Modified Thermostat for higher MPG's...

dieselfuel

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Can the fan temp operating be changed with the VDCS? Otherwise, a resistor would have to be used.

3% isn't all that great. But, the could be other hidden savings, like possibly, never having to replace your heater core, or your radiator. I understand the dash has to be removed to replace the heater core (what b***sh$%!).
 

GoFaster

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I know it's already been stated in this thread, but don't forget the effect of high temperatures like that on the engine oil ...

High temperature reduces the absolute viscosity, which reduces film thickness. In engines that are apparently sensitive to the viscosity (like the P-D's, which appear to be on the hairy edge with engine oils in the normal viscosity and temperature range), this COULD send it to the wrong side of that hairy edge.

In some applications, I'd be concerned about the temperature of the pistons, too.
 

Tom W.

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As far as 3% fuel savings, I'm guessing a TDI might do better than the big rig diesels- so many other factors, including mass, wind resistance, etc. in our favor. I hadn't thought of it, but Dieselfuel is right- running a zero pressure (waterless) cooling system means no heater core blow outs.

I know my fuel mileage on my 1.6 IDI spikes up on really hot summer days compared to winter mileage. In the winter, the best I've ever done is 46MPG. In summer, I get at least 55MPG when the temperature is over 85F over the exact same long distance route(I've often gotten over 60MPG) How much of that MPG increase is due to higher operating temps, and how much is from other factors,(warm air is less dense, hense less drag, tires are hotter/higher pressures=lower rolling resistance, etc) I don't know.

Regarding oil temperatures:
All oils have a specific continous duty operating range temperature stated by the manufacturer. For example, Mobil synthetics http://www.mobil.com/australia-english/lcw/audiences/synthetic_v_mineral.asp are designed to be able to run continuously at 356F (180C). Since engine oil temperatures almost always stay within 20F of the coolant, running our coolant at 215F, 230F, or even higher, should not affect a properly rated synthetic lubricant.
 
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dieselfuel

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Brian,

I don't tow with my TDI, but iirc, someone here mentioned who does, stated their oil temp never got above 265F. Also, I think they stated their coolant temp never got over 225F.
I notice you have a bike. Do you tow it with your TDI? Have you ever recorded the oil and coolant temps? I'd be interested what they were.
 

Tom W.

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Ok, I got a 215F thermostat heat engine. These are custom made for Evans by (I think) Stant. Evans builds thermostats for their own research. Evans says the only problem they have run into with using a 215F thermostat is that you have to figure out a way to keep the cooling fan from coming on until 230F. They typically wire in a resistor into the fan temp sensor- just like Dieselfuel suggested.

I'm comparing it to the heat engine in a standard thermostat and it is dimensionally EXACTLY the same size, so it would be pretty easy to swap it into an existing TDI thermostat, for those who want to "build their own"

The rep at Evans indicated that you may be able to buy one for $15- The guy I talked to is David Wright- ph#1-610-323-3114 -he's technical sales manager in the performance dept.
Word of caution: Evans has these custom made, they currently have some in stock for their own projects, this is a custom part with limited quantity/availability.

Lets start heating things up!
 
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dieselfuel

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Good info, Tom, good info! I'll be calling Evans and see if I can purchase one.

Now, we need to see if the vag-com can adjust the temp at which the fan turns on.

Would blocking the radiator give the same affect? Assuming ou could get to 210-215F? What about just disconneting the fan altogether? (Again, I never tow with my TDI).

A few things to ponder, I guess....
 

josh8loop

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DF,

In the Bentley service manual in section 19-8, they mention the radiator fan thermo-switch operating temps:

Stage 1
Switch on .......................197-206 deg F(92-97 DegC)
Switch off........................183-195 deg F(84-91 Deg C)

Stage 2
Switch on ........................210-221 Deg F(99-105 Deg C)
Switch off.........................195-208 Deg F(91-98 Deg C)



On the ALH at least this thermo-switch is a three pronged on and off device mounted to the drivers side of the radiator that actuates the fan and it's respective speeds. Resistors in this simple on and off scheme wouldn't work. Don't be confused with the resistors others have placed in series or parallel to the coolant temp sensor that feeds the ECM. This doesn't effect the Fan speeds from what I can see in the schematics. We would have to create a simple adjustable circuit that would allow us to set our own temperatures for fan actuation.
 
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josh8loop

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"Lets start heating things up"


I wish I wasn't having 01M transmission problems or else I would be HOT on my hybrid 205 Deg F thermostat testing and evaluation. For now I MUST be very careful with things.
 
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jayb79

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Radiator temps and engine temps are separate components. I think the motor could run at 220 and open the stat and buy the time that coolant reaches the switch it would most likely be cool enough so that the switch would not go on. The radiator is always going to be much cooler then the engine if it is working correctly. This is assuming a moving car.
 

G60ING

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You've now given me the information to feel fairly confident in the use of a 92*C ~ 198*F Thermostat in my AHU. The cool :) part is that they make a fan switch that matches this thermostat for my car.
 

dieselfuel

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I have a feeling, you could dis-able the fan all together, under most circumstances (NOT towing, though).

Again, this is assuming Evans HDTC is being used, as directed.
 

josh8loop

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You've now given me the information to feel fairly confident in the use of a 92*C ~ 198*F Thermostat in my AHU. The cool :) part is that they make a fan switch that matches this thermostat for my car.

Now you have me curious, would the T-stat for the AHU fit for an ALH? 92 Deg C would be better than my stock 87 Deg C I have in there now. Hmmmm.......
 

Tom W.

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You've now given me the information to feel fairly confident in the use of a 92*C ~ 198*F Thermostat in my AHU. The cool :) part is that they make a fan switch that matches this thermostat for my car.
Higher temp fan switch? could you find the part # and post it? Any idea @ what temp it switches on? TX!
 

G60ING

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The fan switch for my tdi isn't the same as your TDI, my TDI isn't your normal tdi. If you click on the link I provided above you will see the options that germanautoparts has available for the mk4.
 

josh8loop

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Radiator temps and engine temps are separate components. I think the motor could run at 220 and open the stat and buy the time that coolant reaches the switch it would most likely be cool enough so that the switch would not go on. The radiator is always going to be much cooler then the engine if it is working correctly. This is assuming a moving car.

jayB79,

Just looked at the radiator, and fan switch this evening. I noticed that the thermo fan switch is more toward the outlet side of the radiator, so it looks like your thinking at least appears to be on the right track. Not sure what the internal radiator passage flow paths are like on these A4 TDI's-that would be nice to know at this juncture.
 

G60ING

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On the corrado, mk2, mk1, b3, b4 radiators the water makes two passes. one side's tank is split into two chambers inlet and outlet. The other end tank is open all the way across.
 

josh8loop

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On the corrado, mk2, mk1, b3, b4 radiators the water makes two passes. one side's tank is split into two chambers inlet and outlet. The other end tank is open all the way across.


Thanks for the info. Next time I'm at the junkyard I will pay attention to a 1.8 Jetta radiator to see it's flow path, maybe it's the same as the 1.9?
 

josh8loop

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Fellas,

Just an update-I had a press tool squared up a bit in a lathe that will hopefully allow me to re-press my 205 deg F "Hybrid" thermostat pictured earlier in the thread. The original one was pressed at a slight angle, and I believe it affected it's performance. I am hoping to be able to retest it soon.

Another hurdle to my progress has been the lack of a fairly accurate way to measure temperture. Instead of purchasing a Scan Gage or similar for $150.00 I needed a fairly low cost alternative. I found one at Harbor Freight for $6.00. It is a digital meat thermometer that has an LCD display hooked to a 1/8" diameter SS probe. It is plus or minus 1.2 Deg F or something like that(close enough for what I need). I saw it on the shelf and wondered if I could remove the sensing element, install it in line with coolant, and extend the wires and remote mount the LCD display without destroying it's accuracy. It turns out it worked great, and is currently installed.

The sensing element is an RTD type, and the added ohm or two from the longer wires has negligeable effect on accuracy. The thermometer can be taken apart, the two sensing wires unsoldered from the board, longer wires attached, and all soldered back together. I even modified one of my dash trim pieces(small one next to hazard switch) to hold the temp display for easy viewing.
 
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dieselfuel

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DF,

In the Bentley service manual in section 19-8, they mention the radiator fan thermo-switch operating temps:

Stage 1
Switch on .......................197-206 deg F(92-97 DegC)
Switch off........................183-195 deg F(84-91 Deg C)

Stage 2
Switch on ........................210-221 Deg F(99-105 Deg C)
Switch off.........................195-208 Deg F(91-98 Deg C)



On the ALH at least this thermo-switch is a three pronged on and off device mounted to the drivers side of the radiator that actuates the fan and it's respective speeds. Resistors in this simple on and off scheme wouldn't work. Don't be confused with the resistors others have placed in series or parallel to the coolant temp sensor that feeds the ECM. This doesn't effect the Fan speeds from what I can see in the schematics. We would have to create a simple adjustable circuit that would allow us to set our own temperatures for fan actuation.
I'm not too clear on what you are saying here, my knowledge of electronics is limited, but what I meant was the resistor would be connected to the fan itself.
 

josh8loop

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I'm not too clear on what you are saying here, my knowledge of electronics is limited, but what I meant was the resistor would be connected to the fan itself.[/QUOTE


Ok so let me see if I got this straight, so you are thinking of putting a resistor in series to the rad fans so that they kick on at standard temperatures but at a slower speed?

I am thinking along the lines of using the current switches as permissives, and adding separate adjustable switches in series with them. So lets just say that the switch for stage 1 changes state from open to closed at 197 deg F, my additional switch that is in series with the first would not let the fan come on
until it's setpoint was reached. Same thing for the stage 2 side of things.
 
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dieselfuel

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Hi Josh,

No, the resistor prevents the fan from turning on until (if) the coolant temp reaches 230F. The key is to find the right resistor.

I have been meaning to call Evans about the Stant t-stat that they use for the TDI and have avalible for purchase. The t-stat they sell is rated @ 215F, according to TomW.

I'll try to call Evans sometime this week and I'll ask about the resistor.

I'll post here my findings.
 

josh8loop

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Hi Josh,

No, the resistor prevents the fan from turning on until (if) the coolant temp reaches 230F. The key is to find the right resistor.

I have been meaning to call Evans about the Stant t-stat that they use for the TDI and have avalible for purchase. The t-stat they sell is rated @ 215F, according to TomW.

I'll try to call Evans sometime this week and I'll ask about the resistor.

I'll post here my findings.[/QUO


DF ,

I cant for the life of me understand where you would place a resistor in our TDI fan control wiring to get that result. That would be incredibly simple! Im thinking that would work for certain types of vehicles with certain fan control schemes, but ours appears to be different. Would
Be very interested in what you find on this topic.
 

dieselfuel

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I don't know. I'm assuming it would be like people using a resistor in the EvryMod: Snipping a wire and installing a resistor. But I don't know.

I'll try to find time to call Evans tomorrow and I'll let you know what I find out.
 

josh8loop

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DF,

Also thinking a little about the construction of thermostats and how they operate we might be able to adjust opening temperatures of thermostats by putting small shims under the large main spring. This would increase the seat load of the main T-stat disc, and increase the force needed to open it by the wax heat motor. Admittedly this type of adjustment would probably be only used to adjust a few degrees here and there, and not the 15 or more needed when using the HD coolant. This is also probably why the failsafe brand of T-stats available from Autozone reportedly increases the coolant temperature-It is physically the same(and looks like it was made by Stant) as the stock Stant t-stat with the addition of spring catch device to hold open the spring when overtemp condition occurs. This spring catch device functionally adds 15-30 thousandths shim to the spring I noticed. Would be interesting for someone to try to add 40-50 thosandths shim to their t-stat to see what happens. I would expect an upward shift in temperature would result. Just a thought :)



P.S.

Don't anyone go overboard with shimming the main spring-It could limit the overall T-stat travel which under certain circumstances(high load) could cause overheat.
 

dieselfuel

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Tom W,

Have you done anything with the heat engine yet?

Josh,

I just got off the phone with David W. @ Evans. He told me they are not currently doing anything with the TDI. They are working on big trucks (Cat, Cummins....).

What Evans is doing is, using a resistor pack on the fan temp sensor to fool the engine computer to think the engine coolant is cooler than normal. Hence, fan not activating til 230F.

David will sell a heat engine, but like I said, at this time they're not doing any testing on the TDI.

Another thought: Does anyone notice their fan turning on under normal conditions without the AC being turned on? I never notice my fan being activated unless I have my AC on. The fan is designed to activate anytime the AC is on.
 

dieselfuel

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Josh,

Would you be able to PM me that scheamtic? My brother in-law is an elctronics engineer. Maybe he could figure something out.
 

josh8loop

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Tom W,

Have you done anything with the heat engine yet?

Josh,

I just got off the phone with David W. @ Evans. He told me they are not currently doing anything with the TDI. They are working on big trucks (Cat, Cummins....).

What Evans is doing is, using a resistor pack on the fan temp sensor to fool the engine computer to think the engine coolant is cooler than normal. Hence, fan not activating til 230F.

David will sell a heat engine, but like I said, at this time they're not doing any testing on the TDI.

Another thought: Does anyone notice their fan turning on under normal conditions without the AC being turned on? I never notice my fan being activated unless I have my AC on. The fan is designed to activate anytime the AC is on.


DF,

I didn't think they would be doing anything on the t-stats for the TDI-too little demand. I think I am on the right(and conservative) track with my "hybrid" method, except the max temp I would get would be around 205 with it. It's a step in the right direction! The resistor pack method on the coolant temp sensor will not work on our TDI's because the ECM doesn't control the fan and it's respective speeds. Our TDI control is rather rudimentery. By the way, I never hear my fans kick on unless the A/C is on-except when I was testing my last iteration of the Hybrid T-stat :D

What would really help me on my hybrid t-stat would be to get a PDF drawing with dimensions of a stock TDI thermostat from Stant. I haven't had time to call them to see if I can get some info. Once I have the dimensions I should be able to use my new press tool I had made up, and repress my hybrid T-stat and test it.
 

josh8loop

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Josh,

Would you be able to PM me that scheamtic? My brother in-law is an elctronics engineer. Maybe he could figure something out.


DF,

Do you have a copy of the Bentley manual? My hardback Bentley is where I got the schematic info. If you have a copy, I can let you know the drawing numbers to look at.
 
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