Thought I'd report on the performance and tech of our 97 while towing a 6000lb travel trailer through Utah's canyon lands and national parks, since so many seem to have overheating issues. We got home yesterday. She has 244,000 miles and got a new radiator at 130,000, and a new blue fan clutch a couple years ago just as PM. Totally stock right down to the Michelins. Last year she got a coolant flush and thermostat. Just before leaving, I put new spark plugs in - stock type - lubed the driveshafts, and put on a new a/c belt. Every year I do a drain and fill of the auto trans, which changes out about a third of the fluid. So essentially just meticulous maintenance.
We traveled 3001 miles and over about 15 passes over a mile high, and 3 of these were over 9000 feet - one close to 10,000. The temp was typical Utah desert in July - hovering right around 100. Many of these I was in 2nd gear at 3000rpm and 45mph ish, but for the really bad ones I was in 1st gear at 3000rpm at about 25mph. Really brutal conditions, and the truck seemed to handle it well. Gauge went up a half needle width, but oil pressure held steady (Rotella Synth) and no issues with brakes or other systems.
One one truly steep and really high pass, I turned off the a/c and turned on the heat full blast with the windows down because I was really worried. I was pulling so much heat off the engine that way that a strange thing happened. When we crested the pass, I pushed the temp control back to cold but did not turn on the a/c because the outside air up that high was actually comfortable. But the vents kept putting out hot air. Really hot. A full 30 seconds later, still putting out full hot air. I couldn't believe the hot water valve had evidently failed and I was going to have to stop and manually move it. A full minute went by and now I was sure of it. Then, the heat diminished just slightly and I realized that I had put so much heat into the heater core, the entire dash ducting and other components that it had taken that long simply to push the heat out of the system. It took a full 5 minutes to cool. I've never experienced that before but it shows just how effective that strategy is if you ever need to do it yourself to prevent an overheat. I was pulling an enormous amount of heat off the engine's load that way and happy to have that evidence.
We burned fuel like beer at a frat party - 7.14 miles per gallon for one memorable tank. Typically we got 10.3 MPG. After disconnecting the trailer and driving home at 68mph with a rooftop tent still on we got 14mpg without the trailer.
One additional comment. Many of you have complained about a faint idle stumble which this 97 has also. My 93 doesn't do it - smooth classic straight 6 idle like butter. Well, when I changed the plugs on this 97, I found one of them looser than the others even though I use a torque wrench and anti sieze. When I put the new plugs in (last ones were in 95,000 miles) that stumble was gone and it was there for years. Smooth as butter. The old plugs looked uniform and worn but the slightly loose plug had some crud into the threads as though it was actually allowing some blowby.
Also, I always used the highest octane I could find while towing in the desert. So if you are having overheat issues, consider doing what it takes to bring your 80s cooling system back as close to new as possible and you may find your donkey will again faithfully work hard for you.
Regards,
DougM
We traveled 3001 miles and over about 15 passes over a mile high, and 3 of these were over 9000 feet - one close to 10,000. The temp was typical Utah desert in July - hovering right around 100. Many of these I was in 2nd gear at 3000rpm and 45mph ish, but for the really bad ones I was in 1st gear at 3000rpm at about 25mph. Really brutal conditions, and the truck seemed to handle it well. Gauge went up a half needle width, but oil pressure held steady (Rotella Synth) and no issues with brakes or other systems.
One one truly steep and really high pass, I turned off the a/c and turned on the heat full blast with the windows down because I was really worried. I was pulling so much heat off the engine that way that a strange thing happened. When we crested the pass, I pushed the temp control back to cold but did not turn on the a/c because the outside air up that high was actually comfortable. But the vents kept putting out hot air. Really hot. A full 30 seconds later, still putting out full hot air. I couldn't believe the hot water valve had evidently failed and I was going to have to stop and manually move it. A full minute went by and now I was sure of it. Then, the heat diminished just slightly and I realized that I had put so much heat into the heater core, the entire dash ducting and other components that it had taken that long simply to push the heat out of the system. It took a full 5 minutes to cool. I've never experienced that before but it shows just how effective that strategy is if you ever need to do it yourself to prevent an overheat. I was pulling an enormous amount of heat off the engine's load that way and happy to have that evidence.
We burned fuel like beer at a frat party - 7.14 miles per gallon for one memorable tank. Typically we got 10.3 MPG. After disconnecting the trailer and driving home at 68mph with a rooftop tent still on we got 14mpg without the trailer.
One additional comment. Many of you have complained about a faint idle stumble which this 97 has also. My 93 doesn't do it - smooth classic straight 6 idle like butter. Well, when I changed the plugs on this 97, I found one of them looser than the others even though I use a torque wrench and anti sieze. When I put the new plugs in (last ones were in 95,000 miles) that stumble was gone and it was there for years. Smooth as butter. The old plugs looked uniform and worn but the slightly loose plug had some crud into the threads as though it was actually allowing some blowby.
Also, I always used the highest octane I could find while towing in the desert. So if you are having overheat issues, consider doing what it takes to bring your 80s cooling system back as close to new as possible and you may find your donkey will again faithfully work hard for you.
Regards,
DougM
According to the stock gauge dead range and the sparse documentation, the acceptable temp range is pretty wide and you were likely inside of it, maybe, barely? 
