I was talking to a fellow 3rd genner friend of mine, and he was told by (he says)a "five star mechanic" that running a lower stat in a smallblock will cause the oil to run too cold, causing the rocker arms to get blackened and other strange anomalies.

So, what do the masses say?

------------------
DR Stevens
Car #1:
1984 TA L69 H.O.
750 cfm Q-Jet reman. by Holley
700R4/Superior shift-kit
3.42 lim.slip
4whl disc
underdrive pulleys
Accel HEI Super-Coil
experimental dual snorkel /w/ hood louver some sort of weird 3" exhaust soon to be replaced
partial emissions delete
Car #2:
'91 Firebird/Formula LO3
K&N air filter
Hypertech Thermomaster Chip
more in the near future

 

That's why if you're running a colder stat you should change to a thinner grade oil. I used to run 20/50, but after changing to a 160* stat I went to 10/40. It is possible that running too cold will allow carbon to build up alot easier in the combustion chamber as it isn't as likely to burn off, but that's the only problem I can think of being possible.

 

I've run my coolant temp between 150 and 160F for several years and haven't noticed anything like that. Also my coolant temp has very little effect on my oil temp.

 

The only time I've seen a lower temp thermostat cause any problem was on Ford 2.9/3.0/4.0 V6s.

I've had a couple of them come in with 160 stats and belive it or not, they won't pass smog.

I put a 195 in it and its all better.

The F.I. on those things needs 190+ degrees to be working correctly and cleanly.

As far as on thirdgens and most other cars on the road, I would run what ever you wanted. I think someone is pulling your leg.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

R.I.P. #3
My favorite quote about D.E. "He can see air"

 

And for a little more confusion...

There are some coolant temperature related parameters in the ECM programs, and the critical points are 157°F and 176°F. Going below 176° with a TPI and a stock PROM can cause some minor problems, mostly on the emissions and EGR side. Your E4ME car shouldn't care about that at all. At the same time, your E4ME car won't have the same fuel curve benefits as lowering the coolant temperature as an EFI engine, but you'll always have the benefit of longer engine life and lower chamber temperatures, allowing more compression and timing advance. Much below 160°F isn't beneficial, and a 170° or 180° stat seems to be a good compromise for year-round operation.

------------------
Later,
Vader
------------------
"I'm'a do Things My Way - It's My way or the Highway."
Adobe Acrobat Reader

[This message has been edited by Vader (edited March 11, 2001).]

 

There's a good rule of thumb which should be followed when considering going with a lower temp thermostat....if it ain't broke--don't fix it.

Now I know that goes against what makes "tinkering" with cars fun, but sometimes things that are as simple as a lower temp thermostat--maybe even possibly beneficial, will affect other areas negatively. So if your car runs steadily at about 190* or so (like my 91 Grand Prix) and never goes above 220*, why mess with it.

I know that in a '93 Dodge Shadow that I own, a lower temp thermostat will negatively affect the FI and idle when warm like Vader said......

That's the problem with computers in cars, you have a lot more areas you need to understand before just swapping things in and out.

That's why I've gone "old school"!!!!!
(I mess that up too though, so it doesn't matter )

 

On the SD TPI, I have found so many "hidden" little settings based on temperature it is virtually impossible to list. I recently found the IAC "learn mode" is affected and can cause it to go into "stay alive" if it is too cool.

Also "Stay Alive" is affected by temperature, along with your idle, your "starting" IAC number, etc. And, in all honesty, I don't believe I have found them all; that is how many things controlled by it.

Vader is right, that a 180* T-stat doesn't seem to "upset" the apple cart as much as the 160* does. Oh, a 160* will run and it will feel "torquier" at the bottom end, but this has more to do with the "cold start" routines than any actual power difference. In fact, you will find that you are generally running too rich.

This is okay if you have made some serious mods to your engine and NEED the increased fuel. But on most "basically stock" (ie. original heads/cam), you will generally running on the rich side anyways. GM designed the eprom like that (to be too rich).

The largest benefit to a cooler T-stat is a cooler intake, especially if you haven't bypassed the TB or relocated the MAT, as the MAT soaks heat from the plenum. But if you have bypassed the TB or relocated the MAT, then the benefit of a cooler T-stat is offset quite a bit. But now, with a bypassed TB or relocated MAT, you introduce other "sensor error" into the ecm which really needs to be adjusted to get the ecm to work properly and give you 128/128 perfection.

On a last note, I prefer a warmer engine because it also expands the metal parts a little more and makes the tolerances tighter. I found with a colder t-stat that I actually got higher incidences of knock retard. Now that I went up to a 180* t-stat, those knock incidences are less.

I have been taling with an engine builder and going over some of the observations I have made. Lke with a 180* t-stat I get more incidences of knock retard in the first 30 minutes of engine running than I do after 40 minutes of engine running...I can run 2-3* more spark advance after 40 minutes than I can in the first 30 minutes. And by "the first 30 minutes" I mean doing a WOT test afer 25 minutes of the engine running, not before.

 

I should add, with a 160* t-stat, this "operating time" never went away and I always got incidences of knock retard. With the 180* and 40 minutes of running, I don't.

 

Every car is a little bit different, and will respond differently. My carbed 82 likes a 180 thermo.
I've seen way to many people install a lower temp thermostat because of an overheating problem. If you car is running 210+, it does not matter what temp thermostat you have because they are open all the way.


------------------
82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

 

That's a relief. I run a 180 stat in the L69, and it seems to like that much better than the 195. I also run a Jet fan switch which seems to turn the fan on around 220. Between these two units the temp seems to hover around 190-200 most of the time. The switch that I had before didn't kick in until 238!! 190-200 should be optimal for my engine, shouldn't it?

------------------
DR Stevens
Car #1:
1984 TransAm
305 HO (L69)
750 cfm Q-Jet reman. by Holley
K&N filter
700R4/Superior shift-kit
3.42 lim.slip
underdrive pulleys
Accel HEI Super-Coil
180 stat/hi flow water
pump/Jet fan switch
dual snorkel /w/ hood louver
3" exhaust of some sort
partial emissions delete
Car #2:
1991 Firebird/Formula
305 TBI (LO3)
K&N air filter
Hypertech Thermomaster Chip
more in the near future

 

I put a 180 in my car cause in the summers it gets to the 90's but in the winter to the -'s so 180 is near perfect for my area.

------------------
89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR

 

i ran a 160 for a long time, and i observed similar occurances in my EGT as did glen with his knock counts

i found 160 made for inconsistent egts and performance

ive since gone to a 180
there is so much stuff in the prom thats still in warm up mode around 160 that its not really a wise choice
I dont even think its a wise choice on a non computer controlled car

Can anybody show track times that show that running at 160 was faster than at 180?
I think it will show more inconsistent times at 160 if anything

 

Pablo,

A guy I work with used to run a Gas Chevy 2 in the late '60's and saw Grumpy Jenkins at various tracks all the time.

He once had a discussion with "da grump" about operationg temps - and here is the short story.

Jenkins related that he tries to keep temp up to 200* F for these reasons: (and guys, this probably needs to be re-examined if you are running a smog/TPI/computer motor....)

Builders do not assemble engines hot - in fact, they're cold during assy.

This is why the pros actually heat the block and torque plates right before machining (there was an article on this in one of the hotrod rags last month).

If you machine the block cold, as almost all of us will, you'll need to remember that factory piston clearance specs as well as ring end gaps are based on cold motors. Da Grump ran loose, hot motors......they atomize fuel better (read carbed cars here), seal piston-to-wall clearances, and tighten ring end-gaps.

For street motors, I've always stayed on the small end of the spec scale for ring end-gap, piston-to-wall clearance, and bearing clearances. It makes for a tight motor that seals compression better, and the bearing tolerances being tight makes for a durable engine.

Do not go tighter than minimum factory spec on bearings, or you'll hinder the .002" rule for keeping parts filmed with oil. I use .012-.014 ring end gap on top rings with .014-.016 on the second ring (for 4.03" bore)

This stuff is far from pure science, but seems to work on carbed cars very well. Temps are 170-180* cruise, never to exceed 200*. A 160* cruise will not atomize fuel properly on a carbed car, and will not provide for good cylinder sealing after the break-in period on any car. It's just too cold.

Related to this, I'll probably use Sealed Power rings on the 406 this summer. I have to get the manufacturers' opinion on whether or not they will tolerate 11.7 to 1 compression first.

Again, take this info with the knowledge that it's only MHO, and TPI motors may like to run warmer than 170-180*, I just don't have much knowledge on late-models. FWIW, I run a 180 stat in my TPI with both fan switches kicking on at 200*, and this seems close to optimal on my 91K mile L-98.

BOR

 

FWIW, I found that my E4ME car likes 180 better than 160. The fuel consumption and general driveability is much better, and it actually seems to have a little more power (probably from better atomization).

Rule #1: Don't go too cold on a wet flow induction system.

 

Finally some smart people on around here, I've lost count of how many arguement I've got into about a lower stat giving increased performance. It might *feel* torqueier on the low end, and the only benifit is from a decreased manifold temp, but if you have a CAI setup or even ram air, a colder stat will hinder performance. I've found this out toying around with stats, I have CAI and I've noticed increased performance (everal tenths higher MPH) with my 190stat than with a 160 and 180.

 

"Impossible to list" - but I'll give it a try anyway. At least for some of them:

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)




------------------
Later,
Vader
------------------
"I'm'a do Things My Way - It's My way or the Highway."
Adobe Acrobat Reader

 

I always thought a cooler t-stat meant less detonation? I run a 170 and it usually runs at 176degrees. I HAVE noticed ALOT of detonation. Should I run hotter?

 

the opposite is true, i found my car had more tendency to detonate when cold than when at operating temp

i guess the denser air creates more cyl pressure and since its cold and dense the fuel doesnt atomize well so in the cyl you might have some extreme (more extreme than usual ) differences in AFR

thats my theory on it from all ive read

and good post BOR

 

Vader,

Also IAC learn temperature, Stay Alive temperature, MAT vs CTS, IAC counts vs CTS, Highway Mode AF ratio, TC locking temperature (it has its own separate from closed loop)... plus more still ... but it is late and I'm tired...

This is worst than counting sheep...zzzzzzzzzzzzzzzzz

[This message has been edited by Glenn91L98GTA (edited March 13, 2001).]