[Greck]

Today I replaced the thermostat, spent 3 hours, one note here: I removed the big fan to make it more easier. Drained the system from the bottom(transmission radiator). Currently temp is stable 88-89C.

[335dsleeper]

^ good stuff. Glad it worked out.

[Persian Whisperjet]

Have to admit I was concerned that my thermostat might be getting tired at 78K miles. I logged some temps yesterday driving down I-270 using iCarly and was surprised by precisely how close the temp stayed to 90 degrees.

[Persian Whisperjet]

Here's another, with engine speed added. As you can see, coolant temps are very stable right around 90, but strangely, when I punch the skinny pedal temps *drop* slightly. Anyone understand what is going on here?

[335dsleeper]

You're moving coolant through the engine faster when at operating temperature and when you increase RPMs. The faster you drive, the faster air passes through the radiator, which will pull the heat from the radiator quicker.

[Persian Whisperjet]

Originally Posted by 335dsleeper

You're moving coolant through the engine faster when at operating temperature and when you increase RPMs. The faster you drive, the faster air passes through the radiator, which will pull the heat from the radiator quicker.

I assume that principle only holds for short blips, correct? Otherwise coolant temps would be lowest when driving at Vmax.

[335dsleeper]

Well, in my limited experience, I've never overheated an engine on the hwy, even very aggressive hwy driving.

I've also never experienced an overheating situation on long WOT applications on the road course. Car would always get warm in low speed sections of the track and you'd use the straight to apply WOT and cool her down.

[Yozh]

Folks, change your thermostats early. Good time to do when you are doing the balancer when all the belts are off. Also, as a suggestion, change all three (3) bleeder screw to brass/aluminum to avoid leaks in the future. Below pictures should be self explanatory.

[Mark M]

Just finished changing mine this morning and the glow plug controller. Suggest replacing the thermostat bolts with new while in there. Reusing the old ones just felt like a mistake the threads felt sloppy. New bolts did the trick.

[TorqueAddict]

I got mine replaced yesterday. Before, the maximum temperature i was able to hit was 64C. After the replacement, it went to a solid 85C. Mine did not had any visible damage or was not cracked.

[TorqueAddict]

oh, and i also noticed an increase in fuel economy. According to on board calculations, it used to show 7.9-8L/100 km and on the same route last night, i got 5.9-6.1L/100km

[Mark M]

Agreed. My old Tstat was not broken in any spots but was only reporting back temps around 70C. The new Tstat is showing temps around 86C. The car warms up in ~10 minutes in 36 degree weather.

MPG has improved incrementally as well. On winter diesel fuel, after 220 miles of mixed driving I am showing 37.3 MPG.

Recommend this maintenance to all 35d owners. The part is only ~$40, win win.

[lnxguy]

Originally Posted by TorqueAddict

I got mine replaced yesterday. Before, the maximum temperature i was able to hit was 64C. After the replacement, it went to a solid 85C. Mine did not had any visible damage or was not cracked.

Where'd you source your t-stat from if you don't mind me asking?

[TorqueAddict]

Originally Posted by lnxguy

Where'd you source your t-stat from if you don't mind me asking?

My indie ordered it for me. I can PM you his shop details if you would like.

[Dazza335iC]

Originally Posted by Yozh

Folks, change your thermostats early. Good time to do when you are doing the balancer when all the belts are off. Also, as a suggestion, change all three (3) bleeder screw to brass/aluminum to avoid leaks in the future. Below pictures should be self explanatory.

Attachment 1525741

Same exact thing happened to mine. It seems the 35d thermostats are a known weak point.

[nicklockard]

Originally Posted by Dazza335iC

Same exact thing happened to mine. It seems the 35d thermostats are a known weak point.

ALL thermostats are a weak point. It's the technology: modern T-stats are designed around a wax phase-change pellet and have 2-stage behavior. The wax pellets become degraded over time (about 8-12 seasons, depending on how bad the seasonal swings are) and they fail to COLD because the wax pellets allow stage one early opening to occur earlier.

It's just a technological limitation. I'd wager that 75% of cars on the road today have t-stats running colder than designed temperature specifications. Nearly every used car I've ever put my OBD scanner to ran colder than spec.

[Dazza335iC]

Originally Posted by nicklockard

ALL thermostats are a weak point. It's the technology: modern T-stats are designed around a wax phase-change pellet and have 2-stage behavior. The wax pellets become degraded over time (about 8-12 seasons, depending on how bad the seasonal swings are) and they fail to COLD because the wax pellets allow stage one early opening to occur earlier.

It's just a technological limitation. I'd wager that 75% of cars on the road today have t-stats running colder than designed temperature specifications. Nearly every used car I've ever put my OBD scanner to ran colder than spec.

I was referring more to the plastic tabs that hold the thermostat in the housing, than to the materials that make up the thermostat. Those tabs seem to break all the time. Compare that to the thermostat design on earlier BMWs (e30, e34, e46, etc) where the thermostat is the same part but not clipped in to the housing. Those rarely, if ever, failed, because the thermostat material itself is rarely the cause of the failure.

[digitaldav]

Originally Posted by lnxguy

Where'd you source your t-stat from if you don't mind me asking?

Rock Auto has always treated me well.

BECK/ARNLEY 1430904 {#11517805811} Info
OE TEMPERATURE; Includes Thermostat
$38.79
Add Part

Add Part
MAHLE/CLEVITE TI23488 {#11517805811} Gasket or Seal Included
Start to Open Temperature 88 C
$52.89
Add Part

[nicklockard]

Originally Posted by Dazza335iC

I was referring more to the plastic tabs that hold the thermostat in the housing, than to the materials that make up the thermostat. Those tabs seem to break all the time. Compare that to the thermostat design on earlier BMWs (e30, e34, e46, etc) where the thermostat is the same part but not clipped in to the housing. Those rarely, if ever, failed, because the thermostat material itself is rarely the cause of the failure.

Okay, thanks for clarification and a good point. My t-stat I just replaced had those tabs intact. The few I've personally replaced had bad/old wax pellets with intact tabs. Different failure modes for different designs. My main point is general and not aimed at you in particular: keep an eye on temperatures because cold temps hurts fuel economy, emissions, and power.

[captpilly]

Where can you find the new screws?

Is this right? M6 x 20

http://www.pelicanparts.com/cgi-bin/...&I1.x=0&I1.y=0

[Mark M]

Yes, M6 x 20. 4 of them.

[Mark M]

Not to beat a dead horse on this one.....but the thermostat change really has made a world of difference.

- MPG is up at 37.9 mpg. I have done 320 miles on half a tank and OBC is projecting this to be a 635 mile tank based on current consumption. Previously I was only seeing about 550 mile tanks or less ~34 / ~32 mpg.
- Warm ups are shorter. The car reaches ideal running temps in about 10 minutes.
- Transmission shifts feel more crisp and precise. I know this sounds odd, maybe placebo effect.
- Low rpm performance feels more responsive, pulling away from a light or slow driving, the pedal feels more linear, again maybe placebo effect.
- And less soot on the rear (ABC delete car)

This might classify as one of the best and cheapest 'mods' done to the car.