Modified Thermostat for higher MPG's...

Growler · Jan 31, 2012

my mileage seems to be consistantly higher than the same period from a year ago. see my fuelly link in signature for all the data.

my heat inside my cabin is greatly improved, once it gets up to temp.

it seems to warm up a little faster due to both the higher temp stat, and the two grille vents being blocked, I still havent put on my lower grill block from my winter front. (lazy)

overall, I am well pleased. the thermostat has paid for itself already in saved fuel this winter.

josh8loop · Jan 31, 2012

Growler said:
my mileage seems to be consistantly higher than the same period from a year ago. see my fuelly link in signature for all the data.

my heat inside my cabin is greatly improved, once it gets up to temp.

it seems to warm up a little faster due to both the higher temp stat, and the two grille vents being blocked, I still havent put on my lower grill block from my winter front. (lazy)

overall, I am well pleased. the thermostat has paid for itself already in saved fuel this winter.

That is really great to hear! Thanks for the update

TheHolyCobra · Feb 2, 2012

What kind of coolant temps are people logging in VAGCOM with the higher temp thermostat? With my new 87* stat I see low ti mid 90s while cruising on the highway in the winter.

Aaron have you logged your car at all?

josh8loop · Feb 2, 2012

TheHolyCobra said:
What kind of coolant temps are people logging in VAGCOM with the higher temp thermostat? With my new 87* stat I see low ti mid 90s while cruising on the highway in the winter.

Aaron have you logged your car at all?

I've got 205-209 F here in Florida reported by ScanGageII if that helps any. That is approximately confirmed by my in line digital coolant temp probe.

Growler · Feb 2, 2012

i suppose I could log my coolant temps on a trip to work and back some time next week.

havent checked it, no.

Vekke · Feb 4, 2012

I just read the whole thread trough and did some search on termostats. Almost all newer cars have higher termostat highest stock were 105 celsius in opel and BMW models from 2006- those seem to were in petrol models though :/.

Highest stock diesel thermostats were that 92 celsius which is pretty common value.

It would help hugely to summarize this thead more in the first page if someone has the time and rights to do it. I will test this in my lupo 3L for sure because its freezing cold in winter even with full grill block and no intercooler :/. Also the fuel consumption is way too high for that car IMO.

Dieselducky · Feb 4, 2012

I'm sure the aluminum head is gonna love you for it

josh8loop · Feb 4, 2012

Vekke said:
I just read the whole thread trough and did some search on termostats. Almost all newer cars have higher termostat highest stock were 105 celsius in opel and BMW models from 2006- those seem to were in petrol models though :/.

Highest stock diesel thermostats were that 92 celsius which is pretty common value.

It would help hugely to summarize this thead more in the first page if someone has the time and rights to do it. I will test this in my lupo 3L for sure because its freezing cold in winter even with full grill block and no intercooler :/. Also the fuel consumption is way too high for that car IMO.

Done-I added a "Cliff Notes" version

alloutdoorsboy · Feb 6, 2012

On a side note, I have been getting a 97 passat ready for the Mrs to drive. The temp gauge on it doesn't work. Just hooked up a scan gauge II to find coolant temp is 162

Now to source a thermostat, local parts store says highest they have is 92C..

Growler · Feb 6, 2012

get a high temp one from an 87 GTI 8V 1.8L

any local auto parts store will have them cheap.

MikeMars · Feb 6, 2012

alloutdoorsboy said:
...The temp gauge on it doesn't work. Just hooked up a scan gauge II to find coolant temp is 162

Now to source a thermostat, local parts store says highest they have is 92C..

Often due to the temperature sender supplying a false reading (green, 4-pin, component about 1.5cm across) rather than the thermostat. But both components are pretty cheap, & the fix is DIYable. I'd recommend buying both.

josh8loop · Feb 6, 2012

MikeMars said:
Often due to the temperature sender supplying a false reading (green, 4-pin, component about 1.5cm across) rather than the thermostat. But both components are pretty cheap, & the fix is DIYable. I'd recommend buying both.

Like Mike said, buy both and get them done. You won't regret doing it. By the way, some times the thermostat housing gets brittle, and breaks. You may want to get a replacement for that aswell.

alloutdoorsboy · Feb 9, 2012

Will a faulty temp sender cause the ECM to call for more fuel hence reduce MPGs??

MikeMars · Feb 9, 2012

If it's particularly cold, I think it may do this

Growler · Feb 9, 2012

one more point of reference soon to be on the road.

this 2003 Wagon is being assembled with the higher temp MK2 Thermostat like what I have in my 2003 Wagon. altho this owner has a MUCH longer daily commute and should make much better mileage overall than I do.

link to thread of reassembly.
http://forums.tdiclub.com/showthread.php?t=342408

alloutdoorsboy · Feb 9, 2012

MikeMars said:
If it's particularly cold, I think it may do this

Mike, seems like mine is reading about 30f low, it said yesterday that it was 20f at start up where it was about 50f outside temp. Im going to change the sensor anyways but thought this could be one more thing for folks to look for who have bad MPGs....

SD26 · Feb 9, 2012

alloutdoorsboy said:
Will a faulty temp sender cause the ECM to call for more fuel hence reduce MPGs??

Ok, this leads me to ask a question. And I ask it in relationship to my experience with the 7.3 Power Strokes that I had.

Does the TDI ECM use coolant temperature in its calculations for fueling and fuel timing?

The 7.3 Power Strokes do NOT use coolant temperature for the ECM values. The 7.3PSD used oil temperature to make its ECM decisions.

Can someone answer a question too? I now have an A4 to go along with my A3. I have a Scanguage II. Seems as though the coolant temperatures that I was used to seeing with my A3 are different than what my A4 has. Did the A4 have a thermostat with a lower opening temperature? (Lots of pages in this thread, and I'm hoping for a possible answer. I used the 203* thermostat in my two 7.3PSD's. This thread is very interesting to me as a result of my previous diesel experiences.)

josh8loop · Feb 9, 2012

SD26 said:
Ok, this leads me to ask a question. And I ask it in relationship to my experience with the 7.3 Power Strokes that I had.

Does the TDI ECM use coolant temperature in its calculations for fueling and fuel timing?

The 7.3 Power Strokes do NOT use coolant temperature for the ECM values. The 7.3PSD used oil temperature to make its ECM decisions.

Can someone answer a question too? I now have an A4 to go along with my A3. I have a Scanguage II. Seems as though the coolant temperatures that I was used to seeing with my A3 are different than what my A4 has. Did the A4 have a thermostat with a lower opening temperature? (Lots of pages in this thread, and I'm hoping for a possible answer. I used the 203* thermostat in my two 7.3PSD's. This thread is very interesting to me as a result of my previous diesel experiences.)

To my knowlege the A4 was designed to have an operating temperature of 87 Deg C(188.6 Deg F). Not sure what the A3 was set up for.

SD26 · Feb 10, 2012

josh8loop said:
To my knowlege the A4 was designed to have an operating temperature of 87 Deg C(188.6 Deg F). Not sure what the A3 was set up for.

Thanks!

Might not even be "designed" to have that low of an operating temperature, but NOx emissions requirements made it that the lower temperature t-stat kept those emissions within specs... That's how the original 7.3PSD's got bumped down to their lower temperature t-stat: NOx emissions requirements over better MPG and less emissions of other elements. Don't know if that was touched on in this thread, but maybe it is a similar situation for diesel cars too in the US.

josh8loop · Feb 12, 2012

SD26 said:
Thanks!

Might not even be "designed" to have that low of an operating temperature, but NOx emissions requirements made it that the lower temperature t-stat kept those emissions within specs... That's how the original 7.3PSD's got bumped down to their lower temperature t-stat: NOx emissions requirements over better MPG and less emissions of other elements. Don't know if that was touched on in this thread, but maybe it is a similar situation for diesel cars too in the US.

I doubt it would make a difference in NOx, but I don't have anything to back that up. It certainly isn't out of the realm of possibility though. For folks in areas that still do vehicle testing, you could try the "Hybrid" T-stat and see if you pass with it installed. If you don't pass, just switch back to the other one.

alloutdoorsboy · Feb 16, 2012

OK so Im going to put in a 92 thermostat this weekend and wanted to change over to Propylene glycol coolant. I was going to get Evans but now realize its not available locally so I have run out of time to order it. Napa has 100% Propylene glycol for $15 a gallon, would you guys run this????

SD26 · Feb 16, 2012

Parts ordered to build a hybrid tstat...

alloutdoorsboy said:
OK so Im going to put in a 92 thermostat this weekend and wanted to change over to Propylene glycol coolant. I was going to get Evans but now realize its not available locally so I have run out of time to order it. Napa has 100% Propylene glycol for $15 a gallon, would you guys run this????

Well...

PG is PG. But Evans is not simply 100% PG. I generally use Evans NPG+ in my street applications.

I have used RV anti-freeze in engine applications myself for racing. It's PG, and it's about $6 a gallon. What you're comfortable with would have to be what you're comfortable with in risk and the like.

I think the best price and most reasonable shipping cost I've found on Evans has been through Aircraft Spruce. Haven't found it locally.

alloutdoorsboy · Feb 16, 2012

OK so I went to Napa and what they had was Sierra which is PG based but on the list of contents it includes water even though you are supposed to dilute it. I ordered some Evans through ebay for $42 gallon including shipping for 4 gallons since I have 2 cars to do.....

josh8loop · Feb 16, 2012

SD26 said:
Parts ordered to build a hybrid tstat...

Well...

PG is PG. But Evans is not simply 100% PG. I generally use Evans NPG+ in my street applications.

I have used RV anti-freeze in engine applications myself for racing. It's PG, and it's about $6 a gallon. What you're comfortable with would have to be what you're comfortable with in risk and the like.

I think the best price and most reasonable shipping cost I've found on Evans has been through Aircraft Spruce. Haven't found it locally.

Dave,

Do you have a SGII or equivalent so you can monitor your temps during the "Hybrid" T-stat experimentation? Certainly recommended

It's always nice to have direct feedback on temps for a while until you are satisfied you have consistancy like I do now. FWIW

SD26 · Feb 16, 2012

josh8loop said:
Dave,

Do you have a SGII or equivalent so you can monitor your temps during the "Hybrid" T-stat experimentation? Certainly recommended It's always nice to have direct feedback on temps for a while until you are satisfied you have consistancy like I do now. FWIW

I do, Josh!

Just for some comparison, my A3 does indicate a warmer temperature than my new uo me A4. Seems like with our weather lately, less than 180f is the norm vs nearly 190f on the A3.

josh8loop · Feb 16, 2012

SD26 said:
I do, Josh!

Just for some comparison, my A3 does indicate a warmer temperature than my new uo me A4. Seems like with our weather lately, less than 180f is the norm vs nearly 190f on the A3.

Good, glad to hear you have a temp monitoring device. Just out of curiosity, what are the specifics/history on the A4 you have? Any EGR mods or anything else? It's manual right?

SD26 · Feb 17, 2012

josh8loop said:
Good, glad to hear you have a temp monitoring device. Just out of curiosity, what are the specifics/history on the A4 you have? Any EGR mods or anything else? It's manual right?

Yeah, nice and simple: manual Jetta wagon, no mods. A board member's former car.

josh8loop · Feb 17, 2012

SD26 said:
Yeah, nice and simple: manual Jetta wagon, no mods. A board member's car.

How many miles on it? Sounds like you may be able to provide some MPG feedback before and after the change that will help to determine if this increases MPG's like I think it does.

SD26 · Feb 17, 2012

josh8loop said:
How many miles on it? Sounds like you may be able to provide some MPG feedback before and after the change that will help to determine if this increases MPG's like I think it does.

Engine has about 124k on it. I only have a couple tanks for data as I just got it. So, I won't really have a hard number on anything previous to its history with my driving.

I know that with the 203F t-stat on 7.3PSD's, that was good for a half MPG. So, this makes a lot of sense to me.

If I can prove this to myself as being good in my TDI, I might do it also in the A3 Jetta. I've got thousands of miles of hard data there, I would just need to figure out the thermostat.

Frankencar · Feb 17, 2012

SD26 said:
I might do it also in the A3 Jetta. I've got thousands of miles of hard data there, I would just need to figure out the thermostat.

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.

Modified Thermostat for higher MPG's...

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