96 GMC K2500 Suburban Restoration (with a couple of mods)

fancyTBI said:

Air compressor with a big wand attachment works well to blow the cooling stack out. I’ve also made an attachment to a garden hose to clean it out. Hose thread to NPT adapter, 2ft of 1/4” PVC, then a modified 90° elbow that I heated and “crushed” the outlet so it was more of a flat piece that would fan the water out a bit. You’d be surprised at the mud and crud that comes out of a clean radiator.

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OK, I was thrown by the term "cooling stack." So I looked it up. It's the entirety of the cooling fins. Doh!

Makes sense now. Thanks.

Yesterday I verified that the auxiliary fan does work. Not sure at what point it comes on, since it's pretty quiet.

When I returned home from a 25 mile round trip (no interstate), the coolant temp was just below 200º F. I parked and let it idle, and sure enough, the fan was spinning. It turned off once I turned the ignition off, which I suppose is intended to keep the battery from running down.

Anyway, between that and having a newish radiator, I'm relieved. Now to do a drain and flush, put in the new thermostat, and give the cooling stack a good blast of compressed air, even though it looks clean. After that, I don't think there will be anything else to be done on the cooling system.

South VA said:

Sorry, it's best to consider me a noob when it comes to anything to do with a cooling system much beyond replacing a thermostat.

I'm trying to envision where to run the compressed air... Through the block drains, hose outlets, radiator neck?

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You figured it out in another post, but you are correct. Through the rad, condenser, PS cooler, trans cooler. Turn your regulator down so you don’t fold over any fins. You can also pressure wash the radiator but I wouldn’t do that while its in the truck; too easy to get a bad angle and really wreak some havoc.

After one more pass through the PO's receipts, I managed to find one for the new radiator. How I missed it is beyond me. Ah well.

The radiator, radiator cap, and the upper and lower hoses were replaced, so those items should be good for awhile. No mention of a thermostat, however. So my purchasing a new one wasn't in vain. Also no mention of a coolant flush. No problem.

Speaking of temperatures, I perused the GM SM a bit further regarding transmission fluid temperature (see below). If I'm reading this correctly, the normal operating range for TFT in the 4L80e appears to be 90º C to 115º C, or 194º F to 239º F.

This squares with Trent's suggestion that above 230º F is a good place to start getting concerned. It could be that he's being a bit conservative, which seems like a good thing.

Again, I'm looking forward to seeing what the temps are when we tow our camper to the mountains on July 8. My guess is that it will be fine.




Oh, and speaking of receipts, I also found one from the end of last October, nearly a year after I purchased the Subdivision, for the reflashed VCM (aka ECU) that I found on eBay. It was the third or fourth one I'd tried, and it was the one that finally worked. I still marvel at how replacing this one component solved the transmission shifting issues that I'd struggled with for months; the intractability of which were beginning to make me question my sanity for continuing to put money into this beast.

I am so thankful that that particular phase of this journey is now in the rear view mirror.

Heading out this morning to Grayson Highlands State Park, near Mouth of Wilson, Virginia. It's just down the road from Mt. Rogers, the highest point in Virginia at 5,278' elevation. This will be our second attempt to get to this park. Last year we had to turn back halfway there, due to what turned out to be a combination of factors leading to transmission shifting issues.

Here in the flatlands it's supposed to reach the low 90s today, a bit cooler than it's been for the past week. It will be interesting to see how the transmission fares, temperature-wise. In the park, however, temps have been running 10 or 15 degrees cooler. Very much looking forward to getting out of this heat.

I'd really like to be able to say that the cooling system has been flushed, and that the new fan is installed. However, they have not. So it looks like this trip will serve as a baseline for trans and coolant temps for summertime towing. I'll be closely monitoring both via the DashCommand app on my phone.

At least the new trailer brake controller is installed. I haven't yet tested it with the trailer hooked up, but the manual says to drive the vehicle without the trailer attached for 10 to 20 miles so that it can self calibrate. Apparently the sensors need to learn the orientation of the unit so that it can proportionately apply the trailer brakes when the vehicle brakes are applied. Interesting.

There's a lot left to do before we get rolling. Good thing I have a pretty decent set of checklists.

South VA said:

new trailer brake controller is installed. I haven't yet tested it with the trailer hooked up, but the manual says to drive the vehicle without the trailer attached for 10 to 20 miles so that it can self calibrate. Apparently the sensors need to learn the orientation of the unit so that it can proportionately apply the trailer brakes when the vehicle brakes are applied. Interesting.

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I'm curious how well it (redarc elite model) works and your opinion of it. I've got the red boxed liberty model to install this week before picking up an equipment trailer.

Hope the trip is a painless enjoyable ride. Pretty area down there. If you want an easy way to see the atmospheric pressure difference, take a sealed bag of chips from the valley up onto Mt. Rogers and note how 'full' it appears at elevation.

termite said:

I'm curious how well it (redarc elite model) works and your opinion of it. I've got the red boxed liberty model to install this week before picking up an equipment trailer.

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The Redarc worked well, once I got it dialed in. The initial setting of 5, recommended in the manual, was a bit too low, so I tried various settings and found 7 to be just about right. And it's nice not having to reach down by my knee to adjust it or to activate the trailer brakes independently.

You may notice the void in the dash where I removed the factory radio, and have yet to install the aftermarket head unit. I really should do something about that.

termite said:

Hope the trip is a painless enjoyable ride. Pretty area down there. If you want an easy way to see the atmospheric pressure difference, take a sealed bag of chips from the valley up onto Mt. Rogers and note how 'full' it appears at elevation.

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Thanks. It is s a beautiful area. Getting to it is a bear, though, particularly through the last stretch of Hwy 58, and then the road into the park. It's pretty steep, and there is a three mile section of 15 mph curves that are just about at the limit (at least in my experience) of towing a 24' camper with a 19' vehicle. Fortunately we didn't meet any large vehicles coming the other way through that stretch.

And yes, we had some pretty well-inflated snack bags when we got to the campground, which I believe is a little over 4000' elevation. We did a fair amount of hiking; the altitude was definitely a factor.

The Subdivision did its job, but had to really work hard over those last few miles. The coolant temp got up to 245º, and the transmission temperature got up to 254º. There was nowhere to pull off and let it cool, so we just kept going to the campground. The temps started dropping as soon as we crested the last hill.

I was afraid I had cooked the transmission, but I looked at and sniffed the transmission fluid, and it was still nice and pink and didn't smell burnt. Plus, after reading the GM Service Manual, was relieved to find that it doesn't generate a code until the temp reaches 277º. Just to be sure, I checked it this morning with my scan tool, and found no codes.

Except for the above, the TFT stayed mostly around 212º, and coolant stayed between 200º and 220º. So now I have baseline values, and what I hope are maximum temperatures for coolant and transmission, under normal and adverse towing conditions at around 85º air temp.

Now to install the new fan and clutch, blow some compressed air through the cooling stack (once my compressor is fixed), and do a drain and flush of the cooling system.
Our next trip is on July 29, to Douthat State Park, and I'd like to have all that done before the trip. We shall see.

South VA said:

The Redarc worked well, once I got it dialed in. The initial setting of 5, recommended in the manual, was a bit too low, so I tried various settings and found 7 to be just about right.

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Glad it worked well. May need to check adjustment of your TT brakes. Trailer brakes generally get neglected by most folks.

South VA said:

The coolant temp got up to 245º, and the transmission temperature got up to 254º. There was nowhere to pull off and let it cool, so we just kept going to the campground. The temps started dropping as soon as we crested the last hill.

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I'd have been getting a little on the nervous side with those water temps. Were you lugging the engine in too high a gear.

South VA said:

Douthat State Park

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Been there, over 20 years ago, maybe longer. I was little at the time. Did hike there a few years ago when I was down there for work overnight. Found a nest of yellowjackets in the ground...good time.

termite said:

Glad it worked well. May need to check adjustment of your TT brakes. Trailer brakes generally get neglected by most folks.

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Thanks. All four brakes, backing plates, and wheel bearings were replaced about a month ago, and are supposed to be self-adjusting. As far as I can tell, everything brake-wise is working as it should.

termite said:

I'd have been getting a little on the nervous side with those water temps. Were you lugging the engine in too high a gear.

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I sure was nervous. That's the highest the water temperature has been in this vehicle. Fortunately it didn't stay that hot for long. I was mostly in 2nd gear. Probably should have gone down to 1st. Next time I'll try that.

termite said:

Been there, over 20 years ago, maybe longer. I was little at the time. Did hike there a few years ago when I was down there for work overnight. Found a nest of yellowjackets in the ground...good time.

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Nothing like a nest of yellowjackets to make for an interesting day!

As posted in another thread, my attempt to install the new fan and clutch was thwarted by a 12mm nut that some ‘mechanic’ substituted for one of the ½“ nuts on the fan mount hub. I'm guessing that whoever did it cranked the nut down with a wrench and cheater bar, because it might as well be welded in place. I tried various means to get it to loosen up, but finally gave up for fear of wringing it off and possibly damaging the water pump. At this point I'm not confident enough in my ability to get that done before we leave early Monday morning. And, back in the day, I would have waded in and put everything else on hold to get it done. After all, at worst it's just a water pump replacement. But after thinking about it, particularly about the time involved and everything else going on, I decided I’d be better off to just have Jim’s shop do it. I'm grateful that he's willing to work me in, even though he's pretty much booked a week or two in advance. So I put it back together and will take it in today and let them deal with it while I attend to some other matters. It seems that I'm getting more risk-adverse as I get older.

Also, after 22 years my heretofore trusty Rolair compressor decided to stop working, apparently due to a failed pressure switch. Getting a new switch will take some time, as the compressor is so old. So I'll ask Jim to blow out the stack while it's there for the fan replacement.

So two of the three variables I intended to address before this trip will be attended to. The third, the cooling system drain and flush, will have to wait until we return.