a week. Like I said I won't use the stuff, green is good!

"This is an example of a leaky system where air interfaces with the coolant. Every 6.5 that I have had apart using DexCool looked like new inside..."


What do you mean "air interface"? I thought it had to do more with reactions between the different metals. I'm sure all you read on the net is not true...and I have not opened up any 6.5's but as in the case of the two engines I mentioned...it was bad.
I have not heard of any trouble with Amsoil, or Toyota long life coolant (or any others for that matter) and I have noticed Dexcool now touts a "new formula" banner on their coolant jugs, so maybe there is a little truth in there somewhere

My .02 cents

Nick

Hello Guys, Since I had come in on this thread with my cooling problems, and mods that I had tried, I just wanted to update the group on what I had found to be the problem. Today, I brought my radiator to a local shop to have a custom 5-tube core radiator built. The owner of the shop said that the 4-tube should be doing a good job of cooling the engine. While I was there watching him, he unsoldered one side tank, and I could see that alot of the tubes looked plugged. Then he hooked it up to a water hose with about 55psi on it and flowed water up through the core and out the open end of the core. To my surprise, the core was about 75% blocked! So, to make the story short, he's going to rod it out and put it back together for $60, and that should be the end of my cooling problems for awhile. Oh, and he did recommend that I flush the engine block by leaving the top rad hose off with the engine running and a water hose filling the rad at the same time.