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Discussion Starter #1
Hi all! I posted this in another thread a couple days ago but it did not get the responces I had hoped for,...so I started a new thread. Sorry if I'm asking questions that have already been answered here. Since most of the questions concerning over heating when towing are asked from people who live in cooler climates I think my questions here are valid, so please allow me.

I was pulling my '20 ski boat yesterday through the valley here in Arizona. Not sure what the boat weighs but I'm guessing about 3600 pounds including trailer. Temp outside was ~107 degrees and I did have the air on. I pulled it up and down a few hills (not more than 2 miles long each) and across straight flat highway a total of ~75 miles. The temp stayed right around 210 for most of the trip. About 10 miles from home, taking off from a traffic light I got down on it a little hard to keep up with traffic. The temp climbed to about 225 or so and stayed there almost until I got home.

This is an '03 TB LXT with 5.3 and 70K miles.

I recently did a complete coolant flush using a mixture of vinegar and distilled water to flush with. I then did 4 rinse cycles using 100% distilled water (driving vehicle between each rinse). I finally refilled the system with a mixture of 1.5 gallons of "Peak Long Life -mix w/anything", one bottle of Water Wetter and the rest distilled water. My thermostat was replaced last fall and so was my fan clutch and belt. I believe my cooling system is in good condition,... or I did so until reading this thread.

Is it possible with the high ambient temp, towing and the fact that I put the hammer down a little that I've just reach the max capacity of my cooling system? Or do you guys think I too have a problem? A question about fan clutches,....Is the stock GM one the best to buy or is there an aftermarket one that's better? Isn't the fan speed monitored by the ECM/PCM? If so,...how much under speed would set a code? Has anyone tried using an extra electric pusher fan in front on their radiator? Would this impede airflow across the radiator at highway speeds? If I have reached the capacity of my cooling system is there an aftermarket heavy duty radiator available for these vehicles? Mine did come from the factory with the towing package.

I know I don't have sludge in my radiator. I've flushed it very thoroughly as I've indicated here. I've also checked for this many times. Is sludge the only issue with mixing coolants? Reading the literature on the jug of Dex-cool indicates that it is ethylene-glycol based just like most of the "green" stuff. The additives and corrosion inhibitors are what's different,....so why would it be any better of a coolant?

One final question,...is my cooling system the reverse flow type? This would stand to reason since the thermostat housing connects directly to the lower radiator hose.

Sorry for this being so long winded. Just trying to grasp an understanding of all of this. Many thanks to all who reply!
 

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Couple of thoughts...

First, are you towing in OD? If so, shift to 3 instead. In OD, you are forcing the engine to put out 30% more power to compensate for the 30% overdrive in the transmission. Doing that alone should help. Don't worry about over-revving the engine, getting it up into the power band will actually help instead of hurt performance and mileage and temps should decrease also.

Second, are you running an auxillary transmission cooler? If not, get one -- now. Your transmission is heating up, which is causing the engine temps to rise as the radiator is doing additional work to cool the hot transmission fluid flowing through the factory cooler. Add a plate-type cooler to the factory cooler (in series) to help it.

Third, our fans can move a ton of air, so I doubt that air flow across the radiator is the culprit. You have also done your homework with the cooling system, so it is probably at capacity. There won't be many gains to be seen there unless you contract for someone to build you a custom radiator with a thicker core.

Fourth, what is your gear ratio? If you have a 3:42 truck, you are REALLY working it (see #1 above). Changing to a 4:10 ratio would help a ton if you intend on continued towing.

Fourth, take your foot out of it a little bit... You are almost doubling the weight of the stock truck with your load. Take it easy. If you work it hard, you should expect it to overheat -- especially in Arizona climate conditions. In Montana you might get away with what you are doing, i.e., " I got down on it a little hard to keep up with traffic..." You may not actually be able to run with traffic pulling that load -- that's the price for towing.
 

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I agree 100% with the "tow in 3" point. You get another benefit from that - the engine RPM is higher, so if the fan speed is commanded to 100% of engine RPM, you'll get more cooling.

107 air temp is pretty extreme. And the temp above the pavement might be even worse. I used EFILive software to monitor my commanded fan RPM a few times in 95 degree ambient low groundspeed hill climbs, and after a few minutes of WOT on 20-25 degree offroad trails in 4LO, the cooling system would saturate and the fan would be at 100% and the coolant would go to 215 or 220. But in 4LO and low forward speed I had no aid from natural airflow through the radiator. Soon as the trail flattened out and I could do 25-30 MPH the temp came right back down within minutes.

The gauge also lies. It filters and massages the true ECT to reassure the driver. If it displayed 225 you might have been even higher. Recommend getting a Scangauge II so you can monitor the ECT *and* the tranny temps in real time with the true data stream from the sensors.

I've never heard of a larger radiator. [The one on the I6 is ALREADY 50% larger than the one on the V8!]This was wrong. Retracted.

Other questions: The code that's set for fan under- or over-RPM requires a mismatch of 1000 RPM for more than 100 consecutive seconds.

I can't imagine an electric pusher fan doing anything but impeding airflow when it was turned off. There are many discussions of efans on the site, but one commercialized product for the I6 was withdrawn from the market. Mostly because many owners just can't follow electrical install instructions for the controller module, but also because the efan shroud and fan motors being bought were meant for V8 Camaros, for instance, and that radiator was smaller so the shroud didn't totally cover the I6 radiator. I confirmed it just couldn't keep up with my particular hot offroading conditions.

The OEM fan is made by Behr, but there are aftermarket clones. Some of these cheapies are dogs. Dorman started offering one for aftermarket stores due to the high failure rate of the pre-2005 OEM units, and it's a good price, but early reports are that a percentage are DOA. A pain to remove again and replace even if you get a warranty replacement.

Lots of good reading about theory of operation here:
http://forums.trailvoy.com/showthread.php?t=19604

If the fan clutch works, as they all should, there's no performance issue. It maxes out at 100% of engine RPM, and no vendor can do more than that. If you got scanned by EFILive while running hot, you could confirm you were getting max RPM without slippage. And I strongly suggest getting a tranny cooler and watching the real data with a Scangauge II.

On the flush and coolant replacement - great job! I have no doubt you're getting all the performance you can out of the coolant.

Water pump efficiency might be a minor possible issue, if the impeller is eroding, but I don't seem to recall many reports of aging water pump impellers - just the usual bad bearings, seals, and that sort of obvious stuff.

I tow a 3500 pound trailer, and have seen 225 degrees on long hill climbs in 90+ degrees ambient where I have to go into 2nd gear to do 50-55 MPH. The RPM is very high, with my 3.73 gears. I haven't been towing recently after getting the Scangauge II. But I do have two trailer trips coming up in the next three weeks, both of which are going to involve those hot hill climbs, so I should be able to gather more data for all of us. (Assuming I can get Mrs. Roadie to drive while I run the PC. ;) )
 

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Discussion Starter #4
Thanks Roadie and Fredrick. Lots of good tips here. Yes, I know I should take it easy when towing. I don't "get down on it" very often. On this trip I was towing in third.

I'm not sure what my gear ratio is but tomorrow I will review all my RPO codes and get that determined. I will be ordering a Tru-Cool tranny cooler this weekend. My fan clutch is a Dorman brand from Autozone. So based on what I've read so far on this site,... these units did not get upgraded like the ones supplied by Behr. So I have to wonder if I'm getting all the airflow that I should as I have never heard the fan making much noise, even when ambient temps are >100. If It is determined that I need to replace the clutch I'll probably purchase the Hayden brand from Summit.

About the Scangauge,...is it a stand-alone tool or does it require a laptop to be used with it.

Thanks again for the replies. I will keep you guys posted on the results.
 

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Another thing that you have to consider is if the temp started to climb after you got off the expressway. I find that when I'm towing and I stop for gas or rest stops the temp likes to climb. Obviously less air flowing when at full speed. However, it seems like this is something that you have done before and the temp spike is a new development. I am guessing the culprit is likely a combination of things and the high ambient temp of 107 does not help. We don't see that up north, here. I would get the aux trans cooler and check the fan clutch function.
 

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Discussion Starter #6
Update

Okay, so I ordered the Tru Cool tranny cooler. It came in Friday and I installed it over the weekend. I got the 22,000 GVWR unit,...had to dismantle the whole front-end to install it but it fit, and fit nicely. But now I have discovered that my fan clutch is not working properly. With the A/C on and temp @ ~210 degress I can stop the fan dead still at idle. So I'm pretty sure the clutch is bad. It was replaced ~a year ago but the replacement one was a Dorman unit from Korea (Autozone). I visited Autozone and talked to the manager and they agreed to refund my money (lifetime warranty). I ordered the Hayden #3200 unit to replace the bad Dorman one. Will update this post once new unit is installed. I haven't towed with the tranny cooler installed yet. But have driven 40+ miles in 105+ degree temps. Even with the bad fan clutch and A/C on the coolant temp doesn't show above ~210.
 

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Discussion Starter #7
I know this is a bit late but here's an update to my towing/overheating issue. Towing with the tranny cooler installed didn't seem to make too much difference in coolant temp as apposed to just having the factory cooler. The aftermarket and factory coolers are both functional (after-market in-line first).

I replaced the Dorman fan clutch with the new Hayden unit. At first there was not much difference noticed in coolant temp but my A/C did seem to work better. Remembering that the PCM does not engage the fan clutch at 100% until the coolant temp reaches ~260 (as per the factory service manual) I decided to do a little experimenting. I pulled up the wiring diagram for the fan clutch circuit (from the factory manual) and determined which wire is fed to engage the fan clutch. I then wired in a manually operated toggle switch so to apply current to this circuit. Now it can be driver controlled.

I must mention here that I checked with PCMforless about getting my PCM re-programmed to turn the fan clutch on at a cooler temp. They replied to me that they do not have access to the tables that control this function of the PCM and that they could not re-program our PCMs for this function.

Now for the test: A couple weeks ago I was towing my boat back from Lake Pleasant. It was ~4 PM on a Sunday afternoon and the ambient temp was 106* and I was running in 3rd gear. Most of the trip I had the toggle switch in the OFF position to allow the fan to operate normally. I kept it off 'til my coolant temp reached 220* as read on my ScanGauge*. As soon as the temp read 220* I turned the switch on. Almost immediately I could hear the fan start to roar and within seconds the temp started to drop. It took less than 2 minutes for the temp to be back down to 200*. After that it slowly dropped even more to 195*. That's a 25* difference. I've towed 3 times since the added circuit was installed with similar results. The only problem I've seen so far with this is that it does cause the PCM to set the CEL and store a code for coolant fan over-speed. This is not a problem to me because using the ScanGauge easily clears the code.
 

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Fantastic report! Thanks! I've been meaning to make a PWM controller to do a similar thing, but if connecting straight DC to the fan clutch input works OK (and didn't burn out the receiving circuit) then I'm going to go clip one in. You just applied 12V? With or without a current limiting resistor? I loaned my scope to my son-in-law out of town, so I can't see the real waveform. :confused:
 

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I agree with the roadie, thanks for coming back and reporting more info.

I would strongly suggest changing your trans cooler to be after the factory one, the factory "cooler" is more of a heater and then the aux cooler brings the fluid down in temp. Up to you though.

Interesting to hear about your manual switch, hmmm might have to look into that as well. But my 02 is all but done with its towing duties except light loads for my parents, got the SS to tackle the boats. Maybe efans to free up hp and wire a manual switch into that.

Also, Bill you mentioned that the I6 radiator is 50% larger than the V8s? Really? Where did you find this out, Im really curious about it now.
 

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Also, Bill you mentioned that the I6 radiator is 50% larger than the V8s? Really? Where did you find this out, Im really curious about it now.
And I'm trying to recreate the research I did. Sadly, it wasn't from looking at V8s at a meet. It was from some part number research. Let's see if I can duplicate it, or retract my claim:

From rockauto.com:

SS and V8 radiator:

ACDELCO Part # 21506 {#15196386}
RADIATOR w/4-SPD A/TRANS(M30) or 4-SPD A/TRANS(M70) or A/C FRT AUTO/AUX CONT(CJ2) or A/C FRT MAN/AUX CONTROL(CJ3); CORE SIZE 27IN X 18 1/8IN X 7/8IN, CODE GBE,CAY, TRANS OIL CL
$497.79 $0.00 $497.79

I6:

ACDELCO Part # 21505 {#15196385}
RADIATOR w/4-SPD A/TRANS(M30) or A/C FRT AUTO/AUX CONT(CJ2) or A/C FRT MAN/AUX CONTROL(CJ3); CORE SIZE 27IN X 18 1/8IN X 7/8IN, CODE YEA,CAX, TRANS OIL CLR
$400.79 $0.00 $400.79

Ahhhh. My goof. Was looking at I6 data from Rockauto - compared to an Ebay vendor who said the V8 radiator was 18" for the first dimension, and on my 1024 X 768 tablet monitor, the " X 26.5 X 1 1/8" was scrolled off the screen. Stupid new Ebay display format. I assumed the V8 radiator was 18" X 18" which was insane. Sorry.
 

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I would strongly suggest changing your trans cooler to be after the factory one, the factory "cooler" is more of a heater and then the aux cooler brings the fluid down in temp. Up to you though.

.
Depends on where you live... I do them like he did, so that the radiator can still heat up the transmission when it's cold out, rather than heating up the trans fluid, then cooling it back off in the aftermarket cooler, before heading back to the trans... Works well in the summer, too, because the radiator is rarely over 200F, so it gets it up to 160-180 quicker, but doesn't really hurt anything when the trans is already heated up... If you've got it after the factory cooler, the rad puts a little bit of much-needed heat into the fluid in the winter, then the aux cooler knocks it back down... Delays transmission warm-up a lot more in the winter...

For him, though, living in AZ, I'd suggest switching it, too... No real winter to speak of, and LOTS of HOT DRY summer to worry about...

Mike
 

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Discussion Starter #12
Fantastic report! Thanks! I've been meaning to make a PWM controller to do a similar thing, but if connecting straight DC to the fan clutch input works OK (and didn't burn out the receiving circuit) then I'm going to go clip one in. You just applied 12V? With or without a current limiting resistor? I loaned my scope to my son-in-law out of town, so I can't see the real waveform. :confused:

Yes, just straight 12vdc. I tapped off of the heavy gauge red cable feeding the fuse/relay box under the hood on the driver's side. I put an inline fuse holder and feed the switch with that. Then off the other side of the switch I fed into the white wire going to the fan clutch. The fan clutch is normally feed through a relay which is controlled by the PCM. The fan clutch relay is located in this same fuse/relay box so if you are real anal about adding extra wires under the hood you can make it look really neat if you are willing to dig into that harness to find the white wire. I just went straight to the fan. It was easier that way.
 

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Here's another update of my latest towing experience. I towed my 20' Malibu ski boat to Lake Roosevelt over the weekend. Trip started about noon time on Friday from Maricopa, AZ where I live. It's about 130 mile each way with at least four 7% uphill grades lasting 3+ miles each. The temp was 98*. The boat and my TB were loaded with gear. On everyone of the uphill grades my coolant temp would rise to 220*. That was my limit that I told myself when I'd turn the coolant fan on to 100%. One time without paying close attention I let it get to 225* (Scangauge reading). Within 2-3 seconds of turning the fan switch on I could hear the fan start to whirl and almost immediately the temp would start to fall. It took about 2 minutes and the temp was under 200. This would happen even when still climbing one of the 7% uphill grades.

Before the modification I was strongly considering buying a cowl induction hood to be modified for heat extraction. But now I am much less concerned and feel it not to be needed.
 

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vewy vewy intewesting... You're sure you've got the latest fan calibration??

Mike
 

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I agree it's interesting. I don't recall seeing the fan calibration table in earlier versions of EFI Live, but I just checked my latest update, and it's there.

And the commanded speeds look quite suboptimal. Let me go fiddle with these before going to the desert this weekend and I'll see what happens.
 

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Discussion Starter #18
I agree it's interesting. I don't recall seeing the fan calibration table in earlier versions of EFI Live, but I just checked my latest update, and it's there.

And the commanded speeds look quite suboptimal. Let me go fiddle with these before going to the desert this weekend and I'll see what happens.
My service manual says the fan is commanded on at 100% at ~260 deg. F. 121* C = 242* F. So has the coolant fan table been updated since '03? I don't know if my PCM has ever been updated with new programming. Even if it has been 242 is too high for my comfort zone.
 

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My service manual says the fan is commanded on at 100% at ~260 deg. F. 121* C = 242* F.
The service manual could be right - it just doesn't address the LOWEST temp at which the fan is commanded on 100%.

I agree - I don't like those numbers. I want a cool engine, I don't care about noise, I don't care about losing 2-5 HP. If it's hot, and in the desert it's often hot, I want my airflow! :cool:
 

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Yes, just straight 12vdc. I tapped off of the heavy gauge red cable feeding the fuse/relay box under the hood on the driver's side. I put an inline fuse holder and feed the switch with that. Then off the other side of the switch I fed into the white wire going to the fan clutch. The fan clutch is normally feed through a relay which is controlled by the PCM. The fan clutch relay is located in this same fuse/relay box so if you are real anal about adding extra wires under the hood you can make it look really neat if you are willing to dig into that harness to find the white wire. I just went straight to the fan. It was easier that way.
Would you mind posting a couple photo's of this? Your wiring and where you placed the your switch?
 
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