Modified Thermostat for higher MPG's...

94cobra2615

Veteran Member
Joined
Jun 16, 2013
Location
ohio
TDI
2002 Black Wagon
I just went to advance auto parts and ordered one there. That one looks like josh's stat and I went ahead and did the modification to it and installed it.

The thermostat that doesn't look the same that I got initially I ordered from Rockauto. Aparently there are two versions of the same part number from stant. I'm not sure if rockautos is a newer version or older.

Car stays around 203 degrees. I tried to push it out on the road and I never got it above 204.8 degrees, so it seems to be working according to Ultragauge.

My previous thermostat was an oem one replaced last year and it usually hovered around 180.
 

G3TDI

Veteran Member
Joined
Jan 19, 2011
Location
CA
TDI
1994 Golf TDI http://forums.tdiclub.com/showthread.php?t=305898
I just went to advance auto parts and ordered one there. That one looks like josh's stat and I went ahead and did the modification to it and installed it.

The thermostat that doesn't look the same that I got initially I ordered from Rockauto. Aparently there are two versions of the same part number from stant. I'm not sure if rockautos is a newer version or older.

Car stays around 203 degrees. I tried to push it out on the road and I never got it above 204.8 degrees, so it seems to be working according to Ultragauge.

My previous thermostat was an oem one replaced last year and it usually hovered around 180.
OK great, do you have pics of the two boxes and all the numbers and labeling on them?
 

hardint

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Joined
Jan 16, 2004
Location
Ky
TDI
2000 gl
I purchased the stant also only to find that it isn't made the same as described ,I did that last winter and it's still laying in tool box I will look at it and recheck this post, hopefully the 94cobra will post pictures also to help find the correct part with same part numbers.
I have several gallons of Evans around also hadn't thought of the higher temp helping keep me warm in the cold,I hate the warm up time of the TDI in winter !!!
 

hardint

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Jan 16, 2004
Location
Ky
TDI
2000 gl
Thanks 94cobra, I will compare to my box tomorrow if I don't forget but reasonably sure it looks like the wrong one box on the right !!!
Are they both USA made or one Mexico or China ??
 
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G3TDI

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CA
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1994 Golf TDI http://forums.tdiclub.com/showthread.php?t=305898
So I've been loving my hybrid thermostat & evans coolant setup now for some time, so much so that I plan to use it on a TDI swap into a larger vehicle :)

This vehicle I also plan to tow with on occasion, whereby I have considered using an external oil cooler also but not sure if that's a good idea at all, even if I used a sandwich that has a thermostat builtin I am thinking it could work "against" this higher temp thermostat? Thoughts?
 

clyde

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Apr 8, 2000
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confluence, Snake/Clearwater
TDI
1998 Jetta, 1959 DeSoto with leopard-skin seat covers
The oil temp affects coolant temp only indirectly.

In November I towed a 2300 pound load 500 miles with a Mk3 TDI, which had the factory oil cooler. Temps didn't exceed 230°F going uphill. Of course, with that load I wasn't driving 80 mph—55 was more like it.

You might have to try it and see.
 

G3TDI

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CA
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1994 Golf TDI http://forums.tdiclub.com/showthread.php?t=305898
The oil temp affects coolant temp only indirectly.

In November I towed a 2300 pound load 500 miles with a Mk3 TDI, which had the factory oil cooler. Temps didn't exceed 230°F going uphill. Of course, with that load I wasn't driving 80 mph—55 was more like it.

You might have to try it and see.
Well it depends on how "indirectly" you mean :)

As long as you have the factory ("oil cooler" as they call them) heat exchanger, the coolant will be heating up the oil when engine is cold, and vice versa when the engine is warm.

The factory "oil cooler" is not really an "oil cooler" in the same sense as an external one would indeed be a cooler, hence the question.

P.S. Where exactly are you measuring the oil temp? http://forums.tdiclub.com/showthread.php?p=3585250
 

clyde

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confluence, Snake/Clearwater
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1998 Jetta, 1959 DeSoto with leopard-skin seat covers
Installed a VW sensor "at the engine inlet (post oil filter/heat exchanger)," which is atop the filter adapter on a Mk3 AHU engine.
 

G3TDI

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CA
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1994 Golf TDI http://forums.tdiclub.com/showthread.php?t=305898
Installed a VW sensor "at the engine inlet (post oil filter/heat exchanger)," which is atop the filter adapter on a Mk3 AHU engine.
Ok that's where I was considering putting one too, what gauge are you using? I am also using the AHU engines btw.

Interesting question, have you ever measured (as in followed during driving) the coolant temp vs oil temp? The factory coolant gauge is very inaccurate, I can say this because I barely notice my factory coolant gauge being higher than straight up even with my 205F/96C thermostat which according to to my scanguage gives me a coolant temp of 105-112c (221-233F)
 
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clyde

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Location
confluence, Snake/Clearwater
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1998 Jetta, 1959 DeSoto with leopard-skin seat covers
As an experiment I put VW temp sensors in both the filter adapter flange, for oil temp, and in the coolant outlet flange for coolant temp. Ran the outputs of both sensors to a single-pole, double throw switch. Output of the switch went to the input of the MFA of a Mk2 instrument cluster. By selecting the MFA Oil Temp function the readout would show oil temp or coolant temp, depending on the setting of the SPDT switch.

As you said, at engine start the coolant heats much more rapidly than does the oil, and the small oil-coolant heat exchanger warms the oil—good for a cold engine.

After heat stabilizes, coolant and oil temps weren't much different.

I agree about the crummy coolant temp gauges on the Mk3. Mine will show a temp decline on a long downhill run, but it doesn't show an increase on a long uphill climb.

On my Mk3 I also use the MFA readout to monitor oil temp. Have a modified cluster from a V6 car…
 

G3TDI

Veteran Member
Joined
Jan 19, 2011
Location
CA
TDI
1994 Golf TDI http://forums.tdiclub.com/showthread.php?t=305898
As an experiment I put VW temp sensors in both the filter adapter flange, for oil temp, and in the coolant outlet flange for coolant temp. Ran the outputs of both sensors to a single-pole, double throw switch. Output of the switch went to the input of the MFA of a Mk2 instrument cluster. By selecting the MFA Oil Temp function the readout would show oil temp or coolant temp, depending on the setting of the SPDT switch.

As you said, at engine start the coolant heats much more rapidly than does the oil, and the small oil-coolant heat exchanger warms the oil—good for a cold engine.

After heat stabilizes, coolant and oil temps weren't much different.

I agree about the crummy coolant temp gauges on the Mk3. Mine will show a temp decline on a long downhill run, but it doesn't show an increase on a long uphill climb.

On my Mk3 I also use the MFA readout to monitor oil temp. Have a modified cluster from a V6 car…
Cool, thanks!

Do you have any of the mods discussed in this thread also? "Hybrid" thermostat and/or waterless coolant?
 

94cobra2615

Veteran Member
Joined
Jun 16, 2013
Location
ohio
TDI
2002 Black Wagon
Just an update on my hybrid thermostat. With the hotter temps of summer I've seen a temp as high as 217.8 degrees in a traffic jam with the air on.

Normal temps have been around 206 to 212 with the summer temps.

Car runs great regardless of the temps!
 
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turbovan+tdi

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Mar 23, 2014
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Abbotsford, BC.
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2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
Any MPG gain?

Mine with a new OEM stat runs at 93 deg C with the a/c on, driving at 75 mph and 25 deg outside temp.

I found Evan's made my Minivan run colder in the winter.
 

dremd

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May 31, 2007
Location
South Louisiana
TDI
06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
I got about 2~3 mpg better with high temp thermostat than I did both before and after I ran it. That said, I started getting coolant in my oil (blown head gasket) while I was using the higher temp thermostat, I totally don't know if my issue was caused by or related to the higher temps. I had 2 very loose head bolts (sub 10 ft/lb removal torque). I probably should have just re-torqued, but I tore the head off.
 

Franko6

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May 7, 2005
Location
Sw Missouri
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Jetta, 99, Silver`
Dremd,

Loose head bolts? That's scary. I bet you have a warped cylinder head.

The high temp idea is not good. We do think a thermostat that opens at around 90-95c is just fine. Certainly, if it opens 175, you will suffer fuel economy losses, and what is worse, all temperature gauges for about every VW starting in the AHU's LIES. It will be 190 on the dash, but not change from actual temps of 175 to 210. That, in my opinion, is the WORST idea, being lulled into complacency by a worthless temperature gauge. Then, you want to risk the upper boundary of the engine temps? NOT ME.

Just your case alone, dremd, is another part of the problem when you overheat. The head warps high in the middle and you have water blowing out and oil in the reservoir.

Retorquing loose head bolts will not cure a warped head. Neither will ARP head studs fix what is basically, a damaged cylinder head.

Dremd, now that your cylinder head is off, you can easily check for warp. A marginally warped head will bow between the manifold side head bolts and you can see the bridging between boltsby shining a light behind a straight edge.

A badly warped head will allow the camshaft to rock in the journals, when you clean off the oil from cam and cam saddles. The head will need the journals align bored to straighten the cam shaft journals. I don't know too many who do that, but we have the align boring tools.

When we build cylinder heads and blocks, we install a heat tab. The tab has a lead melt out in it's center that is gone at 230 degrees. You don't have to test the upper limits to warp an cylinder head. Regularly being above 200 degrees will do it.

The block will also warp. But it warps in the opposite direction as the head. The low place will be the webs between cylinder bores and can be checked with a machinist's block laid across the head bolts in line with cylinder webs between 1-2, 2-3, 3-4. If you see daylight, it's not flat.
 

dremd

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South Louisiana
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06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
Dremd,
Loose head bolts? That's scary. I bet you have a warped cylinder head.
.
I sent the head off to YOU in early 2015! I don’t know if you did mill the head, but said it wasn’t significantly warped. You replaced 2 valves, had some comments on head looking like it had high miles (true) sold me a cam and told me to use a machinist straight edge to check block for straightness. I got Starrett 380-24 24-Inch Steel Straight Edge https://www.amazon.com/dp/B0006J4GKK/ref=cm_sw_r_cp_api_i_QnkPCbFA0045F and I couldn’t get a piece of paper underneath it in any spot with all of the combinations that I could come up with, having the block still in car did limit it some, but I feel ok about it. I used ARP studs to bolt it down which you didn’t really like the idea of, but being a recovering MKIII Supra owner I insisted on.
That was 30,000 miles ago and no more coolant in oil according to Blackstone.

I haven’t driven the car much in the last 2 years due to the delight of EV’s, but every time I turn the key it runs as good as ever
 
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clove5

Well-known member
Joined
Dec 10, 2009
Location
Central Virginia
TDI
99.5 golf 1.9l, white, two door
I performed this mod and are monitoring temps through bluetooth dongle ams torque pro app.
I am seeing average temperatures 212f - 219f.


Reading this thread those temps appear normal.



I want to confirm with you guys this is ok numbers?
 

turbovan+tdi

Top Post Dawg
Joined
Mar 23, 2014
Location
Abbotsford, BC.
TDI
2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
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