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-   -   Modified Thermostat for higher MPG's... (http://forums.tdiclub.com/showthread.php?t=306799)

josh8loop January 28th, 2011 01:07

Modified Thermostat for higher MPG's...
 
For those that don't want to read through the many pages of this long Thread, here is the Cliff Notes version. Basically I found out that two thermostats can be purchased and parts mixed and matched to give a thermostat that will control at around 205 Deg F for the ALH engine instead of the stock 195. Jump to page 3 post 39 for the part numbers. Page number 4 post 59 shows some photos of the transformation. I have some assembly videos on the construction that can be seen here:

http://www.youtube.com/watch?v=AU8IA...8&feature=plcp


http://www.youtube.com/watch?v=x7hod...eature=related



Remember this is all experimental, and Mod at your own risk. Also, it is not recommended that you fiddle with coolant temps if you have an automatic transmission. With that said, in 15K plus miles I have had no mechanical issues from doing this, and am noticing a 3-4 MPG bump from my previous worn out stock thermostat. I have however replaced most of my old coolant lines, hard coolant pipe seal, and other brittle plastic coolant fittings. At this point we have at least two others that are trying this modified thermostat, and feeding results occasionaly. One of our members also mentioned that a stock MkII thermostat rated for 92 Deg C(197.6 Deg F) will fit the ALH engine too-not quite as high as the "Hybrid" unit, but the mkII version is a drop in replacement. For the longer version on the development of the "Hybrid" version, please read on........ :) ......







Fellas,

I have recently come across information where people have modified their existing thermostats with parts from other thermostats to gain higher coolant temperatures. See here:

http://www.cadvision.com/blanchas/Ra...hermostat.html

Since our thermostats are of the double valve thermostat type it would be important to make sure the end product functioned exactly the same as the old one in terms of internal engine bypass flow control. Not saying that this would be the best idea on the block to help us achieve higher overall engine temperatures, or the most easy to construct, but sense we cannot purchase over the counter T-stats in the ranges desired we are forced to get creative.


Here is a Stant part number of a t-stat that is rated for 205 deg F:

14252(remember your in the non-cliff notes version. Skip to page 4 post 59 for some photos and the part number I ended up actually using to make the "Hybrid")


I hope to do as side-by-side comparison of this thermostat and a replacement for my TDI this evening and see what the potential for swapping the internal parts would be. If the parts look interchangeable, I hope to purchase one of each, and test the 205 degree one to see if it will actually open at 205 degrees. If it opens correctly, I could begin the swap process and testing the results in the car.



One final question I would want to get resolved before proceeding, is it safe for our cars to run at a sustained 205 deg F temperature?

GoFaster January 28th, 2011 06:56

I wouldn't do it - especially on a P-D (which yours isn't).

Higher coolant temperature means higher oil temperature, which means lower absolute viscosity, which means less protection in the critical camshaft/lifter interface. Given that even using 5w30 oil in those engines rather than 5w40 seems correlated to camshaft/lifter failures, this is likely to put it over the edge.

Camshaft/lifter wear-out situations aren't unheard of in the ALH engines, either. It isn't as big of a problem, but still ... thinner oil (lower absolute viscosity) is not heading in the right direction. It doesn't matter if the absolute viscosity is lower due to use of lower nominal viscosity oil, or due to higher temperature; the cam/lifter interface sees it the same way.

jettawreck January 28th, 2011 09:00

Quote:

Originally Posted by GoFaster (Post 3269972)
I wouldn't do it - especially on a P-D (which yours isn't).

Higher coolant temperature means higher oil temperature, which means lower absolute viscosity, which means less protection in the critical camshaft/lifter interface. Given that even using 5w30 oil in those engines rather than 5w40 seems correlated to camshaft/lifter failures, this is likely to put it over the edge.

Camshaft/lifter wear-out situations aren't unheard of in the ALH engines, either. It isn't as big of a problem, but still ... thinner oil (lower absolute viscosity) is not heading in the right direction. It doesn't matter if the absolute viscosity is lower due to use of lower nominal viscosity oil, or due to higher temperature; the cam/lifter interface sees it the same way.

I wouldn't do it either. Higher temps in coolant lead to higher temps in critical areas as pointed out. These engines use oil cooling on the undersides of the pistons for a reason. Internal temps can spike quickly with load no matter that the coolant temp is relatively steady.
Especially would not do if I lived in warmish climate.;)

shizzler January 28th, 2011 09:59

My supposed "195f" stant t-stat allows as much as 209 degrees in normal driving (albeit with reduced airflow to my radiator - grill blocks).

I know cam wear is a real issue on the PDs... but I would suspect most issues of premature wear on an ALH are due to using the wrong oil in the first place (or a very punishing driving style - excessive time at high rpms, etc).

Quality synthetic oil does not break down until well over 300 degrees F. How many of you have an oil temp gauge? Before I got my hotter t-stat and blocked my grill off, my oil would run around 180f at 70mph cruising - a.k.a COLD! On hot summer days I have pushed it as far as 250f on hill climbs. This is still NOTHING to worry about. We test modern diesel engines at work for 500 hours straight at full rated power conditions and oil temperatures of 270f or MORE. No problems.

The theory and concern you guys are talking about is sound, but perhaps a little too cautious. Higher oil temperatures is a good thing. The decrease in viscosity should not be enough to warrant excessive wear.

However to the OP - why would you want more than 205 f coolant? In my opinion this is about as reasonably hot as you'd want it to be. I don't think you'll find much more increase in efficiency from running much over 200f - it's the people stuck down below 170 with faulty thermostats that pay a penalty in economy. And if you take your engine, fully heat-soaked on a humid summer day, and try to blast up a mountain, you're going to be sorry if you cross mush more than 230f, which is entirely possible.

Proceed with caution - and monitor those gauges (not the dash gauge!) closely.

UFO January 28th, 2011 17:33

Higher engine temperatures can also close internal engine clearances. You may end up hurting fuel economy by running higher than normal.

GoFaster January 29th, 2011 09:48

Quote:

Originally Posted by shizzler (Post 3270218)
The theory and concern you guys are talking about is sound, but perhaps a little too cautious. Higher oil temperatures is a good thing. The decrease in viscosity should not be enough to warrant excessive wear.

In a P-D, the use of 5w30 instead of 5w40 appears to put them over the edge. Increasing the temperature only a few degrees can have the same reduction of absolute viscosity that the use of 5w30 instead of 5w40 does.

The ALH engines aren't as sensitive, but camshaft/lifter wear is not completely unheard of on those, either.

josh8loop January 31st, 2011 09:05

Fellas,


Thanks for the warning in regards to oil viscosity etc. That seems very important especially with the PD motor. I also find it interesting that many guys with the 7.3 L diesels are running higher temp thermostats(203 Deg F). Sounds like they are getting a little better FE, and performance. I realize that this is not the same motor and all and many things are different between them but I still feel comfortable running at a nominal 205 Degrees.

This weekend I went ahead and purchased two thermostats. A Stant 195 replacement for my car, and a 205 Degree Stant thermostat that I mentioned earlier in the thread. I noticed that quite a few parts were interchangeable between them, most notably being the "Heat Motor". I went ahead and characterized the T-stats in water, and noted their min and max travel limits. This will be helpful to have when evaluating the completed hybrid T-stat. I have disassembled the 205 degree unit, and am in the process of carefully disassembling the 195 degree unit now. Once the hybrid unit is complete, I will test it extensively to make sure it has a high opening temperature repeatability. In the end, this may not be the exact method I will use to control the ultimate temperature of my engine, but I am learning lots in the process.

AndyBees February 1st, 2011 19:53

I bet the increased fuel economy you are trying to achieve will be disappointing to you......... and, you will destroy the engine in the process! Sort of like High Blood pressure.......... gotcha! Bam!

david_594 February 2nd, 2011 12:14

I went with a 93 degree Celsius thermostat for a few years, going from my 87 degree stock one and notice no significant improvements in fuel economy(which was the goal).

During hot summer days though the cooling fans would come on for an after-run cycle after shutting the car down which ended up being the major factor in me swapping back to an 89 degree thermostat.

If you do decide to do it, let us know how it works out. I get the impression you understand the risks and that running the motor hot could have negative consequences.

ihatespeed February 2nd, 2011 14:15

Just a little food for thought.. Back in 2006 nissan had major engine failures in their 2.5l altimas, turns out the engines were running a little hot, Nissan intended it.. they did not foresee the oil consumption issues and the resulting engine failures. the fix was to lower engine oil temp by a little bit. There were many 10000-12000 mile engines replaced that year. water temp and oil temp are two very different things. and just because synthetic oil does not catastrophically fail under 300 degrees does not mean its still performing properly and within grade.

Quanger February 2nd, 2011 15:52

Too risky in my opinion as well. If you think the cold is hurting your fuel consumption, just stick with blocking the front end with those foam pads. MPG drops in winter because of the cold starts as well as winter fuel.

KB3MMX February 6th, 2011 15:09

Quote:

Originally Posted by josh8loop (Post 3269785)
Fellas,

I have recently come across information where people have modified their existing thermostats with parts from other thermostats to gain higher coolant temperatures. See here:

http://www.cadvision.com/blanchas/Ra...hermostat.html

Since our thermostats are of the double valve thermostat type it would be important to make sure the end product functioned exactly the same as the old one in terms of internal engine bypass flow control. Not saying that this would be the best idea on the block to help us achieve higher overall engine temperatures, or the most easy to construct, but sense we cannot purchase over the counter T-stats in the ranges desired we are forced to get creative.


Here is a Stant part number of a t-stat that is rated for 205 deg F:

14252


I hope to do as side-by-side comparison of this thermostat and a replacement for my TDI this evening and see what the potential for swapping the internal parts would be. If the parts look interchangeable, I hope to purchase one of each, and test the 205 degree one to see if it will actually open at 205 degrees. If it opens correctly, I could begin the swap process and testing the results in the car.



One final question I would want to get resolved before proceeding, is it safe for our cars to run at a sustained 205 deg F temperature?


205F has never and will never hurt any diesel engine as long as the coolant pressure and mix ratio are correct to prevent boil.
Basically the temp difference you are trying to achieve is like the Powerstroke guys doing the 203F thermostat.
If oil is really a concern, run a 5w-40 synthetic but it won't get anywhere near hot enough to damage anything at a measly 205F , geesh. If you were talking about a 215-220F thermostat, I might be a little more cautious but even that isn't enough to damage a properly mixed and pressurized cooling system.
Gas engines are a different subject and have different things to battle with higher heat like detonation or preignition, vapor lock,etc...

josh8loop February 7th, 2011 09:13

Fellas,

Thanks for the input on this topic, greatly appreciated! I will admit, this project is a little over the top, but I feel pretty confident that if I am careful I can pull it off. Now whether or not I see MPG increases, and if the risk of making my own thermostat that could possibly fail while in service is worth it is another story alltogether.

josh8loop February 7th, 2011 09:26

KB3MMX,

Thanks for the encouragement. I had seen the 7.3 liter diesels, and their 203 deg F thermostat upgrades, and noted that they mentioned increased performance, and MPG. That, and the fact that it seems hard to get a thermostat that accurately functions at the rated temperature is what basically started this whole thing. My wife recently took a hard fall breaking the ball that connects her arm to her shoulder so that has made my project take a back seat at the moment. This is also allowing me ample time to consider the risks and rewards of such a project.

I am glad you also mentioned the properly mixed coolant, and proper pressurization to prevent boiling. I have recently replaced my coolant reservoir, and coolant cap along with some other cooling related parts and seals, so I know they are up to the elevated temperature/pressure. A scan guage needs to be in my future if I move forward to the trial part of this evolution.

Ski in NC February 7th, 2011 09:31

Another thing to consider: These engines use an Al head on a Fe block- There are different thermal expansion coefficients. As engine heats and cools, head tries to expand more than block. Stress appears in both. There may be some relative motion (scrubbing) on head gasket, depending on coefficient of friction and clamping force.

So putting a hotter tstat will cause more range in the thermal cycle from cold engine to hot engine. Head gasket may not be happy with that.

Not sure if this is an issue with these engines (head gaskets seem pretty reliable) but other engines with this Al/Fe combo have had problems (e.g., some toyotas).


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