12three

I have a 2007 Uplander Cargo with a 3.9L motor and 125k miles.
At the beginning of summer my AC leaked. Before I put significant effort into diagnosing and fixing the AC the vehicle started trying to overheat at idle and/or very slow paced driving. When the temp gauge gets to the first hash mark past the center the fan* kicks on and the temp drops back to the center of the gauge in a quick moment. a minute later the temp will creep back up again and the process will repeat itself. is this normal operation on an 85 degree day without the AC on? I currently have water only in the system.

I believe that if my AC worked that it would automatically flip my cooling fans on, but I cannot confirm this since my AC is leaking and probably not worth fixing. I am quite confident that if indeed the AC flips the fans on that I would never see my temp gauge rise... but i dont know if I should be worried about this or not...

I did have some notables: the van currently is running on water only, no dexcool at the moment while I am diagnosing (maybe thats the part of the issue?). in the process of trying to fix the overheating I have thrown a ton of parts and procedures at it... New Delco thermostat and gasket, Delco radiator cap, BWD coolant temp sensor, Gates water pump and gasket, new heater core hoses and quick connect elbows, The system has seen about 3-4 prestone chemical flushes of about 3-5 days and 100 miles each, it has been flushed with the prestone garden hose kit 3-4 times as well. I picked up a no-spill funnel and I believe I have eradicated any potential air gaps with it. The RH fan is seized up but I clipped its wires and removed it from the 'low speed' fan circuit (SERIES), so the LH fan does come on when it gets the signal to come on at both low and high now. the LH fan alone is enough to bring the temp gauge back to the center in a second or two.

There are no obvious leaks, and the system holds pressure.

driving at regular road speeds pushes enough air through the radiator to keep the temp from rising and the radiator fins look unobstructed. based on this I would think the inside of the radiator is unobstructed and otherwise functional. The vehicle does not run poorly and does not display any driving/running symptoms that would indicate a headgasket issue.

So after all the parts and all the time I have thrown at it, the symptom is essentially the same: the temp gauge moves to the first hash mark to the right of the center hash. when it hits this first hash to the right of center it triggers the fan and the temp comes back down. I do not recall the temperatures for each hash off the top of my head, but is this normal behavior? should i just fill it with 50-50 dex and keep an eye on it or do i have a problem still?

oilcanhenry

Are you sure that all of the air is out of the cooling system? Are you losing any water-coolant, even if you dont see a leak?

12three

i am quite certain there is no air. i put the no spill funnel on, watched it take a drink, ran it up to 2500 rpms, made sure i had heat, made sure it went up to full temp for a few mins. shut her down and left the funnel on, watched it take another drink and cool to ambient temp, fired it again, 2500 rpms again, let it cool.

it doesnt leak anything, it holds pressure too

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oilcanhenry

Well, GM designed it to have two fans, not one. I searched for used parts but the one fan alone was $103 USD. Maybe you can find a used one. It may be off a differnent vehicle, as lots of cars use the same parts. Autozone shows a few universal fans that will work, and they are new as well.

https://www.autozone.com/cooling-hea...r-fan-assembly

Just plug the vehicle info into the site and see if that might be of help. As for the anti-freeze, I dont think it will solve your issue, but you do need to add some corrosion inhibitor to your cooling system for sure, if you live where it doesn't get cold.

12three

i have temporarily rectified my broken fan problem by cutting the broken fan out of the series circuit... this forces the lone working fan to run on HIGH even when the ecm tells it to run on low. its sufficient as a stop gap as it does lower the temp quickly and effectively from 225 down to 215 when the ecm clicks it on. the ecm clicks the fan off at 215. if you have one fan that is broken and you dont cut it out of the series circuit NEITHER fan will operate on low speed... your good/working fan wont click on until the ecm tells it to run on the high-speed parallel circuit.

the fans on my 07 3.9L are electronically controlled... if AC is off they do not turn on at all until the coolant temp sensor hits ~225degrees...on my van 225 is the first hash mark right of dead center on the temp gauge. when it hits 225 it runs both fans in series on low speed. i dont precisely remember what temp triggers the fans to run on high speed but i know it is the second hash mark to the right of dead center on the temp gauge. i believe that was 235 but dont quote me on the temp. when the fans get the signal to run on high speed they do so in a parallel circuit...but neither fan comes on before 225 without the ac on, which im thinking is a bit of a design flaw bc when the AC goes out, or the operator enjoys sweating, you apparently need to wire in a fan switch to keep the motor from hitting 225. if your AC system is faulty and it refuses to turn the compressor on then it also refuses to turn the fans on. i assume letting it briefly hit 225 is detrimental, but maybe not? im sure a tuner could probably tell the ecm to run the fans on low at a lower temp but thats probably as much $ as fixing the AC...

12three

spoke to a five chevy service advisors.. found one who wasnt mostly useless and could describe vac-filling correctly. he said vac-fill isnt required but that is how they do it. he said that the temp gauge hitting 225 at low speed or idle is normal so long as fans kick on and bring it back to the middle of the gauge... so i guess my concerns were much-ado about nothing unless someone here chimes in and claims their temp gauge is always dead center with ac off even at 85 degrees outside ambient temps

oilcanhenry

Yeah your Uplander can take 225 PSI, but that's with the pressure cap as water boils at 210-212F as you know. I'd sure put some corrosion inhibitor in there however.

12three

i dunno 225 seems high to me but i dont see what i can do until i take a stab at the AC.. almost all of the wires, conduits, and plastic electrical connectors on or very near the motor have just crumpled, i assume due to excess heat. the knock sensors, coolant temp sensor, crank position sensor, and all their wires and conduits.. just to name a few.

i think the prestone chemical flushes did ok against corrosion. i was going to say they did terrible but i just remembered that when i was catching the contents coming from the radiator drain plug that it was drizzling down the rusty radiator support and some of the crap in the water was probably from the rusty support. either way, shes filled back up with dexcool now. dumped a bottle of the lucas super coolant in too. lucas products havent burned me yet... i think i gave like $2 for the bottle, so no complaints there

12three

here is an update:
i replaced the fans, the radiator, a few hoses, etc since my last post. the vehicle still goes up to 225 degrees before the fans come on.
my next best guesses are the belt and then the tensioner... maybe the belt stretched and isnt turning the water pump at full blast, i dunno. i have heard belt and tensioner should be replaced together but i plan to do the belt first and see what happens since the new tensioner is a bit pricey for a tensioner...

i diagnosed the AC... holes in condenser. i plan a condenser replacement before it gets warm this spring.

lastly after looking at many junkyard 3.9l uplander, montana, terraza, relay vans at yards i concluded that a massive cooling part problem is easily rectified:
the heater hoses are hard to find and one hose is impossible to correctly route with flexhose... i have not seen a single junkyard van have molded hoses. there was a crimp connection on them from the factory. all of my replication attempts leaked a bit or kinked, and most junkyard attempts i saw were probably too high and leaky too... either way, here is the fix:
on the heater core, the lower hose can be routed with enough flex hose and a 90degree quick connect. the higher hose on the heater core requires a molded hose... you wont find one for a 3.9l but you can find one for a 3.5l... the difference, and reason the parts catalogues say it wont fit, is because the 90deg quick connect end of the elbow is too big...buy the molded hose and rip the hose off the elbow then buy the correct 90 degree quick connect elbow and connect your molded hose to the correct 90 degree quick connect elbow WITH A HIGH QUALITY CLAMP OR CRIMP... think oetiker clamps off volvos or pex clamps from home depot... the factory parts are all using special crimps in this location... i dont know why but i assume it is because the molded hose has a ton of bends and it also reduces in size... its sort of wild but one end of the hose is smaller than the other... i can provide part numbers if needed. i used the gates hose and delco elbows