in the last two weeks i've put on my CAI, Magnaflow, and high-flow cat. i also put in an intense 180* stat, and my temps are noticeably lower while cruising on the highway. however when i get on it hard for a few minutes at a time, my temp goes from hovering around 180-185 to 200 or even 205. this also happens when i've been driving around town for a while and then pull in a parking lot and leave it idling. the temp peaks at 205 or so, then comes down. i'm assuming the fan kicks in at that point. is it an EGR issue? is the motor working harder and generating more heat? just looking for someone to shed a little light on why i have higher temps than i ever did with a stock car and 195 stat.

If your EGR is faulty, it can cause it to run hotter (EGR flow causes a reduction in combustion temps, not an increase like you might think).

Mods and 'spirited' driving can affect it too, but for the most part, the 180 will only help you as long as you have air flowing through the radiator.

At this point, considering you're now modified for performance, I'd suggest drilling two 1/16" bypass holes in the stat and using a high speed fan switch to force the fans on earlier.

-a few notes from my experience: Most certainly, "spirited driving" will introduce more heat into the system. And during "town driving," -especially after a "higher b.t.u. run" your thermostat will be "out of the picture," no matter what temp thermostat you are using. -(assuming summer temperatures)

By "out of the picture" I mean this: After your cooling system has reached the temperature opening point of the thermostat, (and usually after a couple of open/close cycles) the thermostat remains open. At that point your engine temperature will be determined by the temp "set point" of the fan switch. -you will probably find it to be around 200 or 205.

Now, there are a lot of variables involved. Normal "town driving speeds", especially stop and go in the summer time, do not provide enough air flow through the radiator to remove enough heat. Therefore, the electric fans come on to assist. And once that temp drops sufficiently, the fans go off again. And this cycle repeats over and over.

Why is the fan switch set temp higher? Because if it wasn't, you could have a condition where the fans would be on at the same time the thermostat was cycling within it'* operating temperature tolerances. Your cooling fans would be attempting to bring reduce the engine temp at the same time the thermostat has the coolant flow stopped, increasing the temp. The most likely result would be that your fans would run all the time, after the engine reached normal operating temperature.

As a side note, I think research will show that the only reason to drill a hole (small hole at that) in the thermostat plate was to bleed off any air that may accumulate on the back side (engine side) of the 'stat. Air is certainly not a good conductor of heat, and consequently there were some cases of the engine temp getting pretty high (way higher than the 'stat temp) before the stat opened. The small about of coolant bypass that this hole creates helps to make the stat work smoother. The original purpose of the hole WAS NOT to provide additional coolant flow.

If people are concerned about additional flow, then I would suggest using a "high flow" stat. I haven't looked for one for the 3800 applications, but I have used them on high performance small block chevy stuff.

mine heats up to 195 every now and then when i am sitting still at a light with the air on...

-another variable- I think you'll find that at least one of the fans runs continuously when you have the A/C on. -so, depending on conditions this may very well keep your engine temp from climbing on up to the point where both fans come on.

(probably more info than ANYONE wants to know.) BTW, you can try this out in your driveway, with the hood up, and engine running, but not yet up to normal operating temperature, switch your A/C on, and notice a fan come on. Then turn the A/C off, and the fan shuts down. (-may be a few seconds delay each way, -don't remember exactly)

i have had my bonnie for just under a week now and it has yet to reach the 200 mark, even in 90 degree heat driving around the city. seems a bit unusual, but i'm not complaining.

The bottom line is this:

No two cars are alike (I know, you've heard it before)..... BUT, to back that up, I've seen identical cars (SSEi'* for example) run anywhere from 190 MAX to 230 under normal conditions. Many factors come into play. How clogged is your radiator core? Is it just the coolant core, or are the other TWO (yes, we have 3-core radiators for Series 1, with the Engine oil, Coolant, and Trans all flowing through it) in good condition? What'* the condition of the water pump? Water passages? Is the transmission producing too much heat?

There are so many variables, the odds of only one of them affecting your problem may be VERY remote. It'* likely a combination of factors. My best advice:

1. Have the cooling system flushed professionally.
2. Change the ECT sensor and replace it with an AC Delco unti (OEM).
3. Install a drilled (two 1/16" diameter holes) 180° thermostat.
4. Install a SECOND trans cooler or replace your stock cooler with a Thermostatically controlled unit with larger dimensions (4T60E cars 92-96 only).
5. Install a fan override switch for the summer months.

This combination WILL lower your operating temps, but it takes a concerted effort to make a difference. Performance engines run hot. That'* what we've got. To cool it off, you have to look at the big picture. Even a lower thermostat by itself will do nothing for you, unless you have constant airflow through the radiator.

In the summer, the 4T60E trans will typically run hotter fluid than the temps of your Engine Coolant. The net effect is trans fluid HEATING coolant in your 3-core radiator. Cool the ATF down, and use that to help drop the coolant temps. Make sense?

Ok I need to weigh in on this one. I just installed a "high flow" cat and I swear my engine runs hotter than it ever did. It used to always sit at 215-220 on the gauge, no matter what.

Now, when I am moving it still stays on the 215 to 220 mark.. But when I idle, it zips all the way up to 250, the fans kick on and drop it back down to the 220ish mark. And it cycles this way. Now maybe the gauge reads a bit high, and the 250 indication is really more like the 220 setpoint for when the fans go on. It is definitely behaving differently.

Why would a freer flowing exhaust run so much hotter at idle? Scavenging effects?? mixture problems? I expected lower temps. The cat seems to be flowing fine because the performance is ok. And I wonder just how much different the new cat is anyways, since the stock cat was quite big.

Needless to say I don't like this development. Or is this just some diabolical coincidence meant to drive me insane? I am starting to wish I shelled out the cash for the GM converter. Sometimes they know what they are doing. Help !!!

I run at the line after 200, usually, which really sucks because it becomes quite nutless at that point. What is that temp anyways the gage confuses all my feiends and myself (100 lowest, 200 middle, 280 peak what the heck?)

Ok yes I never noticed that the gauge is not a linear scale. When I was saying I hit 250, I meant the first mark after 200. If I treat that last half of the scale as linear (who knows?) then I should probably say that I am now hitting 220 degrees, where before I was always just a tad above 200. So maybe the scale goes 200, 220, 240, (no mark in the red zone), then 280.

But I still stand by my claim that the engine runs hotter with the free-flowing CAT. The only other things I did at the same time was remove the rear plug wires and remove the O2 sensor so they wouldn't get damaged. And I checked the firing order and that is ok.

The engine just gains heat a heck of a lot faster than it ever did, at least at idle. It gets to where the fans need to kick in fairly quickly.

I hope some of you can comment on what might cause this, what engine parameters might have changed.

Also, Will, if you are reading this thread, I wanted to pass something by you, that is sort of related. Instead of putting in some secondary thermostat to turn the fans on sooner, what if there was a simple circuit (I haven't really studied it yet) that could be inserted between the ECT and the PCM that would make the PCM think the engine was ~15 degrees hotter than it really is. This would kick the fans on earlier. The question is, how would it affect the general running of the engine? Or more specifically, how critical is the ECT to the various mixture and timing parameters? Would 15 degrees screw it up?