After pondering where in the tech board to put this question, I figured this question is still appropriate in PROM tuning so here goes... I hooked up my ALDL cable and did some real-time monitoring of sensor behavior for 30 mins in my drieway at an idle. The most interesting observation to me was the operating temperature range. I noticed the temps run up to about 195 and then drop back to about 179 then repeat. I have a 195 thermostat installed so I assume this means that is the temperature at which it opens. I was just a bit surprised to see it go down as far as 179. The obvious mechanics are that the thermostat is at the top of the engine and if it opens (in my example) at 195, by the time the coolant from the radiator gets up to the t-stat, the overall temp has potentially dropped to as cold as the temperature of the coolan in the radiator. (?? is this logic accurate??) Anyway, the reason I post it here is becuase Im concerned that this operating range is low for ECM tuning. Is this normal? Will it cause any issues when I start tuning with EBL flash? Does the situation I describe above sound normal, or could I be looking at a faulty t-stat? Thanks in advance!

What you are seeing is the action of the thermostat, some have small holes drilled in them to bypass some coolant all the time.

At 179*F you are high enough to stay out of the cold enrichment mode, unless it has been changed.

I believe it is set at 175*F in a 1989 6E ARAP bin.

Thermostats are not all the same, mine is a 180*F and it heats to 200*F even in sub zero weather.

What brand is it?

I believe its a Stant. For $10 or whatever I'm inclined to change it just to be safe and see what happens.

I've seen cycling in temp's that slowly go back to a 'solid' temperature. It's doing what you described, with the t-stat opening/closing. So on the 1st round you get pretty much solid cold water rushing back into the block (temps drop a lot), next time around the waters a bit warmer (temps don't drop as much), and so on each time, until you more or less get a solid mix.

Did you remember to drill your stat before installing?

Drill it?

Popular thing to do (I do it!) is drill a couple of 1/8" holes around the edge of it on the flat area. Let's the air out as you're filling, plus let's a small amount of fluid through so you don't seem to get the temp spikes as much.

Works for me. YMMV.

wow, never heard of that trick before. The only question/concern I'd have is that this technique would potentially result in longer warm-up times espeically for a vehicle in the North East like mine where winter doesnt get much above 20*F for 3 months at a time. Anyway, I'll keep it in mind for a summer setup.. THANKS!

Heh-I can totally relate on the winter aspect-I'm in southern Canada.

It hasn't topped 15c here (for more than a few hours) in the last 9 months!

It does slightly increase the warm up times, but at least I don't see the huge temp spikes I used to.

Some people worry about thermo shocking the hot engine with cold coolant. That is why they drill the holes.

I think the air/steam bled is the best reason, but thousands of thermostats don't have them.

I prefer to put one small hole in the thermostat. Between 1/16" and 3/32" and let the thermo do it's job. The hole is just to bleed the air out.

Some of the older thermostats I have around here have a small notch cut in the center opening. This is a factory added notch for the purpose of bleeding air. It is also on the small side.

RBob.

I've been drilling t-stats for a long time now. As long as you dont over-do-it it really helps stabilize temps. The air-bleed you create is also very beneficial when filling fluid, and REALLY helps is you run into an emergency situation trying to add water during an overheat-boilover.
since using drilled t-stats I have not seen bouncing temp gauges on my cars like I used to.
And for those people in cold climates, it still works fine, just make the hole smaller, and if you still overcool put a piece of plastic or cardboard in front of part of the radiator during cold months. Have you ever noticed semi-trucks with covers over the grill? They open them up to however much airflow they need depending on the outside temp.