Modified Thermostat for higher MPG's...

SD26

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There is a 92° Thermostat that is a straight drop-in: Wahler P/N: 4256.92D50. It's real easy to gt to on that as well.
What's stock?

I was thinking about 205 in the A3 too... Almost appears that the A3 and A4 thermostats are the same. Anyone know?
 

Frankencar

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SD26

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Excellent! Thanks, guys!

Thermostats showed up a couple days ago. Should be able to perform the changes to assemble one 205* model this weekend. Waiting for new thermostat cover to show up from ID Parts along with some other maintenance items. I should be able to perform the change next weekend, I believe. I'll be putting in some "old" Evans coolant from one of my Power Strokes that I harvested before its sale last year.

I continue to see operating temperatures on my A4 at around 177F currently, for reference.
 

josh8loop

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Looks like my wife and I are going to pick up a 2005 Mercedes E320 CDI in North Carolina tomorrow. It has 100K on it, and a pretty decent service history. I put a digital thermometer in my suitcase so I can check the coolant temps on the way home. I'm planning on putting a stock T-stat in soon if it needs one, and perhaps making a "Hybrid" T-stat for it too.
 

alloutdoorsboy

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So I got a 92C stat in the passat today and ran it around. SGII recorded 198-207F. 207 going up a long incline. What are the maximum temps you guys are running and does it seem that the higher the temp the better the efficiency??
 

josh8loop

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So I got a 92C stat in the passat today and ran it around. SGII recorded 198-207F. 207 going up a long incline. What are the maximum temps you guys are running and does it seem that the higher the temp the better the efficiency??



Great feedback on the 92 C unit- thanks for the info. With my hybrid 205 unit I usually run from 205-209 F, but lately seems to hover around 206-207 F. Highest I have hit so far is 213 IIRC. Some guys have posted they run slightly higher with the hybrid construction.
 

markd89

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What is a reasonable maximum water temp before there's any risk of overheating -- 220, 230, 240 ?

(I ask because I'm going to rework the cooling system in my engine swap to take it from two radiators down to one and want to know what's safe.)
 

TDIMeister

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It is foolish to reduce cooling capacity. Changing the thermostat merely changes the regulated temperature, but reducing capacity is never a good idea, especially in the LA climate you're in.
 

markd89

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It is foolish to reduce cooling capacity. Changing the thermostat merely changes the regulated temperature, but reducing capacity is never a good idea, especially in the LA climate you're in.
Well, right now, I have much more capacity/coolant volume than a stock TDI. I have double radiators plus the water in the long hoses going to the front heater. Everything works, but warm-up could be quicker.

For the last couple of months, I have cardboard-sandwiched one of the radiators and have been driving around just fine getting the cooling from one radiator. I don't want to actually remove the second radiator until I can test some hills when it's over 100 *F outside and make sure I don't get too hot.

I didn't mean to thread-jack, just wanted to ask how hot is too hot...

Mark
 

TDIMeister

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You fail to recognize that while your particular application has much more capacity than a TDI, it's in a vehicle that is heavier, far less aerodynamic and by the year of your Bus, not one that was ever designed with watercooling in mind. What this means that your particular application would place consistently higher loads upon the engine, therefore more heat needs to be rejected. If your vehicle's warm-up "could be quicker", it is a thermostat issue and more accurately a regulation or thermal management issue.

The simple answer to your original question, "What is a reasonable maximum water temp before there's any risk of overheating -- 220, 230, 240 ?" is some margin below the boiling point of the coolant, which depends on the type, system pressure and concentration you use. If you perceive an overcapacity problem -- completely unrelated to a boiling point problem, which was my original point -- this could be addressed instead of deleting capacity by running higher concentration of ethylene glycol or going to a propylene glycol-based coolant, since they have lower specific heat capacity than water and have higher boiling points to boot.

A "safe" temperature, for the lack of more precision of the intended context and a truly better answer is one that is not far from that extensively engineered in the original engine.
 

markd89

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You fail to recognize that while your particular application has much more capacity than a TDI, it's in a vehicle that is heavier, far less aerodynamic and by the year of your Bus, not one that was ever designed with watercooling in mind. What this means that your particular application would place consistently higher loads upon the engine, therefore more heat needs to be rejected. If your vehicle's warm-up "could be quicker", it is a thermostat issue and more accurately a regulation or thermal management issue.

The simple answer to your original question, "What is a reasonable maximum water temp before there's any risk of overheating -- 220, 230, 240 ?" is some margin below the boiling point of the coolant, which depends on the type, system pressure and concentration you use. If you perceive an overcapacity problem -- completely unrelated to a boiling point problem, which was my original point -- this could be addressed instead of deleting capacity by running higher concentration of ethylene glycol or going to a propylene glycol-based coolant, since they have lower specific heat capacity than water and have higher boiling points to boot.

A "safe" temperature, for the lack of more precision of the intended context and a truly better answer is one that is not far from that extensively engineered in the original engine.
TDIMeister, thanks for your detailed response. I do realize that my vehicle is heavier and not at all aerodynamic. The radiators are mounted underneath which may have less airflow than in-front as well. I knew I was building in too much cooling for the exact reasons you said. There's lots of variables and I wanted to make sure that if I guessed wrong, I would have too much cooling rather than too little.

Changing the fluid to a higher proportion of anti-freeze is an interesting solution. I'll give it some thought.

Thanks much,
Mark
 

dieselfuel

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So I got a 92C stat in the passat today and ran it around. SGII recorded 198-207F. 207 going up a long incline. What are the maximum temps you guys are running and does it seem that the higher the temp the better the efficiency??

235F in the summer. But, as you can see, I'm running the Evans.
 

josh8loop

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Had a hiccup this afternoon I thought I would share. As many of you know, I run the 205 Deg F "Hybrid" T-stat. Since the stage 1 fans come on at a similar temp to where I wanted to run the car at, I dissabled the stage 1 fans by cutting one wire. The stage 2 fans are still functional, and the fans come on as they are supposed to when the AC is kicked on. This afternoon while in extreme stop and go traffic my engine got up a little higher than I was comfortable running. When I looked at it, I was at 216 and climbing. I usually have no issue since I drive in such a way that I am generally always moving so I have natural forced air flow through the radiator. Moral of the story is don't dissable the stage 1 fans unless you devise a circuit to allow you to set the temperature that it comes on. This is what I intend to do in the near future. :D
 

SD26

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So... :D

Did you turn on the AC? Should have kicked on the fans, right?


Assembled my hybrid a little too small. Pressed in the one piece a little too far. Will pop it out a little to match up with a known 195 Stant that I bought to prepare for another hybrid t-stat for my A3 Jetta. Would like to make my A4 Jetta swap Friday along with some "spare" Evans coolant that I have from last years removal from my Excursion.
 

josh8loop

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So... :D

Did you turn on the AC? Should have kicked on the fans, right?


Assembled my hybrid a little too small. Pressed in the one piece a little too far. Will pop it out a little to match up with a known 195 Stant that I bought to prepare for another hybrid t-stat for my A3 Jetta. Would like to make my A4 Jetta swap Friday along with some "spare" Evans coolant that I have from last years removal from my Excursion.


Yes, actually I did turn on the AC reluctantly. My AC compressor has failed internal bearings that make horrible noises at times and I didn't want to allow it to spin. I turned on the heater on high which helped too. I will have to disconnect the AC electrical connector to see if the fans run when I request the AC.

BTW, for informational purposes when the T-stat is installed on the engine the distance from the rear flat thermostat disc and the internal engine passage that it attempts to close is about 1/4" FWIW.
 
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alloutdoorsboy

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Josh, is 216 bad??? I thought folks were running theirs up to 230 with evans, maybe you don't have evans....

On a similar note I put a 92C stat in my passat along with PG coolant (Sierra to flush out the water, will put evans in this weekend). We did this as we put in a new heater core. So now with the temp in the 200F range my heat doesn't seem as hot as before, I know PG doesn't have as much heat capacity as water, is this why the heat is lower??? Anybody else notice this? Im baffled, I assumed with a new core and higher temps I would be roasting. We checked the blender door today and it has full travel.
 

GreenENG

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Hey Guys,

First time posting on this thread, tho i've read through most of it over the last couple months.

Just wondering what is wrong with using the Stant Super Stat? http://www.stant.com/modules/partLocator/view_diagram.cfm?id=45379


I've been using this one since about october, and it seems to be holding up pretty good. Temp comes up a lot quicker than it used to, and it levels out at 96C (~205F) which is what you're aiming for with the Hybrid (i know the specs say 195... but its definetly operating higher than that!)

Anyone tried this one before? Have you run into any major issues?
 

SD26

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Coolant dropped, old thermostat removed. Confirmed that it is the 87C model tstat, OEM standard.

I didn't like the way my hybrid tstat looked compared to my measurement of the Stant 195F. The hybrid I made was shorter. Yesterday, I picked up yet another 195F Stant, and I redid my work, and the lengths were now the same. I pressed the piece in a little too far from the 195F onto the 205F.

Installed, filled the cooling system with some old Evans NPG+. Did a shake down drive. No leaks. Added a little fluid, and took a little longer drive. My Scanguage showed my coolant temperature going above my previous "normal" temperature of 175-177 to its highest point of 207F when I entered the "slower area" of town (25MPH). Idled for a little bit while I did another check for leaks and the fluid level, and the temperature came down to 204F before I shut down.

I filled up last night on the way home. Let the data collection begin.
 

SD26

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SD26,

What was the ambient temp when you did your testing?
I think we were in the upper twenties today. Can't remember what the weather was like last week, but we weren't having that really nice weather like we had. I'd say in the 30's or so?

Things are on going.
 

josh8loop

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Coolant dropped, old thermostat removed. Confirmed that it is the 87C model tstat, OEM standard.

I didn't like the way my hybrid tstat looked compared to my measurement of the Stant 195F. The hybrid I made was shorter. Yesterday, I picked up yet another 195F Stant, and I redid my work, and the lengths were now the same. I pressed the piece in a little too far from the 195F onto the 205F.

Installed, filled the cooling system with some old Evans NPG+. Did a shake down drive. No leaks. Added a little fluid, and took a little longer drive. My Scanguage showed my coolant temperature going above my previous "normal" temperature of 175-177 to its highest point of 207F when I entered the "slower area" of town (25MPH). Idled for a little bit while I did another check for leaks and the fluid level, and the temperature came down to 204F before I shut down.

I filled up last night on the way home. Let the data collection begin.

Your temps sound about like mine with the "Hybrid" unit. I saw those temps when it got in the lower 40's here a while back too so it looks like you are right on par. Summer time temps will stay very similar to what you are seeing aswell. I usually run 205-209 in the summer as opposed to 205-207 in the winter here in Florida. FWIW


Would be interesting to see if you notice any quicker warm ups?(i'm not expecting faster warmups necessarily BTW)
 

SD26

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Would be interesting to see if you notice any quicker warm ups?(i'm not expecting faster warmups necessarily BTW)
You've got great timing... :D

Did a quick test just a little bit ago. Current ambient temperature is 28-29F.

Drove my A3 Jetta with whatever thermostat it has in it with non Evans coolant in it. Starting from cold, Scanguage stated coolant temperature at 30F. Drove my son to school a seven mile one way trip that has two five stop signs very early on followed by a run to school at 55MPH, then slowing down into town. My temperature at school was about 177F over that seven mile stretch. Total round trip distance was 14 miles

The route back starts with three stop signs, then the run back home at 55MPH into town where I have two stop signs to deal with. My temperature at home was about 188F.

In contrast, my Jetta A4 with the hybrid tstat, Evans NPG+, and the overall OEM gearing allowing the RPMs to be lower at the same speed, my starting cold temperature was 28F. At school arrival (no child for the drop off, but I did do a courtesy stop for research...LOL!), the Scangauge temperature was around 166F. At my arrival at home, my temperature was 200F.


The reason for my test was that it I'm mentally struggling with "how" my A4 warms up. Over the same distance, I eventually achieve a higher temperature, as expected (assuming that my A3 has a thermostat of 187 to 192F). But I'm struggling with the warm up at my half way point: I think that my A4 should similarly warm as my A3 on the first part of this route. One part of me is thinking that this is the result of the Evans coolant, and another part of me is questioning my assembly of the thermostat.
I will fill up tonight as I'll have about 330 miles on this first tank following the change of the thermostat that was in my A4 and the change to Evans coolant.

I could change the coolant in the A3 and do another back to back drive of both cars to control for ambient temperature, and that might be the easiest way to come up with some answers.
 
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josh8loop

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You've got great timing... :D

Did a quick test just a little bit ago. Current ambient temperature is 28-29F.

Drove my A3 Jetta with whatever thermostat it has in it with non Evans coolant in it. Starting from cold, Scanguage stated coolant temperature at 30F. Drove my son to school a seven mile one way trip that has two five stop signs very early on followed by a run to school at 55MPH, then slowing down into town. My temperature at school was about 177F over that seven mile stretch. Total round trip distance was 14 miles

The route back starts with three stop signs, then the run back home at 55MPH into town where I have two stop signs to deal with. My temperature at home was about 188F.

In contrast, my Jetta A4 with the hybrid tstat, Evans NPG+, and the overall OEM gearing allowing the RPMs to be lower at the same speed, my starting cold temperature was 28F. At school arrival (no child for the drop off, but I did do a courtesy stop for research...LOL!), the Scangauge temperature was around 166F. At my arrival at home, my temperature was 200F.


The reason for my test was that it I'm mentally struggling with "how" my A4 warms up. Over the same distance, I eventually achieve a higher temperature, as expected (assuming that my A3 has a thermostat of 187 to 192F). But I'm struggling with the warm up at my half way point: I think that my A4 should similarly warm as my A3 on the first part of this route. One part of me is thinking that this is the result of the Evans coolant, and another part of me is questioning my assembly of the thermostat.
I will fill up tonight as I'll have about 330 miles on this first tank following the change of the thermostat that was in my A4 and the change to Evans coolant.

I could change the coolant in the A3 and do another back to back drive of both cars to control for ambient temperature, and that might be the easiest way to come up with some answers.


That is funny how the timing worked out! :)
I seem to remember that there are for sure differences on how both those cars warm up, but can't remember specifics. I'm sure other guys will chime in about that. I can say however that as long as you are reasonably close(within .010) to the same overall physical length on the "Hybrid" as compared to the 195 Stant stock type T-stat then you will be good to go. By the results of your temperatures it looks like you did a good job with the construction otherwise your results would be different. Looking forward to your results after a few full tanks of fuel pass through.
 

dieselfuel

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Hooked up my VCDS today and went for a cruise (!). Ambient temp was about 32F. I saw a high of 106.3C via measuring blocks.

I did not check the coolant tank temp, as my digital thermometer isn't working. :> (

106.3C = 225.4F
 

SD26

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That is funny how the timing worked out! :)
I seem to remember that there are for sure differences on how both those cars warm up, but can't remember specifics. I'm sure other guys will chime in about that. I can say however that as long as you are reasonably close(within .010) to the same overall physical length on the "Hybrid" as compared to the 195 Stant stock type T-stat then you will be good to go. By the results of your temperatures it looks like you did a good job with the construction otherwise your results would be different. Looking forward to your results after a few full tanks of fuel pass through.
Well, my results are certainly changing... LOL!

Just got home. My commute is about 27 miles long. Scangauge stated my starting coolant temperature at 35F, and I think the ambient temperature was right around 29F.

Long story short: I was not able to hit 200F on the way to work nor on the way home. I got to 193F on the way home. That was at 55MPH just outside of town, then I slow to 45, 30, then 25 and into my driveway. Temp dropped to low 170's in that mile of slowing down. So, something is amiss with my thermostat.

Filled up with fuel. Did get 51.5MPG. Slight improvement over some of my data, but, intuitively, the temperatures just haven't seemed right...and are now certainly getting worse. All seems to be going in the right direction, but I'll have to revisit the thermostat assembly.
 

SD26

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Dropped the Evans coolant, removed the hybrid tstat I made. Really appears to be the same length as the 195F that I have in my hand.

Used a scale I had in the garage, crude, and pushed on the top hat portion of each to see if one had less spring rate that I could recognize. Nothing obvious at all.

Did find a Wahler 198F tstat on line last night/this morning, and I ordered that just to have for inventory/use/testing. My debate right now it whether I should just put in the Stant assembled 195F tstat to get back to some consistency for data collection until I can figure out what I did wrong with my hybrid assembly...and I think that's the route I should follow right now.

195F going in for now...
 

SD26

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Where did you find that Wahler 198F stat ?????
Was late last night or in the morning, depending upon how you look at it... :D

http://www.thepartsbin.com/catalog/?N=&uts=true&Ntt=W0133-1633589&x=0&y=0

I think I'll put that one in my older Jetta, and continue work on the hybrid for my A4.


The 195F thermostat was good. Didn't have the drop off of temperatures like yesterday. Temp came up that seemed normal, and then it maintained its temperature right around 197 to 200F with it touching a couple degrees on either side occasionally. Would still like those extra ten degrees though... Rain tomorrow, so, I'm unsure if I can get it done. Will finish my oil change that I started (the drain part) in the morning.

Tracking number is saying that I'll have the thermostat tomorrow also. Can't complain!
 
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