2010.02.05 - Thermostat Replacement
- Drained coolant and removed old thermostat
- Modified new thermostat by adding a bypass hole
- Installed new thermostat
- Filled and purged cooling system
- Replaced brake fluid in clutch and brake master cylinders
I don't think I've mentioned it here before, but since mid-December I've noticed that the car does not seem to be getting up to temperature properly. During one particular coldsnap of weather, I took a trip up to Houston and the water temps barely rose above 130 degrees while on the highway. Based on the symptoms, I suspected either a thermostat stuck open or a ruptured gasket, but both seemed sort of unlikely. Yesterday I finally got a chance to crack the cooling system open and determine what's going on with my thermostat.
So what was the culprit? The primary problem was a 3/16" bypass hole where the "jiggle-pin" somehow bored its way through the thermostat plate (and is now probably floating around in the top of my radiator). Additionally, the thermostat that was included with the reroute kit was a 180-degree thermostat. The slightly lower temp rating wasn't really a big issue (and 180 is a common alternate option for my model year Miata), but in combination with the over-sized bypass I just couldn't build up enough heat to keep the car at operating temperature unless the car was at a stationary idle. From looking at the old thermostat I would guess that the jiggling action of the jiggle pin was intense or excessive enough that it basically drilled/hammered its way through the thermostat flange. So it looks like this may have been an inevitable design failure and has very little to do with the cold weather.
In a remote horizontal setup like the M-Tuned reroute uses, having a tiny bypass in the thermostat flange is a good idea as it allows air to purge on first fillup as well as allowing the heated water to reach the thermostat quicker. It's not necessarily mandatory, but it's not a bad idea. However, since I was paranoid about the same thing happening again with the jiggle-pin, I opted to go with a traditional thermostat (which does not have a bypass) and drill a tiny hole in the flange. I drilled a 1/16" hole and later drilled it out to 5/64" (though that was probably not necessary) in an attempt to get roughly the same opening area that the previous thermostat had when the jiggle pin was still properly in place. This should provide the same functionality without the risk of the pin tearing up the thermostat again.
By itself, the 180 thermostat shouldn't be an issue (and it seemed to do fine last summer), but I since I have never had cooling problems with the OEM 192 thermostat I opted to go back with a 195-degree Stant "SuperStat" thermostat this time around.
I ran and purged the system last night and it seems to be functioning as desired so far, but I have yet to take a real test drive.
While I had the hood open, I went ahead and replaced the old brake fluid in the master cylinders with some fresh fluid.
$7.62 - Thermostat, gasket, drain-plug o-ring
Notes:
727-2111 - O-ring for radiator drain plug (* I'd actually like something slightly thicker, but this should still work sufficiently.)
1070 - Thermostat gasket (* This is not exactly like the one that came with the reroute kit, but it seems to be a good fit. I might try to find one with a slightly larger OD next time I have to replace it though.)
530090 - 195F SuperStat w/o jiggle pin
Alternate Thermostat Options:
530080 - 180F w/o jiggle pin
536090 - 195F w/ jiggle pin
536080 - 180F w/ jiggle pin
Alternate Thermostat Gasket Options:
1093
- Modified new thermostat by adding a bypass hole
- Installed new thermostat
- Filled and purged cooling system
- Replaced brake fluid in clutch and brake master cylinders
I don't think I've mentioned it here before, but since mid-December I've noticed that the car does not seem to be getting up to temperature properly. During one particular coldsnap of weather, I took a trip up to Houston and the water temps barely rose above 130 degrees while on the highway. Based on the symptoms, I suspected either a thermostat stuck open or a ruptured gasket, but both seemed sort of unlikely. Yesterday I finally got a chance to crack the cooling system open and determine what's going on with my thermostat.
So what was the culprit? The primary problem was a 3/16" bypass hole where the "jiggle-pin" somehow bored its way through the thermostat plate (and is now probably floating around in the top of my radiator). Additionally, the thermostat that was included with the reroute kit was a 180-degree thermostat. The slightly lower temp rating wasn't really a big issue (and 180 is a common alternate option for my model year Miata), but in combination with the over-sized bypass I just couldn't build up enough heat to keep the car at operating temperature unless the car was at a stationary idle. From looking at the old thermostat I would guess that the jiggling action of the jiggle pin was intense or excessive enough that it basically drilled/hammered its way through the thermostat flange. So it looks like this may have been an inevitable design failure and has very little to do with the cold weather.
In a remote horizontal setup like the M-Tuned reroute uses, having a tiny bypass in the thermostat flange is a good idea as it allows air to purge on first fillup as well as allowing the heated water to reach the thermostat quicker. It's not necessarily mandatory, but it's not a bad idea. However, since I was paranoid about the same thing happening again with the jiggle-pin, I opted to go with a traditional thermostat (which does not have a bypass) and drill a tiny hole in the flange. I drilled a 1/16" hole and later drilled it out to 5/64" (though that was probably not necessary) in an attempt to get roughly the same opening area that the previous thermostat had when the jiggle pin was still properly in place. This should provide the same functionality without the risk of the pin tearing up the thermostat again.
By itself, the 180 thermostat shouldn't be an issue (and it seemed to do fine last summer), but I since I have never had cooling problems with the OEM 192 thermostat I opted to go back with a 195-degree Stant "SuperStat" thermostat this time around.
I ran and purged the system last night and it seems to be functioning as desired so far, but I have yet to take a real test drive.
While I had the hood open, I went ahead and replaced the old brake fluid in the master cylinders with some fresh fluid.
$7.62 - Thermostat, gasket, drain-plug o-ring
Notes:
727-2111 - O-ring for radiator drain plug (* I'd actually like something slightly thicker, but this should still work sufficiently.)
1070 - Thermostat gasket (* This is not exactly like the one that came with the reroute kit, but it seems to be a good fit. I might try to find one with a slightly larger OD next time I have to replace it though.)
530090 - 195F SuperStat w/o jiggle pin
Alternate Thermostat Options:
530080 - 180F w/o jiggle pin
536090 - 195F w/ jiggle pin
536080 - 180F w/ jiggle pin
Alternate Thermostat Gasket Options:
1093