How easy is it to change a thermostat on a 1988 iroc with the 5.7? Also what temp thermostat is best to run?

 

being in new jersey you gotta deal with kinda cold weather, right? a stat (unless you have to tap and die the intake like i did my first time ) takes about 15 minutes. you unhook the hose goign into your intake manifold from your radiator, take out the stat, put some RTV on a gasket, pop the new one in, and tighten the bolts. back to the previous statement, a lot of people actually run WITHOUT a stat during the summer. make sure you put it back in when the cold weather starts back up or its going to take forever for you car to warm up. i use a 160 stat during the winter, no stat during summer. i found this is the setup most people around here use as well.

 

I use a 180deg stat. always. I also have a jet fan switch so that helps.

 

Living in NJ and having TPI I would go with a 180*. When you start to go lower it may mess with the computer.

 

Quote-- a lot of people actually run WITHOUT a stat during the summer. make sure you put it back in when the cold weather starts back up or its going to take forever for you car to warm up. i use a 160 stat during the winter, no stat during summer.--Quote

Thats not a bright idea!! That will cause overheating problems more than if you had a low degree stat. The thermostat slows the speed of the coolant down so the radiator has time to cool it off (this is not the main reason for having one). If there is no stat in the housing the coolant will flow to fast for the radiator to cool it down. Just stick a 160* in there and you will be fine. Also make sure your fan cuts on at about 180*.

 

I also would recommend the 180* t-stat for your car. The lower temp one will not lower the operating temperature, it just takes longer to warm up as the coolant starts flowing earlier, which hurts the efficiency of the engine. A friend replaced his 180 with a 160 and dropped 3 mpg around town, while it ended up running just as warm as before on the highway.

 

all i know is a lot of people around here (dallas) run summers without a stat and have never heard of one of them overheating. and i havent gone over 200 since i put in my 160 stat

 

Glad for it. Just stating a known fact. Read any HP book or ask a reputable mechanic and they will tell you the same.

 

Running without a thermostat will only cause overheating IF the flow is too fast though the engine/radiator. Usually doesn't happen in a stock engine. Running an engine too cool isn't good for it. The oil also likes to get warmed up good to burn off the crap in it. If your fan kicks on at the normal 220+ temp, I would just stick with the stock 195 thermostat. Going cooler won't help unless your fan kicks on sooner. If you want to go down to 180, get the fan to kick on around 190.

 

i'd recomend using a 160, but a 180 will work fine also if your concerned about heat. do not use rtv on the gasket. this is the point of using a gasket, to seal it. easiest way on the tuned port to get the thermostat out is take the 4 bolts loose for the throttle body and keep it hooked up. this just allows it to slide out of the way, then remove the two bolts for the thermostat housing. remove the housing from the intake and remove the thermostat. clean the surface of any gasket material with a razor blade and clean it of antifreeze. from there out, just put it back together with a new gasket and new thermostat. you'll probably lose about a quarter gallon total of coolant.

 

In your 5.7 MPI the best thermostat is the factory spec.The reason behind that is the engine must reach a certain temperature to go into closed loop operation where the computer makes adjustments based on O2 sensor values and other variables.Until that time it is in open loop where preset values are used .This would probably affect your emmisions and gas mileage more than anything else.

 

hello cam84358, so just where are you saying closed loop goes in? i'd really like to hear this.

 

Oxygen sensor 600F,coolant temp 160F.Keeping the coolant temp near 200F reduces exhaust emissions thats why mfrs use the hotter stats .

 

Follow Zippy's advice, taken of the TB is the easiest way on a TPI.

Hmmn, anyone else notice the other "old wives tale"?

 

so, closed loop doesn't begin until 160 degrees is what i'm reading. anyone have an opinion on this?

 

Closed loop starts when the coolant reaches about 105 degrees. This is relative however because O2 operation also comes into play. I have found that on my 5-7 when the guage is a little over a hundred degrees I will get TCC lock and idle is pretty near normal. I have tried EVERY temp stat, with and without holes drilled in them and I have found here in Pennsy that a 180 is a nice all around temp. This temp gives you good driveability and keeps the engine a little cooler. If you don't mind a little cooler heat try a 170 stat. Remember one thing, I does not matter WHAT temp stat you run, you get stuck in shore traffic and that coolant temp will go as high as the fan temp switches permit. I run a JET 205 turn on fan switch with a 180 stat. It will turn on the fans at 205 and shut down at 185 degrees. If you want a little more time before fan operation, use a 170 and it will buy you a little while sitting at a light before fans come on. Also the 180 stat keeps the operating window of temp fairly small after warmup. I personally believe this is probably better for the engine overall. Danno

 

at 105, the engine is not quite yet in closed loop, but your close.

 

The primary reason for changing your thermostat is your climate.

The secondary reason is you disagree with GM's choice of recommended operating temps.

If you live in an extremely hot climate you will overheat, even though all influencing factors are correct, especially when you run your A/C.

The 195° thermostat was installed as an emissions issue. And it was a "one size fits all" solution. It was far cheaper to heat your engine up to to a ridiculous temp to burn excess emissions than it was to design a more sophisticated emissions system.

But one size doesn't fill all so if you wish to lower your operating temp to a "safer" level you should match exactly to your climate and that will be the right choice.

195° ~ If you live in the Artic Circle.
180° ~ If you live in a predominantly cool climate.
170° ~ If you live in a predominantly warm climate.
160° ~ If you live in a "hotter than hell" climate.

I think everyone could benefit from changing from the joke GM played on us to a 180° then let logic take it from there. If a 180 works then stay there... if not.... progressively move down. The stats are cheap enough and easy enough to change to zero in on it.

~~~~~~~~~~~~~~~~~~~~
Red 86 T/A 5.0 TPI (LB9/WS6)
~HyperTech Cap/Coil/Rotor/AFPR
~Derale Adjustable Fan Switch ~ 170° Stat
~Flow Matched Injectors ~ K & N Air Filter
~Ported Plenum ~ Pirelli 245/50/16
~SLP TB Airfoil ~ All Else Stock

 

135?

 

To get the exact coolant temp data, you'll need to look at the EPROM and verify what's coded in. I believe my Helms says 103*F, O2 generating a crosscount or outputting sufficient voltage..don't recall, and "some" period of time. This is what's required for closed loop fuel control. There's other variables too, EGR diagnostics enabled temp and maybe a few others..that go active at higher coolant temps..in the 150-ish F range but are not directly affecting A/F ratio.

 

Sorry, no opinions, only raw data. The factory EPROM in his 1988 model has the following CTS paraameters for the associated ECM functions:

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)

As you can read, the ECM must see the CTS reporting at least 176°F to enter what most of us would loosely consider "Full Closed Loop" mode. Fuel trim and enrichment aren't at the factory designed full operating temperature offsets until that point. That's why a 180° is probably safest with an unmodified ECM.

Not my opinion, just my data....

 

very good reply posting vader. more than i wanted to type in, lol. basicly by 133 F the engine has it's own decision making capabilities and before a 160 thermostat opens, the major functions are all in order. for it's best operation, it doesn't have full capability of adjusting and switching on and off items until 176 although i've found the fuel curve below that to be sufficient although not perfect. running the 160 would get the e.g.r. function, t.c.c. function, highway mode spark, block learn enabled, and power enrichment. it gets you your basics, but the 180 would get you the rest of what the computer wants especially if your going for emissions or consistant numbers. either one will work, just with different ideas behind the other.

 

You have been schooled by Vader. That was impressive.

 

I agree with Vader that a 180 is an excellent choice for the majority of owners. It gives you a 15° drop in operating range with little chance of overcooling.

But what I do see consistently is the tendency to think that the thermostat rating is a "rigid" number.

For example a stock 195° stat begins opening at 195 is fully open at app. 206 and closes at app. 188. That means our thermostats operate in a range as do our engines.

Because we install a 160° thermostat doesn't mean that our engines temp will stop climbing at 160. In an extremely hot climate it won't matter what stat you install you will reach the last ECM based temperature decision of 176°. But install the same 160 stat in a sub-zero climate and you may have improper overcooling.

On a stock 86 T/A the cooling fan comes on at 234° and if the stock 195 stat would hold "rigid" temp then we wouldn't even need our cooling fans. How many times have our cooling fans come on ........ and thats 39° above the thermostat rating.

My point in this rambling is even the lowest rated stat, except for the most extreme conditions, seems it would meet the ECM criteria.

Correct me if I wrong........ and Vader......... go easy on me duuuuuuuuuude.

 

this is a very good point mike, unless you just get right on the highway your likely going to reach an engine temperature of over 176 even though you had a 160 t stat since sitting in traffic would raise operating temps above the opening temp of the thermostat. using a 160 stat would just slow the rise earlier. using the 180 will only get you closer to the factory t stat temps in traffic and lower on the highway.

 

Excellent point Mike. A 180°F stat is a safe bet almost anywhere. A 160° is probably more appropriate where you are located, since there is very little chance of overcooling on 364 of 365 days.

If you look at the choices, a 170° is probably safe as well, but could be on the ragged edge in cooler climates. A 160° almost certainly would never make the required 176°F in a mid-western February at only 800' ASL. A 170° would probably never even make it on some of our coldest days, or in farther north climates - like up where those guys took our gold medal. So I generally quote the 180°F number to be safe just about everywhere.

As you said, 180° is already at least 15° cooler than the factory stat, and the addition of a fan control completes the package (thanks for the idea - mine is working great!). Without the fan control, the coolant will just continue to heat up to the 234° fan cut-in, regardless of the thermostat rating (unless it is VERY windy). With the combimation of the thermostat and fan control, the coolant temperature actually stays somewhat reasonable, but the engine still gets hot enough for good efficiency and relatively clean emissions. Going too cold could start to affect NOX on some engines, and might just cause other ECM "problems" as well.

Speaking of all that heat there, isn't it a really bad idea to store an older "sports car" in a hot, sunny climate? I know of a nice, cool, shady garage that is perfect for storing anything with a bow tie on it, and we all know how that red paint can fade...

 

Vader.... you are the kindest person I know to invite me to store my "old sports car" in your garage, I mean I wish I had more friends like you.

BUT, as you forgot, I am a fake. I no longer live in Hotter than Hell Phoenix, but moved to New Mexico and that Red T/A is just loving it here........LOL.

PS I'm working in a friends bodyshop so if that ol' paint starts fading out here, I got a line on that to. You can see by the picture I'm really roughing it here.........