Finally got around to doing the inline thermostat mod to my '04. Installation went fine and everything seemed ok on the initial startup on the driveway.

However, on the initial drive, the car went up to a temperature of about 206 per my Scan Gauge 2. I considered pulling over, thinking I had a leak, but the reading quickly started going down to 166 in less than one minute. So I continued driving, but the readings continued to rapidly fluctuate, reaching as high as 208 and as low as 161. (Prior to doing the mod, the readings would typically range from 184 to 198, but the rising and falling was always gradual).

When I got home, I let the car idle in the driveway, and the gauge continued doing the same thing, fluctuating up and down between 204 and 171, sometimes dropping or rising as much as 10 degrees in just a few seconds! The other readings on the Scan Gauge (RPM, Intake Air Temp, etc), behaved normally. I checked the connections on the coolant temp sensor as well the sensor located on the radiator near the bottom hose, and they are fine. The dash gauge stays right the middle (as expected).

Does this sound like perhaps a coincidentally failing of the coolant temp sensor? Any other ideas???

 

First, where did you put the thermostat in line? Top hose?

Second, did you drill a small bleed hole in the thermostat and make sure it was oriented up to allow a small amount of coolant flow while cold so hot water can get to the thermostat to open it? Also so air can be bled from the system.

Third, where is the high point in your system? Is it in such a position that you can bleed remaining air out?

 

1. Top hose
2. I used Extinct's kit and the thermostat did have a bleed hole which I orientated per the instructions in the kit.
3. The new thermostat housing seems to be the high point (see pic)

 

@JohnHZ3 Did you coolant level change at all after the drive ?

 

Coolant level was slightly lower after the drive. Maybe 1/2 to 1 cup lower. I topped it up, checked for leaks and then took it out for another quick drive. Same rapid temperature fluctuations. Level very slightly lower

 

Sounds like air in the system.

 

@JohnHZ3 You still have air in the system, once it is all out you coolant level will stay static and your temps should also normalize.

Simplified version, what is happening is an air pocket forms at the thermostat, until that moves or heats up the thermostat stays closed causing the rise in temps above normal. When the thermostat opens your cooling system does it's job and your temps drop rapidly. Then the cycle repeats.

You could :

• Crack the coolant tank cap to prevent pressuring the system
• Start your Disco and run the revs up to 2000 -2500 rpm for a minute
• Let the Disco idle for a minute or so then repeat a few times

Also right after driving with the engine off, squeeze the hose on the engine side of the thermostat a few times, it will help move any trapped air.

With old style thermostat and that location it takes a bit of driving to get the air out.

 

Just to confirm, you did the bleed procedure with the cap off and revving the engine after installation? I suppose it could be a sticking thermostat. I use Motorads so they are top quality, but if it does not settle down in a day or two I will send a replacement.

 

I did the bleed procedure as specified. What is the part number of the thermostat? I was going to buy one locally as a spare.

 

It doesn't look like your connection is on 100% perfect. Regardless this is why I won't use the inline unless I'm permanently living in warm climate. I want to overland, explore and go far north. I'm going to drive the Rover to the Dalton highway north to Alaska this winter. I'll need a thermostat and a TBH for that. Also I think the T-stat keeps the temps more steady and I think that is good for the car.