Modified Thermostat for higher MPG's...

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
DF,

I found that the coolant reservoir was about 2 maybe 3 degrees cooler than the outlet flange. Pretty close IMO. Are you running radiator block offs? I just blocked mine off this evening to see if I can get a little higher temps with my 195 deg T-stat before experimenting w/ the other one.
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
Yes, I am, pipe insulation. I really don't think it makes much difference, to tell you the truth. I actually forgot about it til you mentioned it.

Maybe using cardboard up against the radiator might work, but that would block airflow. I'd rather not block airflow.

I'm sure inside the block the coolant is 190F, at least. So, again, if we could get 200-205F, at least, in the tank, that would be great.

Remember, Evans was talking about raising the temp 20F more than stock. So, that puts the TDI at 210F.

Also, those ARP 2000 studs for the TDI are about $199, but Kerma may have them for $159. They were on sale. I'll have to check.

df
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
Josh,

Everything going o.k.?

I just ordered the ARP stud kit from Kerma. When I get time to install them, I will. Hard to find a time when the TDI isn't being driven. :>)
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
DF,

Everything is fine, thanks. I have been doing some minor maintenance activities on the TDI as of late that I wanted to get straightened out. Namely I am replaceing the fuel lines in the engine compartment. I have installed a small clear teflon section so that I can see air bubbles in the fuel lines. It is looking really nice. I found some fuel line fittings(quick disconnect Elbows) from a 1.8T Jetta and used weather head(cloth covered) 5/16 fuel line. It looks really nice, and looks like it was meant to be there. I have also installed some engine cover pop fasteners-it is really nice to quickly pop the cover off when needed.


I was experimenting with partially blocking the radiator to see how the engine operates at elevated temperatures. I found out my T-stat I have now(195) doesn't seem to be functioning properly. I was able to get it to about 200-205 degrees with the blockoff. I want to be carefull since my transmission is cooled by the engine coolant, and I am not sure how it will respond to the 205 degrees.
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
What did you use to block off the radiator.... cardboard? How did you install it...?

I'd like to get rid of my pipe insulation and go with another solution.
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
DF,

I used rubber matting from an old ergonomic floor standing mat I had laying around. I cut it to approximately the width of the radiator, and slid it up under the front valence directly contacting the front of the radiator. Have you seen the Ford commercial on TV that shows a car with moveable louvers in front of the radiator-I think it is the Fiesta. Neat for sure.
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
O.k., and how does it stay against the radiator and aren't you afraid it may melt?
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
DF,

The foam is about 2" thick, so when you pass it through the lower valence and start vertically in front of the radiator it gets held in place between the radiator and a horizontal cross member about half way up. I'm not concerned with meltage-this is the same stuff I remade my engine cover sound deadening with. It has been fine for a month or so on top of the engine.

The only bad thing about the radiator block is that any air that would need to be passed through for the A/C condenser would be blocked which could cause higher than normal A/C pressures. Also, you are gambling that the unblocked portion will be able to sufficiently reject enough heat to maintain engine temperatures. The weather here has been cool one day, and hot the next, so that makes it a bit tricky for me. I mainly used it to see if my mileage went up, and to see it the T-stat was working properly. No numbers yet.
 
Last edited:

Honeydew

Top Post Dawg
Joined
Nov 28, 2006
Location
Florida
TDI
13 Passat DSG
Josh, give me a call and come by the shop. I'll loan you my vag-com plus an old laptop to run it if you'd like. I forgot about the laptop when we spoke last week, I was driving a rental suburban in Alabama during a downpour trying to follow someone to our destination.
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
HoneyDew,

Will do, greatly appreciated. Nice talking the other day by the way.
 

dezeljunky

Veteran Member
Joined
Sep 18, 2010
Location
Richmond, BC
TDI
2003 Golf GLS TDI Silver 5spd
What does the extra spring on the TDI thermostat do compared to the regular gasser thermostat? Sorry if it's been asked already.
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
Diezeljunky,

That spring is there to allow the rear disc to seat in the bypass opening in the block while still allowing the thermostat to continue opening. If it was a single piece, the disc would seat and the thermostsat opening stroke would be limited.
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
ARP head studs are in and o.k. Got it up to operating temp and ran it HARD up to 80 mph in gears 1-4 and just put it in 5th and cruised home. Got back, popped the hood and nothing leaking. Everything looked and seemed fine. :>)
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
DF,

Good, glad to hear it went well. Let us know how the mileage side of things goes.
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
Josh,

Just filled up, and there was no increase of mpg with the ARP headstuds installed.

I was within .07 mpg of my prevoius fill-up with the stock headbolts.

I guess if someone had a gasket leaking coolant, their mpg would suffer over time. Installing the ARP's would give better sealing and hence restore their mpg.

There's no way, imo, taking a healthy engine such as mine, and installing ARP headstuds and getting higher mpg. Not even ARP would make such a claim, lol!
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
DF,

Thanks for the update on the ARP studs. I'm sure you are glad that they are installed at least.
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
All,

I ended up installing the modified thermostat yesterday, and doing some testing. I used a friends Vag Com to monitor temperatures during the test. The temperatures with the modified T-stat reached 103 Deg C, which is about 217 Deg F, and was still climbing. This concerned me greatly, and I ended the test. Before I installed the modded T stat I had known that the rear bypass section of it was uneven by about 15 thousandths. The press tool I had made was not quite square as I don't have a lathe here. I am thinking this made the difference, and plan on trying to square up my tool, and try it again. The modded T-stat should keep it around 94 Deg C(205 Deg F)
 
Last edited:

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
Josh,

Yes, I'm glad to have the ARP's installed: Peace of mind..., lol!

Wow, 217+F! Too bad. With Evans HDTC, 210F would be perfect, imo.

Thanks and keep us posted,
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
Fellas,

I am in the process of having my press tool aquared up a bit at work. Should be done in the next few days. This will allow me to re-press the T-stat together squarely this time instead of having a slight wobble to the bypass section. I will probably also pick up a new T-stat O ring even though the one in their now is only a few mths old. I also need to source the 4mm x 32mm "O" rings for the coolant line quick disconnect fitting on the top & bottom of the radiator and replace them as preventative maintenance. With any luck I should be able to test the modified T-stat again in the next couple weeks. On thing I noticed as was expected at the higher coolant temps, the coolant system was indeed pressurized higher than normal by the feel of the radiator hoses.
 

Ski in NC

Top Post Dawg
Joined
Jul 7, 2008
Location
Wilmington, NC USA
TDI
2001 Jetta ALH 5sp stock
After breaking into cooling system, air gets into system, hides in pockets. and some gets dissolved into the coolant. When it heats up, solubility goes down and the coolant off-gasses. This raises pressure in system and hoses get hard.

What I do on any cooling system I do major work on, is to run system with no cap on and let engine run up to full temp (on tdi, that means fans cycle on). This tends to expel non-condensible gasses through the bottle cap. Do this and then pressure does not get so high in normal thermal cycles.
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
Ski,

Good point, especially when performing these non traditional tests with higher temps. I ended up using a vacuum source to help with the refill. Seemed to work out nicely both times I used it. I just wish there was a better way to drain coolant other than removing the lower oil cooler coolant line. That makes for a very messy drain, and I end up loosing coolant inventory. Wish there was a modification for a quick drain on that lower coolant pipe like the one on the lower radiator.
 

Tom W.

Veteran Member
Joined
Dec 9, 2005
Location
Raleigh, NC
TDI
mash-up GettaTDI150, 1986 Jetta Delux D, 2005 Passat TDI sedan
thermal efficiency

Generally, the higher the temperature, the higher the thermal efficiency of the engine( more HP, better MPG). Remember Smokey Yunick's Adiabatic engine?
Some are using waterless coolent to boost their temps. http://www.evanscooling.com/
I don't know if the coolent is compatible w 1.9 TDI or not- I use this in my Jetta 1.6 diesel and my Chevy. I use it because it eliminates all possibility of corrosion, and because there is no longer pressure in the system- which means if I have a leaky hose, I don't loose pressurized coolent- the coolent just slowly drips out. This stuff has actually saved me three times from overheating.
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
Ah, Tom, you're the one using the EVANS!

How did you drain out all of the G12? I understand there can be no more than 3% water with the Evans. Did you use the Evans pre-treatment?

Thanks,
 

Tom W.

Veteran Member
Joined
Dec 9, 2005
Location
Raleigh, NC
TDI
mash-up GettaTDI150, 1986 Jetta Delux D, 2005 Passat TDI sedan
Evans

I'm not using Evans in the Getta, but I have been using Evans in a bunch of my vehicles- started using it in 1996, in a new chevy Astro.
I also converted my 1.6 diesel Jetta in 2001, and several other vehicles. Still own the Astro and 1.6 Jetta, and Evans has quite literally saved both vehicles from the scrap heap by preventing catastrophic cooling system failure.

I don't know if it is compatible with my 1.9TDI Getta. I didn't convert Getta because I wasn't sure I wanted to keep her. Still don't know If I'll keep her. (Getta's a lot of fun, but it's a bit too much car for me-I like to drive slow-my wife says I like to "putter along" )

On one hand, I love Evans, because it works exactly as advertised- zero pressure, zero corrosion, zero maintenence, and I never have to worry about overheating again.

Downside of Evans: It is REALLY expensive, I cannot get it locally, so I have to pay/wait for shipping , and probably the # 1 problem with the stuff is that it is a real PITA/impossible to get all of the old coolant out of your system. I would not spend the time/effort to convert a vehicle, unless I was planning on keeping the vehicle forever(but that's just me).

What I did to remove the old coolant/ convert to Evans: Park the vehicle on a steep decline(pointing down hill), removed the upper and lower radiator hoses as well as the thermostat, got my two burly boys to help me rock the vehicle, and then rigged an air pressure hose to the engine block top to blow out as much coolant as possible. I did not pop out the freeze plugs in the block, because I couldn't figure out how to do that without pulling the engine (space was too tight).
I then filled w Evans, and drove with the expansion tank cap/radiator cap loose. I think it took abt 3 months to actually boil off the water that remained in the system. You know when the water is all gone, because you can tighten the expansion tank cap/radiator cap, drive till up to operating temp, and then squeeeeeze the upper hose- zero pressure!

Evans has some new stuff for flushing/pretreatment - probably what I will do when I convert wife's Nissan.

I run all my vehicles with stock thermostats,- I know from personal experience that you can run Evans way past the temp gauge red line safely, but I never did it intentionally. Both times it was because I had lost a water pump, and was far, far away from a service station.
 
Last edited:

Tom W.

Veteran Member
Joined
Dec 9, 2005
Location
Raleigh, NC
TDI
mash-up GettaTDI150, 1986 Jetta Delux D, 2005 Passat TDI sedan
Running at higher temperatures

This has me thinking- did some more research. Smokey Yunick's Adiabiatic engine. http://schou.dk/hvce/ http://www.rexresearch.com/yunick/yunick.htm
I think we can apply some lessons here:
Smokey converted several normal Chrysler and Chevy engines, so we know that normal engines can be run at extreme temperatures safely. The fuel/air mixture was 1,508F when compressed, just before combustion. I think it is safe to assume Smokeys engine temperatures were far beyond anything anyone here has considered, and these engines apparently ran just fine.

I did read he was using jet engine oil for lubrication- Mobil Jet engine oil has an effective operating range of -40F to 400F. 400F? Wow!

What would happen to thermal efficiency by bumping the coolant and oil temp to 300F from 190F? Our little TDI's are already so thermally efficient, I am not sure you could get up to these temperatures.
 

dieselfuel

Veteran Member
Joined
Dec 28, 2008
Location
ohio
TDI
2003 Jetta TDI
Tom,

The only thing that concerns me is, the headgasket.

Coolant temp 300F? I don't think I'd want to go over 230F.

I'll read that link when I've got more time.
 
Last edited:

Tom W.

Veteran Member
Joined
Dec 9, 2005
Location
Raleigh, NC
TDI
mash-up GettaTDI150, 1986 Jetta Delux D, 2005 Passat TDI sedan
I'm not so sure the headgasket would be an issue, as they are metal. Dosen't seem to have been a problem for Smokey. Hmmmm. One more thing to ponder.
Here's another thing- Smokey was using gasoline engines- which have a pre-detonation issue at higher temps. Diesels don't have that issue. Wonder if there is any more info on how Smokey handled the thermal stress on the engine?
 

Ski in NC

Top Post Dawg
Joined
Jul 7, 2008
Location
Wilmington, NC USA
TDI
2001 Jetta ALH 5sp stock
Patents last a maximum of 20yrs so it is probably expired.

Years ago I did a little research on "adiabatic" engines. Of course none are truly adiabiatic, as even without a cooling system there is heat transfer between process fluid and metal.

What seemed to be concluded (and memory may be a little foggy on this) is that thermal efficiency was not really increased much, but the amount of heat lost through exhaust increased to cover what normally was rejected in the cooling system.

Most of the design work involved keeping moving parts from burning up. That problem was solved on conventional designs long ago.
 
Last edited:

Tom W.

Veteran Member
Joined
Dec 9, 2005
Location
Raleigh, NC
TDI
mash-up GettaTDI150, 1986 Jetta Delux D, 2005 Passat TDI sedan
So, how much of an improvement can be achieved in raising coolant temps?
Auburn University http://www.pavetrack.com/PAVE/Evans%20NPG%20+%20Type%20II%20Fuel%20Economy%20Test%20Report.pdf has reported that increasing the thermostat from 190F to 215F creates a 3% MPG improvement in commercial diesel engines. Wonder what it would do for our TDI?
If you wanted to run a 215F thermostat in your TDI, you would need to figure out a way to override the cooling fans coming on until 230F.

Evans has tested both gas and diesel engines, and ther research indicates that most engines can be operated at a sustained engine temp around 260F, with spikes up to 300F. The only problem they have found is that some valve springs might loose some of their spring pressure at temperatures of 260F and higher. So, if you are planning on operating your engine above 260F for sustained periods of time, you would probably want to upgrade your valve springs.
Bottom line, operating with a 215F thermostat is not that big a deal, as long as you are using a waterless coolant.
 
Last edited:
Top