I want to replace my stock thermostat with a 180 degree one but on the FAQ on the main page of this site says you have to reprogram your prom if you want to change your thermostat. If I drop my thermostat to a 180 will I have to reprogram my prom?

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1989 Iroc-Z 5.7 350, Blue, T-Tops
Lightly Moded:
Headers, Rebuilt B&M 700R-4 tranny, Airfoil, K&N's
-- Blue LED backlight Dash
"Just some 17 Year old spending every dollar I make on my car."

 

No, you dont need to but just so you know the fan will still turn on at the same temp its set at (around 230ish) so it will still run hot in traffic, but not on the freeway.

 

That is not true. There are settings, even at 180* that will not work unless the CTS temp that enable them is altered.

IAC Block Learn, Desired Idle Speed vs Coolant Temp, %Fuel Add vs Coolant Temp, Spark Add vs Coolant Temp are just a few that will be "off" with a 180* T-stat. 160* effects even more; possibly affecting Block Learn entirely.

The changes needed vary from ecm to ecm. But you have to make sure all the "little" things inside the eprom are changed or the eprom will not function optimally or correctly. It is part of the reasons why a cooler t-stat will often burn more gas than a 195* T-stat.

Often people will swear on a stack of bibles that their car "feels faster" with a colder T-stat. A lot has to do that they are getting extra fuel and possibly extra spark. This will make the initial "stomping on it", produce more power but as they progress through the powerband they in fact may be going slower because they are often running overly rich.

By adjusting the pump shot and playing with spark advance within the eprom, they can accomplish that same "initial" feeling they get with a colder t-stat but now they can get the mixture proper throughout the entire powerband. In fact, when properly setup, a 160*, 180* and 195* can be setup to damn near perform all the same.

I did find that even then, the 160* would tend to burn a little more gas and was a little trickier in getting consistent performance as the engine was not at it's optimal operating temperature. Thus I personally have swapped back to a higher temp T-stat (180*) as I can get the same performance from it as I could with the 160*, and more consistently while not burning quite as much gas.

[This message has been edited by Glenn91L98GTA (edited September 24, 2001).]

 

Like what specifically?

I remember when computer controlled cars first came out, the rumor was you couldnt modify anything without modifying the chip... I find it humorous that it seems the trend is heading that way again. From my experiences with TPI cars since they came out I have found that all these little things that supposedly will blow up your motor or cause major problems never surfaced. If you really believe that changing to a 180 stat makes that much of a difference, you had better never modify a single part on the car from front to back without reprogramming it. And dont ever drive it in cold climates with the heater on because even in the relatively warm areas of Cali I have seen the temp lower than 180 on a stock thermostat. I can just imagine what catastrophies happen if someone owns a thirdgen in Alaska.

[This message has been edited by madmax (edited September 24, 2001).]

 

Not that I've delved into the PROM much, but I run a 170 stat, with as on 200/off 185 Fanswitch.

My L98 with 110K averaged 25.5mpg (2.77's, 700R4) with the stock PROM, 70-75mph with the A/C on, during all highway driving. factor in the "claimed loss of MPG's" in the 3-10% range since Ca. went to MTBE fuel mix, it seems the ECM is okay with the setup.

I haven't checked the MPG's since I did my headwork, intake and exhaust, so I may be getting one of the pocket programmers soon

 

Again, it all depends on the ECM. SD has even more funny little things that need to be adjusted, including the MAT Inverse Lookup Table, especially if you are using a relocated MAT.

All those "little" things are reasons why a person's idle may be a little higher, a "stumble or hesitation", or erratic idle...all affecting the overal driveability of the engine.

Some of these issues may be hidden if the person has added a lumpy cam, but they may also be "living" with some driveability problem - assuming its the cam, when in fact, it may be a simple setting in one of the tables/constants based on a lower CTS reading that is the real cuprit.

It is best to do a thorough search in the appropriate hac on the CTS to see all the things affected or rely on the CTS. And even then, the ECM may be using a "temporary" RAM variable instead of the actual CTS variable in RAM.

When I changed my T-stat on my SD car, I even found that the values I used in my VE tables had to be changed to get back to 128/128. This is how I found the effects of the CTS on my SD car. It would not surprise me that the MAF cars may need some tweaking to the MAF Scalar tables if you were originally 128/128 perfect and then switched to a different T-stat.

[This message has been edited by Glenn91L98GTA (edited September 24, 2001).]

 

Actually, you should reprogram the stock chip on a stock engine. I have found in virtually every engine that I have looked at, that the stock eprom tends to be overly rich right from the factory.

Then you add in those "time honored" mods (increase fuel pressure, install lower T-stat, relocate the MAT, bypass the TB, etc) which ALL tend to richen the fixture FURTHER, and you have a recipe for a dog. The WORST thing to do on a basically stock engine is to richen the mixture...you need to lean it.

But, tweaking the eprom for all of those things will correct most of the problems. The "tweaking" that has taken up the VAST majority of my 200+ eprom re-burns has been spark advance and controlling the knock sensor. Did you know the knock sensor has a tendency to go "deaf" when a lot of knock is detected and then you get REAL ping...at which point the knock sensor ceases to function - until you back off the throttle.

What is worst, if your car is set up where it can have a fair amount of advance (like adjusting the distributor up 4*); should the knock sensor get saturated, then your TOTAL TIMING will go to what the MAX values are, further making the problem worst.

The bottom line is we have a much better understanding of what the eprom does (and does not do). A lot of those tricks are just that, tricks, to fool the ECM since most guys didn't know how to get inside the eprom or what was really in there.

Don't be surprised if MORE "time honored" mods are proven wrong. So far, one of the WORST mods is the relocated MAT...on SD, you must adjust the MAT Inverse LookUp Table or you'll run overly rich at some temps and lean at others. With MAF, it basically does nothing other than disable your EGR sooner than intended.

 

Have you ever read thru the Source code to an ecm?.
There is a difference from runs, or runs OK, to runs correctly.
Bruce

 

What does the "MAT Inverse Lookup Table vs Delta MAT" table mean anyway? That description might as well be in Greek.

I've got a 160 degree thermostat and a relocated MAT. All the temperature tables I see in my $8D TunerCat TDF file show temperatures well below 150 degrees, so I dont see how a 160 degree thermostat would hurt.


------------------
1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Just as Grumpy said "Have you ever read the hac and spent any time reading it"? You'd be surprised what little goodies are inside. Do a search on the CTS and note how many tables are dependent on it.

 

I'll speak from experience here. I just finished putting in a brand new 195 degree t-stat. I had put a 180 degree one in three about a month and a half ago. The car had more pep for a longer period of time (it took longer to heat up). I got even worse gas mileage with the 180. The reason why you some get a cold t-stat, no chip burning, and still get great mileage is because they "run the a/c while doing 75-80". Running the A/c makes your temp go up faster. So does running the higher rpm of 75 - 80 mph. Your car doesn't go into closed loop until it hits that certain degree (I can't remember where...but not near 180 or 160). If you run the ac and go fast, you are effectivly bypassing the bad effects (and some good) of having a colder t-stat. You go into closed loop like normal. For those like me who don't ever use the a/c (yes even in that 105 * Texas heat) and try hard to avoid the tickets, the colder t-stats do more damage than good.

Just my .02

 

Grumpy, yes I have. What I see for block learn is 50C which is 120F. SD may be different but I never bothered to look since I dont own one and neither does the poster.

Glenn, as for improvements on the factory setup, thats kind of a moot point. If you change only the thermostat and nothing else, the car just ends up running 12 degrees F cooler all the time. On the cars with the cold start injector, its not on. Do you think the factory didnt anticipate the car running a few degrees colder than the stock thermostat temp? I really doubt it. Cold climates or cold weather will easily send the temp below the thermostat rating, especially with the heater on. The way you are phrasing this is like the car runs super rich at 180 degrees, but not 192. Doesnt make much sense to me. It doesnt appear that way from sniffer experiments I have done either. And just FYI I had to check to make sure everything was working properly on a swap I did (aside from the EGR since there was none) and it was all fine with a 180 stat, never saw anything not working like it should have in the week or so of staring at a scanner.

Like I said above, if you want perfect, dont touch a single thing on the car including the air filter.

 

Max, believe as you wish, but either you have not read any hacs at any epth or understand how the Assembly Language works. Have you found the IAC Learn Mode Enable/Disaable Temp? Read the hac and trace the all the places where the CTS is referenced, including the calculation of the injector pulse width. When you do, then you will see the error of your statement.

And yes, GM did anticipate the T-stat to run in these cars. That is why I have to fight with the Parts Department when I explain to them when I want a non-stock T-stat (195* BTW).

As for "not touching anything and leaving it stock", the stock eprom itself leaves a lot to be desired - so that is not an option either.

 

AUM/BUA Closed-Loop Operation Parameters
CTS < 14.7°C (58°F) for 75 seconds;
CTS >14.7° (58°F) and < 40.7° (105°F) for 51.4 seconds;
CTS >40.7°C (105°F) for 12.5 seconds;
O2 >0.699V & O2<1.99V for 10 seconds;

Coolant Temperature Sensor Related Parameters
BLM enabled between 50°C (122°F) and 140°C (284°F)
Cold spark advance disabled above 56°C (133°F)
Hot spark retard begins above 116°C (240°F)
Highway Mode spark advance > 59.8°C (140°F)
Knock sensor disabled below 66.5°C (152°F)
Power enrichment at base A/F ratios > 56°C (133°F)
Target IAC idle RPM >80°C (176°F)
IAC multiplier at 1.0 (base) > 32°C (90°F)
Knock Control enabled > 67°C (153°F)
EGR Duty-cycle enabled at 56°C (133°F)
EGR Duty-cycle at MAX >80°C (176°F)
TCC lockup enabled >50°C (122°F)
SHIFT light enabled >50°C (122°F)
Diagnostic communication enabled at 70°C (157°F)
DTC 43 enabled > 90°C (194°F)
Cooling fan #1 enabled at 107°C (226°F)
Cooling fan #1 off at 104.7°C (220.5°F)
Cooling fan #2 enabled at 115.2°C (239.5°F)
Cooling fan #2 off at 110°C (230°F)
Cooling fan duty cycle at 100% at 80°C (176°F)
Acceleration enrichment multiplier at 1.00 below 80° C (176°F)
Acceleration enrichment multiplier at 0.75 above 80° C (176°F)
Acceleration enrichment multiplier at 0.50 above 104°C (220°F)
Acceleration enrichment decay factor at 25% below 80° C (176°F)
Acceleration enrichment decay factor at 40% above 80° C (176°F)
Acceleration enrichment decay factor at 50% above 104° C (220°F)
Acceleration enrichment decay factor at 60% above 128° C (262°F)
Fuel limiting factor timer at 217 counts below 80° C (176°F)
Fuel limiting factor timer at 169 counts above 80° C (176°F)
Code 13 (oxygen sensor fault) enabled above 70°C (157°F)
Code 14 (CTS high fault) enabled above 130°C (266°F)
Code 32 (EGR fault) enabled above 30.5°C (87°F)
EVAP canister purge enabled above 70.3°C (158.5°F)
Hot closed-loop timer enabled above 70.3°C (158.5°F)
Rich/Lean O2 offest at 16 counts between 20°C (68°F) and 92°C (197.5°F)
A/C clutch disabled above 150°C (302°F)

Miscellaneous
25.3° maximum allowable knock retard when not in WOT

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Later,
Vader
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Justice and Freedom will Prevail

 

I guess I should have mentioned a bit more.

My temp gauge doesn't even climb with the A/C on, at the most, it's increased a few degrees, so little that I can't tell the difference between the temp with the A/C on or off.

If you engine runs noticbably hotter with the A/C on, then your cooling sysytem is inadequate.

And yes, where I live and drive, triple digit temps are common, mid to high 90's the norm.

Since our gauges are so in accurate, I can't place an exact number on the temp, other than it NEVER runs as warm as it did when I ran 195 Tstat's in it, via watching where the needle mark is.

 

Vader (or other PROMmies),

Could you explain what the parameters you've listed mean, and how they affect drivablity/performance?

 

It is 192. Check with the powertrain engineer at GM.

 

Assuming an ideal thermostat and operating range of 180 (AHAHAHAAHHAAHAHAHA UMmmmmm yea sure... ideal... LOL) the only thing I see in Vaders stuff is code 43 check... I sure hope its not pinging at that temp.

I look at it this way... the car, at some points in time due to natural conditions, will run at 180 degrees. The programming cant be much more off than it is already right out of the factory door due to more than just driveability and emissions. And fortunately the CTS is at the hottest spot in the motor, so its not gonna be any colder than it has to be.

The only requirement I see is closed loop, other than that it looks like an open field to me. If you are sure its there in the MAF code, point it out to me because I only see things referencing to the lookup table and modifying the number based upon the coolant temp which Vader listed the parameters for above.

Boy didnt this leave the 180 stat question...

[This message has been edited by madmax (edited September 25, 2001).]

 

Jeff, thanks for the rather comprehensive list. But the original poster has a $6E (1989 MAF), which has EVEN MORE things affected.

Since no one mentioned the IAC Learn temps; look at address x'C598 for the IAC Learn Minimum Temp (85*C) and x'C5999 for the IAC Learn Max Temp (121*C) for the $6E. A 180*F t-stat causes your IAC Learn to cease to function, plus even more things than Jeff mentioned as the CTS controls more on a $6E. As I said every ECM is different, along with the $32 and $6E used on the 165.

As for T-stats, typically a 160* T-stat operates at 68*C, 180* at 79*C and 195* at 92*C; ALL plus/minus a couple degrees due to tolerance and driving conditions. Based on my running EACH of those T-stats at one time or another, pluse similar data that I have gathered from other friends cars. But those are the typical operating temperatures measured at the CTS for the 3 commonly used T-stats.

If your T-stat is functioning properly, the COOLDEST it will drop is a couple degrees under the following conditinos: Cold weather, no load. You accomplish this going down a hill (without gearing down) on a cold day. But it only drops a couple of degrees (if it is functioning properly). A 195 (actually 92*C typical operation) will NEVER drop to 80*C (typical 180) EVEN when going down a hill on a cold day. I have driven in -10*F weather (and hills) and it STILL functions the same.

The only time a 92*C T-stat will be at 80*C, is when starting up, IF it is functioning properly. If a 92*C t-stat drops to 80*C then the t-stat is sticking partially open and needs to be replaced if you wanted a 195*C.

PS: In *F the typical 195* operates closer to 200*F. It's a 12*C difference, not 12*F based on the number of real world tests that I have done. The t-stat's rating, is just a rating, they operate closer to the values I have given. And I have done 100s of runs with Diacom on a variety of vehicles/t-stats.


[This message has been edited by Glenn91L98GTA (edited September 26, 2001).]

 

Thanks, Ill look at that.

The operating temp of a typical thermostat is too varied depending on manufacturer (and tolerances which are quite wide), application, conditions, and even what the CTS thinks it sees to peg a number on it like that. I'll check and see what I get but I remember the car running at around 183-185 according to the CTS.

You have entirely too much time on your hands if you are studying thermostat temperatures... You know that right?

[This message has been edited by madmax (edited September 26, 2001).]

 

Oops, double posted

[This message has been edited by madmax (edited September 26, 2001).]

 

Max, you are correct about "variations" with T-stats. As for "studying" T-stats, if you want to be "tight" on the controlling of the fans, you have to do a detailed study.

I turn my fans on only a couple degrees above it's normal operating range. I am sure that if I through in a "Canadian Tire" T-stat that I may very well alter my fan settings cause most likely that T-stat is going to vary within a couple of degrees of my current GM T-stat. If it is a couple degrees lower, then I can "tighten" my Fan On/Off temps even more, conversely, I may have to raise them a couple degrees or my fans may never turn off.

I have one buddy, and his 180* runs typcally 76-78*C and he turns on his fans at 80*C. Mine typically runs 78-80*C and I turn mine on at 82*C. His settings won't work on my car as my fans would kick on in the typical operating range.

I have found that running "tight" like that, along with optimizing the spark (with a capped Knock Retard @ WOT of only a few degrees) keeps my car VERY consistent performance wise; no matter when I start my car (cold, hot, warm engine) or ambient air temperature. And that is my principal objective - to keep the car running consistenly (along with maintain good driveability and smoothness).

 

I just wanted to say I am very very confused now. I put the 180 stat in today but all these people saying not to makes me wonder what to do. I am getting my EPROM programer on Friday. What should I change in the TunerCat software for my 180 stat?

------------------
1989 Iroc-Z 5.7 350, Blue, T-Tops

Lightly Moded:
Headers, Rebuilt B&M 700R-4 tranny, Higher Stall Torque Converter, Airfoil, K&N's
-- Blue LED Bakelite Dash
"Just some 17 Year old spending every dollar I make on my car."

 

Glenn, what about the IAC learn on a 1990 SD car? The reason I ask is I have been chasing a weak idle at full operating temperature and I have a 180 t-stat. Thanks.

------------------
1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, MSD coil, 180 t-stat, Bald Eagle tires,
Hypertech fan switch, Accel 23# injectors, Holley module, ported plenum,
Ported Daytona Yellow stock base, Moroso valve covers, other stuff,
Streetdampr, Ruger P95DC, hot wife, new oil filter, !cats, !TBC, !AIR.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."

 

Jethro, SD is the same, just a different location. x'869B for IAC Min Learn Temp (stock 87*C or 188*F) and x'869C for IAC Max Learn Temp (stock 103*C or 224*F).

SD has even more dependence on the proper CTS, but when you "tweak" your VE tables on SD, just remember that it is for a specific CTS. If you change later, you will find your VE tables will need "tweaking".

I strongly encourage you to get the $8D.HAC and study it thoroughly. There are many tables that are affected that TunerCat has not yet defined. I have informed TC about the IAC Learn temps a while back, but I don't know if TC has modified their TDF yet. I am constantly modifying my TDF, so I have defined things that TC hasn't released yet.

89 Iroc Z, DON'T be frightened about prom burning. What we have been trying to tell everyone is that there is NO big mystery to it; ANYONE can do it. We are all learning at the same time; just some of us have been their sooner.

The $6E is remarkably similar to SD....more so than I would have ever imagined. I have been purposely working on a greater variety of cars/ecms to see the differences and similarities. From these different ECMs and eproms, I can see various approaches GM took to certain cars. Reviewing the newer ecms for spark can be interesting.

All of this is why I encourage people to get into their prom burning even before they make a single modification. I lived with a lot of "quirks" with my car for many years, thinking >.. it's just the way the car is. But once I got into eprom burning, I found out that it was something the ecm was doing and I COULD do something about it.

A great example, I always had to live with a "clunk" when I shifted my car from P/N to "in gear". I just thought it was the slopiness of the transmission or rear end; even though I had it at the dealership many times (when the car was new and on warranty) to try and fix with no success.

When I got into prom burning, I noticed there was a "RPM Add" for Park/Neutral of 100 rpm. I lowered it to only 25 rpm add, and amazingly, my "clunk" disappeared. This is just one example of the many "quirks" I have fixed on my car. How about the TC locking and unlocking when you are going over a series of rolling hills? Fix that also by engaging the TC Unlock Prevention speed at a lower MPH (stock is 75 mph, I set mine to 41 mph).

But probably the BIGGEST complaint I always had about my car was the "feels like a dog when the weather is hot and I just restarted my engine". That can be fixed by a combination of "tweaks" (Spark Advance and controlling the Knock Sensor, turning on the fans as soon as I go 2-3*C above my typical operating temperature, neutralizing the "Octane Retard Routine" and modifying the MAT Inverse Delta Temp table to work properly with a relocated MAT from -10*F to 120*F). Now my car never has that "doggy feeling" when you boot it and the engine is hot. Feels the same hot or cold now...like it should have from the factory.

 

This thread is the one that interests me the most about the thermostat debate. Vader or anyone else, can you tell me if the same temps, etc, apply to the tbi equipped cars? I would very much like to know the min temps for my car as well.

 

Reading through this topic has me thinking I should be putting in a warmer thermostat. Currently I have a 160 deg but I may duck down into the shops today and buy a 180 to bring it back closer to the stock set-up.

Have the fans come on at 183 deg F and turn off at 178 F to keep it running at the 180 mark which looks like a good temperature reading through these posts.

But I was wondering what you people have your fan speed enabled at? The stock 1992 Chip I use for my 86 has that setting set at 35mph.

Wouldn't that cause the fan to come on once you go over 35mph even with the temperature below 183 F when your fan is supposed to kick in?