My wife's 98 XLT 4x4 SOHC has intermittently run the thermostat gauge up to the top when running the A/C. It concerned us both, so I replaced it Thursday before our weekend trip to the hills. With 66K on it, I didn't think it unreasonable that a new thermostat would be required ($19 or so at NAPA, plus the O-ring).
The amount of disassembly required to get in there is a little unreasonable, but eminently doable. Taking off the intake tube/MAF assembly got me some of the way there, but it was also neccessary to remove the TB. If I had done that right away, it would have saved a lot of time. I estimate that the thermostat plus the serpentine belt R&R should take no more than 45 min for someone of modest skills (e.g. me).
At any rate, I pulled the plastic housing apart (yes, plastic) and found a whole factory thermostat plus the lower spring and valve from another factory thermostat. For 66K the truck has run with an extra lower valve plate covering the water pump intake! Looking at it, when the engine was assembled, the first thermostat must have broken the retaining clip and popped apart. Another thermostat was inserted on top without removing the remains of the broken thermostat.
It was initially confusing, so much so that I stupidly refitted the valve and spring to see what in the world was going on. It was dumb luck I didn't drop the spring into the water pump! I do wonder where that retaining clip went....
At any rate, I put it all back together and got the desired results. With about 200 miles on that tank, it was going to be time to gas up soon. When we did gas up at 251 miles, my wife remarked that she'd NEVER gotten that many miles on a tank.
I may have to apologise to my wife for teasing her about her lead foot - it may be that the 12-14 mpg observed in the last 66K miles is due more to a faulty thermostat than to her throttle managment.
I would point out that even offroading in Death Valley never precipitated any overheating or other manifestation of mechanical distress. I can't imagine how enough coolant got past that second valve smashed in there, but it did.
Regards,
Brian in CA
The amount of disassembly required to get in there is a little unreasonable, but eminently doable. Taking off the intake tube/MAF assembly got me some of the way there, but it was also neccessary to remove the TB. If I had done that right away, it would have saved a lot of time. I estimate that the thermostat plus the serpentine belt R&R should take no more than 45 min for someone of modest skills (e.g. me).
At any rate, I pulled the plastic housing apart (yes, plastic) and found a whole factory thermostat plus the lower spring and valve from another factory thermostat. For 66K the truck has run with an extra lower valve plate covering the water pump intake! Looking at it, when the engine was assembled, the first thermostat must have broken the retaining clip and popped apart. Another thermostat was inserted on top without removing the remains of the broken thermostat.
It was initially confusing, so much so that I stupidly refitted the valve and spring to see what in the world was going on. It was dumb luck I didn't drop the spring into the water pump! I do wonder where that retaining clip went....
At any rate, I put it all back together and got the desired results. With about 200 miles on that tank, it was going to be time to gas up soon. When we did gas up at 251 miles, my wife remarked that she'd NEVER gotten that many miles on a tank.
I may have to apologise to my wife for teasing her about her lead foot - it may be that the 12-14 mpg observed in the last 66K miles is due more to a faulty thermostat than to her throttle managment.
I would point out that even offroading in Death Valley never precipitated any overheating or other manifestation of mechanical distress. I can't imagine how enough coolant got past that second valve smashed in there, but it did.
Regards,
Brian in CA
