Modified Thermostat for higher MPG's...

Originally Posted by josh8loop View Post
Just for informational purposes, if someone wanted to replace their thermostat and didn't want to experiment with the "Hybrid" construction method, and good second choice might be:

http://www.autopartswarehouse.com/sk...&+Drivetrain


That would give you 197.6 deg F (92 Deg C). This is the highest direct fit type that I have found for the ALH engine. Most replacement T-stats from Wahler and other OEM brands seem to only go to 87 Deg C(188.6 Deg F) The Behr unit mentioned above seems to be of a good sturdy construction, and may possibly out last Stant types FWIW.

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I installed one of these MK2 high temp thermostats today. VCDS says on a 20 mile loop to work & back, got up to 93.2C so it seems to be working properly.

THanks for the idea guys. Ill keep an eye on my mileage. I am hoping to improve my poor mileage.

aaron

I'm thinking that the modified 'stat is responsible for a higher mpg figure during these colder temps recently (mornings in the 30's, daytime in the 40's). I believe I'm up about 2 mpg compared to last year at this time, when I was running the stock t-stat.

Aaron,

Thanks for letting us know that Mk2 t-stat will work in our MkIV's.

Why do you think you were/are getting poor mpg...., faulty t-stat...?

ya, my heat has never been great in this car, and with my mileage this summer, I figured with the results you guys were seeing with these hybrid & higher temp thermostats, that it was worth a shot.

That's because spark knock will kill a gas engine, diesels are totally differen No fuel is in the cylinder until it's injected, so that can be no premature ignition. Second, what they are trying to prevent in the gas engine, spontaneous combustion, is what you want in a diesel...hence the whole idea of a hotter cylinder.

dieselfuel said:

I'm fine with my hybrid in the cooler months. Late next spring, I'll try the other hybrid to see what temps I get.

What I need to know is, does high coolant temps and advanced timing harm a TDi engine.

And, does a higher coolant temp retard timing, or is timing taken from fuel temp...?

I was talking to a guy who mods gaasers (Mustangs, Corvettes). He mentioned that he uses a lower temp t-stat and gives the engine lots of timing. When I inquired why he uses a lower temp t-stat, he said that high coolant temps with lots of timing will kill an engine. He has an 09 vette and uses a 160F t-stat (stock, I believe, is 108-190F).

Anyhow, if the high temp is alright with the ALH and a performance tune, I'd like to be able to fool the ECU into not cutting back (retarding) timing due to high coolant and/or high fuel temp.

Later on, I'll check my fuel temp, I can't remember what temp I was getting after I installed the hybrid and was recording coolant temps of 230+F.

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Growler said:

I installed one of these MK2 high temp thermostats today. VCDS says on a 20 mile loop to work & back, got up to 93.2C so it seems to be working properly.

THanks for the idea guys. Ill keep an eye on my mileage. I am hoping to improve my poor mileage.

aaron

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Aaron, do you have a part # or a link that works for this thermostat? I need a new one for the B4 and want to go with a higher temp one too, but I can't find the one that you ended up using

A few weeks ago I installed a Stant stat from autozone, IIRC it was labeled 92*C. This stat is what their computer showed for my car. I wonder if this is the same stat Growler got. With this new stat Scangauge water temp has been 200*F +/- 2*F.

Jason,

Just go to the auto parts store. tell them you want the high temperature thermostat for a 1986 golf 1.8L gasoline engine. and a new o-ring for the same.

OI got mine from O'Reiley. it was $8 or some low price. doesnt matter to me, its in now and I bought it a month ago.

should be available for cheap at ANY parts store.

good info, post like theses are what makes this place great.

Growler said:

Jason,

Just go to the auto parts store. tell them you want the high temperature thermostat for a 1986 golf 1.8L gasoline engine. and a new o-ring for the same.

OI got mine from O'Reiley. it was $8 or some low price. doesnt matter to me, its in now and I bought it a month ago.

should be available for cheap at ANY parts store.

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monitoring SOI

After reading this I decided to post my observations:

Originally Posted by dieselfuel
I'm fine with my hybrid in the cooler months. Late next spring, I'll try the other hybrid to see what temps I get.

What I need to know is, does high coolant temps and advanced timing harm a TDi engine.

And, does a higher coolant temp retard timing, or is timing taken from fuel temp...?

I was talking to a guy who mods gaasers (Mustangs, Corvettes). He mentioned that he uses a lower temp t-stat and gives the engine lots of timing. When I inquired why he uses a lower temp t-stat, he said that high coolant temps with lots of timing will kill an engine. He has an 09 vette and uses a 160F t-stat (stock, I believe, is 108-190F).

Anyhow, if the high temp is alright with the ALH and a performance tune, I'd like to be able to fool the ECU into not cutting back (retarding) timing due to high coolant and/or high fuel temp.

Later on, I'll check my fuel temp, I can't remember what temp I was getting after I installed the hybrid and was recording coolant temps of 230+F.

I replaced my stat with a Stant "superstat" don't have the part # with me.

It was a 195° F and the superstats have a larger heat motor than the other Stants.

It runs 204 -207°.

To monitor Start Of Injection on an ALH with a scan gauge use the IGN function.

I also found that even with the new stat, the start of injection seems to stay advanced until the IAT climbs to over 90°.

I have an RC5 tune. I don't know if that makes a difference.

So you are saying, the timing advance is based on IAT not water temp, sounds reasonable.

If so, it's nice confirmation (fixed, sorry). Expounding: I agree that there is an emissions (NOx) angle to pull-back timing, but as far as input temperatures are concerned, NOx responds primarily and directly to intake air temperature, only weakly and indirectly so to coolant temp. If the timing is significantly retarded, it can also increase coolant temps and therefore create an unwanted positive feedback.

TDIMeister said:

If so, it's nice confirmation.

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Linky no worky

Growler said:

I installed one of these MK2 high temp thermostats today. VCDS says on a 20 mile loop to work & back, got up to 93.2C so it seems to be working properly.

THanks for the idea guys. Ill keep an eye on my mileage. I am hoping to improve my poor mileage.

aaron

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Aaron,

Thanks for the update on this. It looks like my link no longer works for some reason. Did you get yours from Autopartswarehouse, and if so, what is the part number so I can update my original post about it. Thanks!

..

I did not, I purchased mine from O'Reileys local auto parts store.

went to counter, asked for a high temp thermostat and o-ring for a 1986 Golf 1.8L 8V Gasser. got a 92* C thermostat.

Commonly available at any parts store. Cheap.

pretty easy and no website required, no shipping, just walk in, ask, and walk out.

JPD and TDIM,

Just what I thought, since the ambient temps have cooled off. Back in the mid summer/early fall, I was experiencing "heat soak". I don't have the same experience now since the cooler ambient temps. My TDI ran awesome yesterday (40F) with LOTS of power in the whole operating range.

Still may go to a "cooler" t-stat in the summer, though. I'd rather be in the 205-210F range. 230+F, even with the Evans HDTC, makes me a "little" nervous on hot days.

I would not have any concerns in summer if you're using the Evans coolant and your system is completely water-free. The BP of the coolant is 375°F, which is more than 100 degrees higher than pressurized ethylene glycol/water. It's a combination made in heaven, IMO.

Any idea on the extra viscosity of Evans affecting the water pump? Also, what is the difference between Evans and just running 100% coolant? I figure 100% coolant would be the same.

Evan's coolant (propylene glycol) and regular coolant (ethylene glycol) are completely different chemicals with different properties. Using ethylene glycol straight does not give sufficient protection from freezing at cold temperature, since its freezing point is only about -12°C. Also, ethylene glycol by itself has a low specific heat capacity (about 60% that of water), so even though it has a high boiling point, its ability to STORE HEAT is poor. Adding water increases the specific heat capacity and up to a certain point (~70% EG) decreases the freezing point.

On the other hand, propylene glycol does not need any water to reduce the freezing point, being -59°C when pure. The specific heat capacity of PG is slightly higher than EG but is still less than water. However - and this gets really complicated - both PG and EG are better than water at promoting nucleate boiling rather than film boiling, which is a desirable property for heat transfer effectiveness, especially in hot spots.

The higher viscosity of PG will increase pumping work; on the other hand, a lower vis product is available from Evans (NPG-R). The various Evans products are, judging from an MSDS found, just blends of anhydrous PG and EG with corrosion/foam inhibitors.

Edit: BTW - NPG-R can be used in pressurized systems so no change of the radiator cap is necessary. BP at 7 PSI is 400°F but is not suitable for cold climates (FP is -10°F).

has anyone addressed the spring tension on the factory stat vs aftermarket brands? i put in an aftermarket 195 and the engine never ran that warm, always around 170 to 180 and uphill maybe 195. comparing side by side the factory spring is much beefier and aftermarket real weak by comparison. so i deduced its the flow of the water forcing the stat open, suction on one side and pressure on the other opening it up. the factory stat wont do that probably as the spring is stiffer when its new. its not that the pellet could be bad as so much the spring is weak on factory stat when old. what i did was simply leave in the factory stat that never got much above 160 or 170 and installed a stat in the upper hose rated at 195 and that seamed to do it pretty nice. now engine maintains 195 unless its super cold out and i have the heater on and i am going downhill. then it cools off. but much better than before. does that help?

Growler said:

I did not, I purchased mine from O'Reileys local auto parts store.

went to counter, asked for a high temp thermostat and o-ring for a 1986 Golf 1.8L 8V Gasser. got a 92* C thermostat.

Commonly available at any parts store. Cheap.

pretty easy and no website required, no shipping, just walk in, ask, and walk out.

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Gotcha, thanks!

I think the higher temp thermostat is working.

I am about 3-4 mpg higher than my mileage at the same timeframe a year ago looking at my fuelly data. if this keeps up, I will be very happy with this low dollar mod.

Growler said:

I think the higher temp thermostat is working.

I am about 3-4 mpg higher than my mileage at the same timeframe a year ago looking at my fuelly data. if this keeps up, I will be very happy with this low dollar mod.

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That's great to hear! Mimics my findings of a few MPG more. I'm now at right around 60 MPG in town. For some reason my Hwy(doing 68 MPH) MPG is worse. Probably speed related.

Does the mk2 thermostat have the rear bypass section attached like the OEM style TDI T-stats?

josh8loop said:

Does the mk2 thermostat have the rear bypass section attached like the OEM style TDI T-stats?

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Yes

92° Thermostat Info

Frankencar said:

Yes

92° Thermostat Info

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Wow, great information and confirmation on the bypass section. Why haven't we heard from you before on this subject? Wonder if there is an application for a mark 2 thermostat that is set up for 94 or 96 Deg C? Even if it was for a gasoline engine. As long as it has the correct dimensions and all it should work fine.

..

josh8loop said:

Wow, great information and confirmation on the bypass section. Why haven't we heard from you before on this subject? Wonder if there is an application for a mark 2 thermostat that is set up for 94 or 96 Deg C? Even if it was for a gasoline engine. As long as it has the correct dimensions and all it should work fine.

..

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Not sure how I missed this thread - some great discussion going on here. I installed mine because I was annoyed with how cold it was running. It still takes all of 15 miles to get up to 185° on my way to work in the morning, but it would never get there on the original thermostat that I believe was bad. The AHU sure does like to run cold when it's only pushing around a 2420 lb car. I am quite happy with the 92° thermostat because the heater finally works, and the MPG is not bad.

I am also unaware of a drop in thermostat higher than 92°, but it appears after reading this thread that it's not a problem to assemble one.

Frankencar said:

Not sure how I missed this thread - some great discussion going on here. I installed mine because I was annoyed with how cold it was running. It still takes all of 15 miles to get up to 185° on my way to work in the morning, but it would never get there on the original thermostat that I believe was bad. The AHU sure does like to run cold when it's only pushing around a 2420 lb car. I am quite happy with the 92° thermostat because the heater finally works, and the MPG is not bad.
I am also unaware of a drop in thermostat higher than 92°, but it appears after reading this thread that it's not a problem to assemble one.

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Cool, glad to see you around!

if the concern is about high oil temps why not just put a pd larger oil cooler in too?

shaunsummer said:

if the concern is about high oil temps why not just put a pd larger oil cooler in too?

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From my personal experience and from visual inspection of cam related and crankshaft related components on my car after running a higer temp T-stat for the past year and a half or so(15k plus miles) I have absolutely no concern of oil temperature issues with the stock coolant/oil heat exchanger FWIW. Not to say I wouldn't install it for other reasons if I had one at my disposal. Maybe others who have experimented with these higher temps would care to comment too.

Any updates from the guys experimenting with this type of setup? Higher winter coolant temps? Faster warmup times? Mechanical issues related to the higher temps? Fuel economy improvements?