hdmod
07-12-2014, 17:41
Hey all,
Bought a 1987 GMC with just 60,000 miles on from Montana last fall.....the truck is a no salt MINT truck........so I drove it very little last fall.........
The truck has a 6.5 engine not the 6.2........the owner changed the original out.......but I did not know it was a 6.5 until I took it to a shop that is sharp with these motors to give it a compression test for the rough idle.....
It has a bit of a rough idle, but starts very quick and clean...... barely a whiff of smoke........
Problem is now with the hot humid weather..........without pulling anything the truck will ramp up to 220 or better if I run it out at 60-65 mph...........
I did not trust the gauge so I put a mechanical in and it reads the same.......
I did change the thermostat but did order it for a 6.2 1987 truck not knowing at the time it had a 6.5..........is the 6.2 and 6.5 thermos the same???? I used a Carquest replacement.........
I am wondering if the wrong thermo would be the issue........
I did put a new fan clutch on and that did not help..........
The rad hoses don't get firm with a lot of pressure and I can take the rad cap off and actually infrared the coolant and it will show a lot cooler........maybe 15-20 degrees cooler.........
Is there a bypass in the thermo housing that isn't blocked properly???
Thanks guys;)
Bought a 1987 GMC with just 60,000 miles on from Montana last fall.....the truck is a no salt MINT truck........so I drove it very little last fall.........
The truck has a 6.5 engine not the 6.2........the owner changed the original out.......but I did not know it was a 6.5 until I took it to a shop that is sharp with these motors to give it a compression test for the rough idle.....
It has a bit of a rough idle, but starts very quick and clean...... barely a whiff of smoke........
Problem is now with the hot humid weather..........without pulling anything the truck will ramp up to 220 or better if I run it out at 60-65 mph...........
I did not trust the gauge so I put a mechanical in and it reads the same.......
I did change the thermostat but did order it for a 6.2 1987 truck not knowing at the time it had a 6.5..........is the 6.2 and 6.5 thermos the same???? I used a Carquest replacement.........
I am wondering if the wrong thermo would be the issue........
I did put a new fan clutch on and that did not help..........
The rad hoses don't get firm with a lot of pressure and I can take the rad cap off and actually infrared the coolant and it will show a lot cooler........maybe 15-20 degrees cooler.........
Is there a bypass in the thermo housing that isn't blocked properly???
Thanks guys;)