How many holes did you drill in the thermostat. I noticed after I went from 1 to 2 (1/8 inch) holes I tended to drop colder when cruising on the highway off the gas. What I suspect is when rolling down the MTN the thermostat is closed in an attempt to stop flow to the radiators, to prevent cooling. With the hole(s) drilled in the thermo, some hot coolant is leaking through and being cooled thus lowering the coolant temp.

On a side note, does anyone run the inline thermo without any holes?

 

Ambient temps will always be a factor. If your engine warms up and constantly produces heat under load it will operate at near the designed temps. However if you're basically at idle going down a mountain the air being pushed thru the radiator is going to cool it down past that temp. That's why you'll see 18 Wheeler's with those radiator guards on them when it gets cold. It reduces the air flow thru the radiator to maintain the proper temps in cold weather. My friend in Wyoming is having to block off his D2's radiator some in order for it to run warmer.

 

I haven't done the mod yet but from what I read, the 1/8" drilled hole is to help in bleeding air from the system when installed at the 12 o'clock position.

 

Hole will help bleeding, but reason for it is to pass coolant trough T-stat to get it to open at proper temp, you can get away with one 1/8" hole, but I did 2 holes & installed jiggle pins in them , to prevent holes from clogging, (so almost like having as much flow as one hole),

 

Ah that's what it's going to be, write up I followed suggested 2 holes and that's what I did. I'm going to get another thermostat and drill only one hole and monitor for change. I have another snow run coming up in February I can test it on.

 

Mine doesn't have a hole or a jiggle doodad. Works fine. It had not occurred to me, until I read in this thread, that the hole may help the thermostat open (by allowing coolant to circulate past it) and that makes good, logical sense.

I also swapped the location of the thermostat housing and the other part (name escapes me, with valve) to put the thermostat closer to the block. With the valve in the middle of the fan shroud, I just put a can of whatever underneath it (for elevation) to get air out.