Project Thermostat

whodwho

Original poster
Member
Mar 7, 2019
41
CA
My Envoy was getting bad mileage, I drive mostly short city trips so that doesn't help. I was getting less then 200 miles a tank, I know it wont get a lot better for my driving but looked into it.

From research I had the stuck thermostat issue going on, It would take forever to warm up and not get to optimal temp. It would mostly be between 155-170 and never seen it over 190. Reading up more it seems to be a very common and problematic issue and read that some have issues again within a couple years or less of replacing one. I don't mind making repairs once but don't fancy repeating it unnecessarily... 8^(

Which brings up to project thermostat. Since it was stuck open(or too quick to open) I thought to try an inline thermostat, easy to get to and easy to find a replacement if ever on the road and needed to replace it. It takes 10-15 mins to change with just a screw driver and an allen wrench and easy to catch and recover the coolant. It uses a very common generic old school Chevy thermostat that cost ~$5 and will be inexpensive to try different temps to find an optimal temp for efficiency. If it works out well I will pull the old original and gut it or replace with a new one if not.

I was able to use the original top hose and cut the need angled sections to fit it nicely between the engine and radiator. It is mounted at a slight upward angle so any air will make it to the top radiator tank. I drilled a small 3mm hole for bleeding any air and to allow a small bit of circulation to allow the thermostat to work correctly being away from the engine.

So far it is working well and temps are within the range expected, It came with a 180 and ran that for PoC until I got a couple new ones. I am currently running a 195 and have a 205 to try at some point to see what effect it will have on efficiency. With the 195 and a cold start it will get about 204-206 and open, after the first cycle and when warm it will maintain 198 at idle, 197 light cruise and about 200 under a load. I need to find a local hill to get a bit more load on it to see how it does.

I recently got a ScanGauge and the before and after shows that it seems to have helped the mileage, I need to get a couple tanks thru it to get it calibrated to get accurate mileage readings from it.

Looks right at home 8^)

uc
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Interesting method you chose there. The stock thermostat is definitely in an inconvenient spot for R/R, that's for damn sure. Hope this works out long term.
 

droptopgsx

Member
Nov 11, 2013
8
In a normal thermostat the wax pellet is submerged in flowing coolant so that it can properly regulate the coolant temp in the engine block. What you have there is a crappy valve in-line that is going to do a horrible job of controlling the temp of the engine since it is nowhere near the engine, the coolant has to be flowing through via some kind of a jiggle/bypass valve (since if it was 100% closed warm coolant wouldn't get to it the way it is setup and it wouldn't be working at all), and is flowing warm coolant inside the radiator before the engine has even fully warmed up making warmup take longer and overheating much more likely since the rad is going to reach operating temp at the same time as the rest of the engine.

I'm sure it works better than leaving a faulty open t-stat as-is but it is in no way anywhere near as good as simply replacing the oem t-stat and fixing it correctly. The factory stat is fine, lasting 60-100k miles and taking at best an hour to replace.

Your car to do with what you choose but understanding the purpose of thermostats and how they are designed to work and how the engine management system expects them to work I urge others not to do this.

My $.02

Edit: additionally, leaving the known-faulty oem stat in is not only adding more restriction to flow in the cooling system but more importantly it is just ASKING to have it fall closed and cause rapid overheating and still requiring replacement. Doing what you have done isn't increasing reliability at all but actually adding ANOTHER failure point in the system.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
:iagree: And it's also in the wrong place. Coolant circulates from the thermostat through the lower hose, through the radiator where it is cooled, then through the upper hose into the engine. You are regulating the cold coolant. For this to work properly, it should have been installed in the lower hose.

I know it's a bitch of a job but it better to do it right. This janky valve setup is just inviting disaster when the weather gets hot and A/C is running.
 

whodwho

Original poster
Member
Mar 7, 2019
41
CA
@droptopgsx If you are going to take the time to post I would of preferred a discussion vs an attack on the project 8^(

flowing warm coolant inside the radiator before the engine has even fully warmed up making warmup take longer and overheating much more likely since the rad is going to reach operating temp at the same time as the rest of the engine.

Many thermostats come with a bypass hole (with and without jiggle valves).

There is zero reason to do this except for laziness, the factory stat is fine, lasting 60-100k miles and taking at best an hour to replace.

As mentioned the lack of dependability/longevity is the main reason for this experiment and the relocation, in reading on the subject many even Mooseman mentions their issues with thermostats.

From reading others experiences I sure would like to see a video of you doing a thermostat change in under an hour!

Edit: additionally, leaving the known-faulty oem stat in is not only adding more restriction to flow in the cooling system but more importantly it is just ASKING to have it fall closed and cause rapid overheating and still requiring replacement. Doing what you have done isn't increasing reliability at all but actually adding ANOTHER failure point in the system.

Since you took the time to go back and edit your post but not looking like you read all/any of my text I will leave this here:

"If it works out well I will pull the old original and gut it or replace with a new one if not"
 
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whodwho

Original poster
Member
Mar 7, 2019
41
CA
:iagree: And it's also in the wrong place. Coolant circulates from the thermostat through the lower hose, through the radiator where it is cooled, then through the upper hose into the engine. You are regulating the cold coolant. For this to work properly, it should have been installed in the lower hose.

I know it's a bitch of a job but it better to do it right. This janky valve setup is just inviting disaster when the weather gets hot and A/C is running.
I had read that and looked into it, not sure where it originated but it flows the conventional way. The thermostat location is not and I still need to do some research on the theory of that to further evaluate the project.

I live in SoCal so it is warm and the AC is always on 8^)

I have monitored the temps and it is working well, it holds within a couple degrees of hysteresis. I will have to break out the GoPro and video the ScanGauge of warm up and driving.

Sorry for posting a project with a "crappy valve in-line" / "janky valve setup", I thought this forum was going to be more open minded and actually discuss and not just criticize 8^(
 

Mektek

Member
May 2, 2017
656
FL
I like both the effort and the response. I curse GM for making what should be a simple task - difficult.
The hose at the top is already short, and by adding a rigid section it will flex the plastic radiator much more.

II think this is a good idea. But first remove the thermostat from the original housing at the engine. Then install the inline unit in the lower hose.
 

whodwho

Original poster
Member
Mar 7, 2019
41
CA
I like both the effort and the response. I curse GM for making what should be a simple task - difficult.
The hose at the top is already short, and by adding a rigid section it will flex the plastic radiator much more.

II think this is a good idea. But first remove the thermostat from the original housing at the engine. Then install the inline unit in the lower hose.
Thank you for constructive criticism. The designers don't always think about repair and has been an age old complaint for techs.

The engine is mounted pretty stout and does not appear to move much. If it works out to be a worthy project the outlet pipe can be cut down and a bead crimped in to give a little more flex room in the hoses.

As noted I fully intend to either gut or replace the old thermostat with a new one, I didn't want to do the work twice if it proved not to have a favorable outcome.

Installing in the lower hose would not work as the pellet needs to be in the hot side stream and with the stock non traditional thermostat location it receives the cold stream which seems odd and maybe why the thermostat gets over cycled and fails.

Thanks again for your feedback
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Please don't take opinions of your work as personal attacks. You posted a method of possibly making a job easier for now and in the future. Some came out and said it was interesting and others brought up valid points as to why it may not be a good idea and possible ways to correct it. People here have lots of experience on this platform. We don't know your experience level being a new member.

Lord knows we're all into creating shortcuts and ways to make things easier. However, for some things, they are best left mostly stock, such as the cooling system, where a failure could be disastrous. If there weren't any other options for thermostats then yeah, this could be a good option. However, parts are plentiful. We are even anal here about using ACDelco parts most of the time because these trucks are really picky. This we learned from experience.

I've done so many of these thermostats I could probably do it in an hour. Doesn't bother me in the least. In my early days on this platform, I drank the e-fan koolaid and found out what others knew that they don't work as well as a mechanically driven fan on these trucks. Why screw around with a proven system? If your mod is proven to work long term, then that can be a possible mod people could do at their discretion.

'Nuff said.
 

whodwho

Original poster
Member
Mar 7, 2019
41
CA
Thank you for the reply, my replies here are not directed at you or anyone directly

Please don't take opinions of your work as personal attacks.

I thrive on discussion and I don't mind constructive opinions/criticism, that can only make a project better but being told something is wrong without merit is not welcome.

You posted a method of possibly making a job easier for now and in the future

The objective of the project is not "making the job easier" or "creating a shorcut" it is to alleviate what appears to ME as a weakness and as a side advantage yes it is easier to replace. I would not look forward to replacing it on the side of the road in the stock location...

I don't mind doing the work(my susp rebuild thread as example), although I am not currently in the industry I have a lot of tools from being in the trade and I still have a heavily customized project car and I love using them for whatever and whenever I can 8^)

'Nuff said.
100% agree, enough of that chit and hopefully I am past my newbie initiation now 8^)

Now for a call out on you and the coolant flow as promised, I did some quick searches this morning and not the easiest to find much on the relocation of the thermostat but found a thread that has more then you would ever want to know about cooling systems.

I am still reading it but found a couple relate tidbits of info

The thread:

A pic for reference:
LS%20cooling%20system%20-%20overflow%20tank_resize.jpg


TidBit said:
The Gen III/IV inlet thermostat location is designed to eliminate the following conditions / problems:

With the older outlet design, an air pocket could be created under the thermostat after the thermostat was installed following maintenance or service to the cooling system. Since the coolant was prevented from reaching the thermostat's wax motor, the thermostat didn't open and allow cooling to begin until the air pocket had gotten hot enough to cause it - which would happen much later than for coolant, and often too late to prevent overheating and component damage. This excessive heat would be bad for any engine, but can be especially damaging for aluminum components. Elimination of this air pocket is one of the reasons why old-school racers would drill a small bleed hole in the thermostat's flange.

The second problem is thermal shock that may occur at the radiator when hot coolant is released by the thermostat when the ambient temperature is near freezing. This sudden release of very hot coolant to a very cold radiator could cause thermal stress cracking in the radiator.

Because the old-style thermostats were located at the top of the engine where coolant temperatures are highest, and because any vapour or trapped air always seeks the highest point in a system and therefore could get trapped beneath the thermostat, this design can lead to unwanted thermal cycling as the area of the thermostat heats and cools causing the thermostat to repeatedly open and close. The newer inlet location design was designed to eliminate this potential thermal cycling problem.

So non of which I am overly concerned with at this point of the project, I still find it odd for the relocation as that would seem to promote the radiator to run at engine temps and/or over cycling the thermostat??

A simple confirmation that it applies to us is grab both upper and lower hoses when up to temp and see which one is hotter.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
A simple confirmation that it applies to us is grab both upper and lower hoses when up to temp and see which one is hotter.

Somebody pass me the crow :redface:

I REALLY had to dig for this one and found it in one of my hoarded docs which have become difficult to find on the Net.

Starting on page 29:

The water pump is a cartridge style unit with the inlet and outlet formed into the block and front cover assemblies. The flow is directed rearward through the block and forward through the head in a “U” pattern for optimum cylinder cooling.

The thermostat has an opening set point of 88C (190F) and is positioned on the inlet side of the cooling circuit to maintain steady control temperatures.
 

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whodwho

Original poster
Member
Mar 7, 2019
41
CA
Somebody pass me the crow :redface:

Here ya go! 8^)
download.jpeg

It looks to be a common assumption from the location of the thermostat and being used to old school way that that a thermostat controlled the flow from the outlet of the engine to the inlet of the radiator. I found a few posts with this discussions/arguments going on

oh and nice document, thank you
 
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Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
I thought I remembered, when helping a friend change the t-stat on his XUV and we were burping the system, that we could see coolant flowing into the radiator from the top hose. It was several years ago, so I wasn't sure, but glad to know I wasn't misremembering (this time :tongue: )
 
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whodwho

Original poster
Member
Mar 7, 2019
41
CA
So a quick follow up on this, I did a weekend trip to a buddy of mine in Bullhead City AZ. It was ~106 there and the temps behaved as expected. Pulling the steepest grade with the air on and cruise control @70+ it was ~216 and ~203 on cruise.

My mileage was 21 mpg avg so I was ok with that. It was 300 miles and had 1/4 tank left, city driving I have been barely getting 200 miles at best on a tank.

With a safe and successful return from that trip I am going to see what the 205 thermostat does for temps and any influence on the mileage in city driving where it rarely sees over 198.
 

Mektek

Member
May 2, 2017
656
FL
I just looked up the price of the inline thermostat housing on fleabay and it was surprisingly expensive.
I'd like to find a replacement for the thermostat only so as not to replace a perfectly good housing.
And an electronically controlled thermostat would be interesting too.
 

whodwho

Original poster
Member
Mar 7, 2019
41
CA
I had found a used one on there so that helped, and the thermostats are < $5 and the stock one seems to need to be replace a few times so I figured it would pay for itself 8^)

I had thought about electronic controlled and look into is some. I thought it would be a PWM controlled valve, I was surprised to see it is just a controlled heater for an old school wax pellet thermostat.

And hopefully with one of the goals of the project, savings from better mileage in the city where I do 90% of my driving.
 
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whodwho

Original poster
Member
Mar 7, 2019
41
CA
Another quick update to this project, I delayed installing the 205 as I had another long trip planned and wanted to make sure I had no unwelcome surprises. I did a 1k round trip to San Francisco and all went well.

I put the 205 in a couple weeks ago and is working well and holds @ a better temp around town. It opens on warm up about 210-211 and then holds about 206-207 driving around town. I think I will leave it with the 205 in and see about the mileage settles in long term.
 
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