Colder Thermostat Retro fit (b5/gti to B6)

[Misanthrope01]

Not sure if its just the thermostats that Ive seen for our B6's but there all junk and 100C!?! replaced mine a few times already and getting sick of it.

Im thinking that a traditional style, in block, thermostat(and housing) from a b5 or gti could be used with some modifying to our system (since its used on the b5s). only major changes would be deleting the dreaded J-plug and installing the short loop coolant pipe from a b5 and plumbing it in(in place of the J-plug) and then getting the radiator outlet connected to the thermostat inlet and plugging the now open line on the coolant crossover pipe. (ill be build a new one without it)

this would greatly simplify the coolant system while being able to run a cooler thermostat, 87C even... that is a drastic drop in temp, which really is the main reason Ive been pondering this.

SO, has anyone done this before? or am I crazy thinking I could use a metal thermostat housing, mishimoto 87C thermostat for a gti, b5 short loop coolant thermostat bypass pipe, and b5 lower radiator hose (or cut the bs connection off the b6 and use it)

only downsides I can see would be, thermostat housing might point at the dip stick tube (using the metal gti one) and not having heat as soon in the cabin like I care.

Thoughts? opinions? anyone know why 100c on the b6? anyone got a b5 lower radiator hose theyll part with?

will be ordering the parts to attempt this soon.

[5ktq]

Its possible but you will need to adjust the ECU software.

Basically it has a electric heater in it, so the car runs hotter than a normal 1.8T at low load (increasing efficiency some). When you get on it, it turns on the heater to preemptively open the thermostat so it doesn't overheat.

If the temperature doesn't reach the target, or the electric heater isn't present (which would be the case with a normal thermostat) the ECU will be angry about it.

[A4SoftWalker]

To keep it short the hotter engine temps (as well as smaller intake runners) on the AMB vs AEB were done to obtain a higher emissions rating and to improve engine efficiency on shorter trips; amongst other things.

I wouldn't mess with the thermostat in our cars. It is programmed to interact with other systems in the ecu programming. If you look deeply into it the more you know the more you would respect the thought that went into its design.

Why are you constantly having to change thermostats? Maybe the problem lies elsewhere.

[Matt Devo]

easier just to change the ECU to run at 85C than to try to retrofit in the older thermostat style :)

[Misanthrope01]

easier just to change the ECU to run at 85C than to try to retrofit in the older thermostat style :)

but itsnt it mechanical spring and wouldnt that lead to the ecu thinking the engine is cooler then it actually is? leading to an actual hotter engine? Or would that tell it to start the heater element when it sees 85c coolant and the element would heat the thermostat up enough to open? I dont know, seems kinda backwards to put a heater element into the cooling system to me. I understand the function to open the thermostat sooner, but why not just have a thermostat that opens sooner on its own? (my goal)

A4softwalker: not sure why Im having such bad luck with thermostats. changed one out with the first timing belt preemptively with the first timing belt change at 100k with one from ecs, then it stop functioning last summer, had to get one at O'reilly's and it failed on me not too long ago (warrantied it at least) . boiling water wouldnt open either of them(that failed). Maybe the heater element isnt functioning properly on my car... water pump has been changed on time, and just before the last one failed, always ran distilled water and g13 coolant(pink, prestone)

as far as the thermostat interacting with other systems of the car, what do you mean? I know coolant temp effects what fuel maps are used and what not. but the thermostat doesnt measure that, cant see how simplifying it would effect the 'other systems' you speak of, do explain if you can. Knowledge is what I seek.

[old guy]

This post may help explain how a mapped cooling system works: Clicky click®

[Misanthrope01]

^ that is informative of how it works. But doesnt help with the problem of it not working... maybe my cts sensor at the back of the head is bad? though in boiling water it reads hot and no vag codes thrown... driving around today in 80+ degrees the upper hose on the radiator was hot and the bottom was cool... much cooler... not overheating according to dash (its not accurate, i know) but this cant be good. The fans would kick on after a bit of idling yesterday, So i think the thermostat was operating. but the lower radiator hose being cold disturbs me. A LOT.

and after reading that post, dont see how going to older style unmapped thermostat would effect the computer, yes it will try to open the thermostat early, but if I use a 82C thermostat it will do so on its own. and I could just leave the heater element plugged in so it thinks its working. Ive got a b5 motor sitting around and will probably install the parts off it this weekend and see what happens, yes this is probably blasphemy... but Im rather old school, and would rather have a full mechanical system and trick the computer into thinking everything is OKAY. Will probably try to write out that portion of it when my new rosstech cable gets here. Its a cooling system after all, and theres defiantly more then one way to skin a cat, so why not use the simple way. After all, when it comes to making a great race car (not that Im trying to do that, it's an A4 after all) "Simplify, and add lightness"

If there is a problem that can be pointed out with my thought process please elaborate. I just dont see how removing the computers ability to open the thermostat prematurely, and doing it mechanically, will effect it drastically. Yes I understand Audi's theory behind it, yes it works well on paper, but it is not working for me in the real world currently and is failing me yet again. (Behr thermostat, 3rd one in a year)

[Misanthrope01]

Well, fit the b5 thermostat and the computer didnt care at all in the 40 mile drive I did today. Shows a coolant temp decrease of 20C... not codes thrown with leaving the element plugged in and tied up in the fire wall. (Told the ecu to open thermostat at 82C) duty cycle for the element stays below 4%. so everything seems to be working far better then the mapped thermostat. Warm up cycle works. Fuel trims adjust. nothing seems to be going wrong as of yet and the ecu doesnt seem to care or know it cant open the thermostat as of yet. More testing must be done for sure, but so far its operating without flaw, and there should be more to gain from this... Not sure of how to accurately measure cylinder temps but having coolant 20C cooler should help keep cylinder temps down a bit which is always good for preventing knock and making more power. In the end, my thermostat is functioning and it didnt cost me anything. Ordered a brand new OEM 80C thermostat and housing from ecs just because the one I put in had 120k on it and sat around for 4 years... but confirmed it, it worked before installing. Installation was a breeze, removed J-plug, used b5 style coolant return pipe and everything was plug and play from there (no oil cooler, I run an aftermarket. Return from oil cooler is different on this pipe requiring the B5 oil cooler return hose if your going to use the stock oil cooler)

If anyone is interested I will make a write up on the parts need to retro fit the B5 style colder thermostat into the B6, although it is straight forward using OEM parts. Certainly is cheaper to replace the thermostat with this retro fit, and the engine runs cooler over all. Which certainly is a win. I will continue to monitor it and see if the ecu figures out it is no longer in control of the thermostat, but as of yet, it doesnt care. Yes this might effect emissions, but who gives a shit about that. I dont have the pass that, I dont run a cat, SAI, or Egr at all (AEB head)

[Nollywood]

In the short period I owned my 2003 B6 Avant Quattro SE 1.8T 163, I did exactly the same, using new B5 parts. The original plastic housing was cracked, so I used this opportunity to carry out the conversion.

In a year of motoring, including 2 trips to France, driving through the Autoroute to Paris, the engine never missed a beat, and certainly ran cooler than with the stock electronically-controlled stat.

[5ktq]

Interesting. I like that if it is the case.

What do you need? Different stat and housing. Different top hard pipe. Different lower hard pipe. Right?

[5ktq]

bump for any more information on this.

(Told the ecu to open thermostat at 82C)

can you elaborate on this? did you adjust the flash?

[rocket1420]

bump for any more information on this.



can you elaborate on this? did you adjust the flash?

I'd like to know as well. I'd definitely like to go to a metal thermostat next timing belt change.

[EuroxS4]

Easier to tell the ecu to open the thermostat earlier by changing a few values in the flash file.Just saying.There is a few maps that need to be changed adjusted accordingly.This is just a sample image.

[5ktq]

But then you still have the plastic thermostat, I'd prefer to drop that but then I'm not sure what would be involved software wise.

- change target temperature map(s) to match response of 87C / dumb thermostat
or
- zero error class and/or some diagnostic table for the heater element presence, and temperature out of target range
or
- ???

[walky_talky20]

If you command it to run at the target temp in software alone, you will rely on that little heater element *at all times* to maintain that temp. You will basically be using the crap out of it. As such, the inevitable failure of the element (or the wiring to it) will immediately result in a default temp of 100C+. A pretty lousy "fail-safe".

Using a mechanical thermostat that is actually calibrated to run at the target temperature seems like a better solution, if a cooler, more static operating temperature is the goal. Now, if you wanted to do a short-term experiment with running different temperatures to see which is best, then the mapped system is absolutely perfect for that.

I think the major benefit here is that the temperature stays *constant*, rather than usual roller-coaster of temperatures that the B6 mapped system runs. Temp swings like that are not good for an aluminum head, long-term. That's how you crack stuff.

[EuroxS4]

I dont understand why this is an issue???Thermostat works as its designed.A mechanical thermostat maybe be better but what is the point here??You will not gain anything by switching.Also the 06A audi blocks are machined differently for the map controlled thermostat rather than the mechanical one.Personally I dont think its worth the time and effort.You wount gain anything.

[5ktq]

Less plastic shit to fail, keep the small loop in the block.

I think 06A is machined fine for it, that's how it was set up on passat and MKIV golf with 06A, right? That's why the J-plug is a thing - the hard line comes out from there on non-map variants.

[Matt Devo]

I think 06A is machined fine for it, that's how it was set up on passat and MKIV golf with 06A, right? That's why the J-plug is a thing - the hard line comes out from there on non-map variants.

the thermostat opening is machined differently on the AMB to accommodate the b6 thermostat. If you use another 06A block, you need to modify either the opening or the B6 thermostat itself to fit properly.

[EuroxS4]

Less plastic shit to fail, keep the small loop in the block.

I think 06A is machined fine for it, that's how it was set up on passat and MKIV golf with 06A, right? That's why the J-plug is a thing - the hard line comes out from there on non-map variants.

I don't see your logic here.Less plastic shit to fail??Thermostat is metal on both the map controlled t stat and the mechanical one.On that note both flanges that attach to the 06a block are plastic so in reality there is no advantage if you ask me.As stated you will need to modify the block or the thermostat.


Sent from my iPhone using Tapatalk

[Steve Bassen]

B5.5 water hard pipes and thermostat housing, electric thermostat and j-plug go in the garbage. More reliable, and fixed temperature so the head doesn't run hot as crap (and more prone to cracking) during cruise. You'll need to modify the maps for the thermostat in the ECU like the screenshot of the WinOLS above shows, or the ECU will throw a code for the temperature not being in the target threshold. I had all the parts and info for my big turbo build but sold it all when I went to my noregrats 2.7T swap.

[All_Euro]

Well, fit the b5 thermostat and the computer didnt care at all in the 40 mile drive I did today. Shows a coolant temp decrease of 20C... not codes thrown with leaving the element plugged in and tied up in the fire wall. (Told the ecu to open thermostat at 82C) duty cycle for the element stays below 4%. so everything seems to be working far better then the mapped thermostat. Warm up cycle works. Fuel trims adjust. nothing seems to be going wrong as of yet and the ecu doesnt seem to care or know it cant open the thermostat as of yet. More testing must be done for sure, but so far its operating without flaw, and there should be more to gain from this... Not sure of how to accurately measure cylinder temps but having coolant 20C cooler should help keep cylinder temps down a bit which is always good for preventing knock and making more power. In the end, my thermostat is functioning and it didnt cost me anything. Ordered a brand new OEM 80C thermostat and housing from ecs just because the one I put in had 120k on it and sat around for 4 years... but confirmed it, it worked before installing. Installation was a breeze, removed J-plug, used b5 style coolant return pipe and everything was plug and play from there (no oil cooler, I run an aftermarket. Return from oil cooler is different on this pipe requiring the B5 oil cooler return hose if your going to use the stock oil cooler)

If anyone is interested I will make a write up on the parts need to retro fit the B5 style colder thermostat into the B6, although it is straight forward using OEM parts. Certainly is cheaper to replace the thermostat with this retro fit, and the engine runs cooler over all. Which certainly is a win. I will continue to monitor it and see if the ecu figures out it is no longer in control of the thermostat, but as of yet, it doesnt care. Yes this might effect emissions, but who gives a shit about that. I dont have the pass that, I dont run a cat, SAI, or Egr at all (AEB head)

This with some pictures of the process would be nice