97 GMC free wheeling fan clutch leads to upgrades

[SlowBoat]

Had my fan clutch go into free wheel mode on long curvy 2 lane grade with traffic backed up till I made it to a pull off. Let the engine idle with hood up while dash temp gauge dropped from indicated 230 back down to 185. A good 30 minutes with the fan jerking into motion now and again. Happened coming out of Menlo, GA running up to Mentone, AL, in case any of you know the region. Pulling a tandem dual trailer with only about 3 ton load on it. Made it home by taking several cool downs the remaining 30 miles.

Sort of nudged me into my next round of improvements. The fan clutch crapped out, the water pump was squeaking when rotated by hand and the fan I just HAD to add that Duramax fan.

I ordered the 2000 model spin-on water pump version, AC Delco part no. 19168609, a Hayden 2840 Severe Duty fan clutch and a 21" Duramax fan, part no. 15010202. I did the water pump restriction modification by tapping the bypass fitting and installing a pipe plug drilled with a 1/2" hole in it. Everything went fine, no interference with the fan shroud. I had the radiator in the radiator shop for cleaning out while I did the pump swap. I drained the oil and changed to full synthetic oil along with a larger capacity Wix oil filter and changed the air filter too for good measure.

Shakedown run indicated no leaks or problems. But, I did notice that my water temperature never rose above a max of 170 on the dash gauge. It normally ran at the 185 range under normal conditions before my excitement. It would max at 210 under hard loads before falling back to 180-185. I guess I'm adding 2 new AC Delco thermostats part no. 12559336 to my dual thermostat housing.

Next round is the fuel system upgrades!

 

[SlowBoat]

Didn't get the pics added.

 

[SlowBoat]

More pics.View attachment 48453 View attachment 48454 View attachment 48455 View attachment 48454

 

[SlowBoat]

Added the two AC Delco 12559336 thermostats and I'm at a gauge indicated 190 now. Went to a 3 mile grade with trailer and with the AC on I pulled the hill at a max of 205 temp doing 65 MPH, a new best for this rig. The temp dropped back down to 190 within a mile. I'm really starting to get tickled with the upgrades!

 

[JayTheCPA]

Glad to see that a refresh of the cooling stack helped

When I did my repower, I installed a Hayden 2840 and did not like how high it let the ECT go with just a 6,500# RV in tow on minor grades (1% - 3%) and A/C 'On' or 'Off' did not really make a difference. Switched to a Hayden 2886 and ECT's were much easier to manage when I took the RV over 5% - 6% grades with the A/C 'On'. For reference overall, am running 195* F thermostats. So, if the coolant temp wants to peg around the 230*F mark while towing on more serious grades, consider a different fan clutch.

By the way, the dash gauge is known for inaccuracy and non-linear measurement. Seems that the only correct-ish reading is when the needle is around the 210 mark and upward. 160 indicated is actually a *lot* cooler than that. Consider switching over to a digital gauge or get something that reads from the PCM via the OBD-II port.


From what I recall of the other threads about current work on the truck, do not remember seeing any comment about installation of an EGT gauge. Reason for the comment about EGT is that I find the coolant temp on long hard pulls is controllable by how high I let the EGT's go.

 

[THEFERMANATOR]

160 on the gauge is actually 100. If you look on a gas cluster, thats where they start at. And the center hash mark between 160 and 210 is the 180 mark.

 

[Husker6.5]

160 on the gauge is actually 100. If you look on a gas cluster, thats where they start at. And the center hash mark between 160 and 210 is the 180 mark.

And all the other little hash marks in between the numbers are pretty much meaningless - but did make for a nice, balanced, pleasing aesthetic dash layout.

 

[SlowBoat]

Made a 260 mile run that duplicated a previous trip before the thermostat change. Same trailer and same size load. Mileage improved from 13mpg to 16mpg, not exceeding the posted speed limits. Hopefully, an injector change will offer more improvements. Overall, I'm still pleased with my 300K mile truck and expecting to stay after the upgrades.