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Discussion Starter · #1 · (Edited)
OK I read thru the over heat issues but mine is different and I wanted to get everyone's take. Also I have had mine for 5yrs now and do some pretty heavy towing a wakeboat so I know what this truck is capable of if anyone has any other questions on heavy towing with these, I added a huge tranny cooler made for a F350 and magnaflow. Understand that althought the boat weighs 5000-6000 with the waketower and speakers are like a windsail so at 65-75MPH the weight would more feel like 8000lbs with the wind resistance on the engine pulling it.

ok last 4 yrs-- the temp guage never got over 220ish--never under any conditions towing 6000lbs, ac on, hills no issues. This summer it starts to run hot (up to the 3/4 part of the guage, 240's, A/C makes it WAY worse) and I get a check engine light--the code is "Engine Fan Rational" So I end up replacing the fan clutch. FYI they made an EXTREME DUTY fan clutch at least for the 5.3, I got it from an Oreilly's in NC. SPINS MUCH FASTER than the OEM for that first 10 seconds when you start the truck. 209$ then I had a mechanic install for 150$. It did not solve the issue.

Now the problem is when is the computer set to kick the fan up into high gear? It never kicks into high gear up to 240ish, tho hotest it went before I turned the heater on was 240ish. I started freaking out slowed down and turn the heater on and it cooled down some. At what temp should it hit that high revving sound like for the first 10 seconds when you start the truck? That is what I need. I would think anything above 215 it would kick into high gear and cool the engine down to the 210 midpoint. Or is it ok to run it almost all the way up to the red line at 265? Non towing it does fine, a little warmer, maybe up to 225. Do any of those performance programmmers allow you to adjust the settings of when the fan clutches kicks in and off high gear?

At what temp does everyone else's fan kick into the high gear? That high gear on the fan would solve my problems for sure.
 

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2004 chevy trailblazer_ls
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I am not good at problem shooting but if you already changed the fan clutch, it might be your thermostat. I might be getting stuck closed. Thats the only thing i can think of.
 

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Discussion Starter · #3 ·
I dont think it could be that as it is fine when I am not towing-- only really gets hot when I am towing--especailly with the a/c on. Still doesnt explain why the fan doesnt kick up into high gear even if the therm was stuck in closed position.
 

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There really isn't a "high gear" for the fan. It's a smooth and continuous control by way of a PWM signal. I was towing my 3500 pound trailer last weekend from sea level up to 6000 feet, in 103 degree ambient for part of the way, and watching the entire time with scan software. What the PCM does is command a fan RPM, and monitor the resulting RPM, and if they have a significant mismatch for long enough time, it will throw a code.

On a flat road, with 40-60 MPH airflow over the radiator, the fan isn't going to help much, so the commanded fan RPM might be as low as 500-800 RPM. Going uphill in 2nd gear, 4500 engine RPM, 40-50 MPH ground speed, the commanded fan RPM got as high as 1700 RPM, with ECT of 225 degrees or so. In severe overheating conditions, with almost no ground speed in offroad hillclimbs in the desert, I might have seen commanded fan RPM of 2400 RPM.

I would never run it past 240, certainly never to redline.

If you have access to a scan tool or software to monitor the parameters, you might learn some things about what your commanded fan RPM is while it's overheating. But I would guess the thermostat is the first thing to try. Except for the annoyance of moving the alternator, the part is cheap, like $30. Just swap it.
 

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Discussion Starter · #6 · (Edited)
Fan Clutch/ ECT Sensor / or computer--FLEXALITE 292

Yeah I got you. I think mine might be a little different though as I am regularly towing 5000+lbs in 95+ degree temps and I want to do it with the A/C on at 65+mph. And again, my 5000+lbs prob feels like 6-8000lbs with the waketower and other stuff acting like a windsail. Also I had a big tranny cooler installed, one for a F350 so it is pretty big and that sits in front off to the side of the radiator blocking some of that airflow that. its like 14" x 10 or so.

Also my A/C works great-- I mean real good. Ice cold ALL the time. So means that condensor up front is hot as hell adding to the problem. But none of this explains why the computer or whatever never kicks the fan into high RPMs for anything over 210 or so. I think that is a programming fault for all our trucks. Anything over 215ish and our trucks should sounds like a turbo prop untill they cool under 210.


Well I just popped for the Flexalite 292 electric twin fan and should have that installed here in a few days. I am not willing to sit around with the dealership and play games flushing the system again, diagnostics, and still have no results and stupid looks out 300-500$. Cost was 500$ shipped and I am paying a mechanic 300$ to remove the fan and fan clutch and install it. It hits 4600 cfm -- they said the OEM produces maybe 2000CFM MAX. It also has an adjustable thermostat, 60%-100% power in 10 degrees-- So I will set it at 205ish where it will be at 60% power and will hit 100% power 10deg later at 215 or so if it needs it. Its a quick adjustment with an allen wrench. I will let you guys know how it works. This last weekend-- No towing, 90deg, w/ a/c on in stop and go traffic I was hitting 225. Complete BS for the fan not to hit high gear.
 

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I would have been fascinated to see some PCM data before and after. I think throwing a solution like this on a situation where you don't have good detailed scan data is not going to be as satisfying as you think. I agree there's no reason for you to get an ECT of 225 under those conditions if everything's working OK, but I wouldn't blame the fan first. For less than you're spending you could get a scan tool or software and take a look at the actual fan RPM and see if it's commanded to go to a decent percentage of engine RPM.

And without the OEM fan clutch or a controller that fools the PCM, you're going to get codes thrown that you'll have to be clearing all the time to make sure that OTHER error codes aren't turning on the SES light.

Here's some screenshots of data I saved from some hot hillclimbs. First is with OEM fan, and the second was when I was evaluating the PCMforless LS1 fan controller. I allowed it to overheat to prove the LS1 fan/shroud combination didn't have enough airflow in the I6 situation to be a good alternative.
 

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Discussion Starter · #8 ·
Ya I got what you are saying but I dont follow. Sure I could buy a scan or tunner for 500$ to see that my engine is getting hot and the fan is turning slow. That doesnt solve the problem. I dont have any error codes and the mechanic assured me they have done several of these and Flexalite has that part covered with their exact fits, ours is their 292. So I have my fingers crossed on that. But I would rather have an error code because of an add-on than a 240+ degree engine.

Regardless if the computer is telling it to go slow or not, it doesnt solve the problem. Throw 5000lbs+ behind yours in 95deg+, hit some hills or traffic and yours will likely do the same, with the fan spinning slow. So 500$ then another $300 in diagnostics and a PCM reprogram to probrably get the same results? That doesnt even get into the actual repair.

Lots of folks on here are talking about their engines getting 220 or higher and the stock fans, radiator or whatever dont keep up. I think its our computer not programmed right--to kick into high RPM when the temps get high.

$750 DOUBLES my CFM over the radiator GARAUNTEED. As soon as I get in installed and back I will do a heavy tow and see how it goes.

Joke will be on me if I get the same or worse results!
 

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Good luck. We'll be fascinated with the results. I wish I knew the custom code to get a Scangauge II to read out the fan RPM but I don't yet. Need more experimentation. But for under $200, you might consider getting one anyway just to monitor the tranny temp and get a better idea what the TRUE ECT is as seen by the sensor. The gauge has been been proven to be optimistic because the data's filtered by the PCM before being sent to the gauge.
 

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Nyran2001,
Did you ever solve your issue? I am having the exact same problem.

I’ve had my ‘02 Trailblazer for about 5 years and have never had the temp go above 210. I do not tow much, but do live in Texas and the gauge has been very steady up until now.

All of a sudden about a month ago the temp gauge started climbing to 240, almost to 260. Went ahead myself replaced the thermostat and the water pump, figuring it had to be one of those. That still didn’t solve the problem, so took it to the local mechanic and they replaced the fan clutch and updated the PCM.

It is still overheating after about 15-20min of in town driving. When it is overheating, turning off the AC makes the temp go down a little. Turning the heater on full, cools it down significantly. There are no engine light or codes.

So my guess is down to two different things: the radiator may have some corrosion in it preventing max cooling, or could be a head gasket problem. Any other ideas?
 

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Is it me or are there suddenly quite a few members have cooling issues, where they've replaced the clutch, pump and stat and still have heat issues?

Are you sure the temps are that high and not a problem with a sensor? (Sensors fail commonly across many brands and models from time to time).

If not, the next round of things to check in my book would be the hoses, particularly the suction hose to be sure it hasn't become soft and compressing. After that, we're looking towards the radiator itself, possibly there's a breakdown over time of the Dexcool or improperly maintained systems and the radiator is partially clogged? About the only thing that leaves would be an issue at/in the motor, head gasket or something common going on between all those affected. (This is starting to look bizzare). Not isolated to just '02, '03, but involving later years as well......the head gaskets were modified in '03 or '04, so that rules out that common denominator.
 

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Discussion Starter · #12 ·
I think so. Now I ended up using the flexalite 410. Smaller and less CFM. The 292 would fit the radiator but then you couldnt get the computer to fit back into place. Waiting for a really hot day to see what it does.

So far the 410 works great, never gets above 205ish. And holy CRAP the A/C is cold as hell within seconds!!!!
 

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Discussion Starter · #13 ·
Yep lots of folks are having cooling issues.

OK even if my therostat, fan clutch, bla bla bla all of it went bad all at once, WHY DOESNT MY FAN KICK INTO HIGH GEAR WHEN ITS HITTING 230?

I replaced all that crap and it still went hot. Flawed system, no one could explain. That is a computer programing problem. Engine hot should = Fan high gear. Doesnt.

so far the flexalite 410 works great, but I need to tow my 5000lb boat on a hot day up hill with the A/C on to verify.
 
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