Originally Posted by ymeski56

If you warm your engine up to it's normal operating temperature, then do the KOEO error code scan. If you receive a code specifying the ECT sensor is "out of range", that points to a T-stat stuck open or failed fan clutch if temp is low at idle, but the temp increases while driving.

You can also buy a Laser thermal reader for about $20. at Harbor Freight & tools, & aim it at the Thermostat housing while at it's normal operating temp to get your actual Op. temp. Great for I.D.ing a misfiring cylinder as well as determining cooling coil efficiency, like for the tranny.

As your operating now, if Norm. Op. Temp is not reached, the ECU will not enter closed loop function, which keeps you in "over-rich cold start purgatory" (no ECU assisted fuel trim). Average attainable MPG = 9-10 mpg/ city & hwy.

W/ your cooling system history, the T-stat is a good, cheap bet even w/o an ECT code backing your play, but check your fan clutch function too.

Originally Posted by SouthernPride

Thank you and all the rest of the replies. I'm no mechanic by any means but I try to do what I can because I don't trust most other people messing with my vehicle. Pressure tested today, it went down about a quarter pound or so. So it's safe to assume that a thermostat can be stuck wide open and the gauge can still go up and down? Perhaps it's time to change it out. Cleaned everything last summer, will check it all again this weekend. Regarding the TPS, no coolant was near it but as far as bumping it, I guess it's possible but I certainly don't remember doing anything like that and if I did it had to be a gentle bump otherwise I would remember it. Are these things -that- sensitive?

Originally Posted by ymeski56

If everything "seems" to be fine works for you. That's kinda like not checking your oil, because you might need to add some. Personally, I bought & use one of these. Digital Numeric display w/ memory = $22.77. (optional cable is to allow you to sit behind the wheel during scans, but not required)

Or you can default to the more popular method of waiting until you actually notice your MPG is taking a dump or you notice a performance decrease as most people do.


http://www.handsontools.com/Equus-In...ol_p_5574.html

Originally Posted by ymeski56

If you warm your engine up to it's normal

As your operating now, if Norm. Op. Temp is not reached, the ECU will not enter closed loop function, which keeps you in "over-rich cold start purgatory" (no ECU assisted fuel trim). Average attainable MPG = 9-10 mpg/ city & hwy.
.

Originally Posted by djhives

Ymeski56,

Heres a question for you - becasue Im still gotta get that scan tool you showed me -- but Im not sure if im operating in closed loop mode -- its a E150 5.0 so its much heavier - but I get that 9-10mpg you mentioned - So im not sure if the truck is ever getting to open loop mode after warm up (the temp guage does go to the middle of 'normal' on the guage..)
The ECU must be told you've reached Norm op temp (approx.184F) via the ETC sensor before it goes into closed loop. Your "stock" t-stat is rated at 195F for the purpose of reaching closed loop temp quickly & remaining above that temperature. You also have a Coolant temp sender, however this only serves your temp gauge & no relation to the ECU.
ANYWAY - question: Once you start a cold 5.0 it idles high for a while, then kicks back down after about a minute to a 'lower' idle - is that 'kick down' to that low/normal idle an indication of the ECU running in open loop mode or is that seperate from the idle speed? If everything is functioning correctly, closed loop function will be associated w/ a idle RPM of 650-675 (302/351 A/T's). A normal op temp (closed loop) idle above that implies something else is amiss. Except when excessive temps are reached, when the ECU may increase idle rpm to compensate.

Am I making any sense?
Yep!
basically what im asking is, when I do a cold start, then the idle kicks back down after 45 seconds did I just enter open loop mode??
Nope!
THNX!!

Originally Posted by djhives

also can I purchase that OBDI reader in an autozone or advanced? Or is it online only?

THNX

Originally Posted by ymeski56

Your welcome!

To clarify, normal Op temp is considered 195F. However closed loop (w/ few exceptions) begins when 184F approx. is reached.

There are situations when lower temp thermostats are advantageous, but for your stock set up, you'd stick w/ the 195F thermostat.

Originally Posted by djhives

Duhh -- now that I think about it I knew that answer... closed loop typically begins when the engine temp is at a certain level OR (as on some other cars) when the O2 sensor reaches a certain temp...


anyway Ill get that reader and see what all this code-pulling fun is about!

Originally Posted by djhives

Perhaps your thermostat has always been stuck open and your old radiator cooled at only 30% (ie ran hot) therefore between your half backed radiator and a wide open themostat you were 'normal' most of the time.

Now you got a new radiator and it cools 100% but your t-stat is stuck open so now you're cooling too much...

Whens the last time you changed the t-stat?


With cooling systems its like a can of worms -- replace one thing and something else in the system is exploited.

I test drove a 90s vintage miata yesterday - I have 2 already - I redline mine every shift --- when I drove this womans car I redlined it too the entire test drive -- when I came back coolant was leaking from the hoses! She had never drove that car in high RPMS - as a result the hoses got 'used to' low pressure... introduce high pressure and you exploit a leak... in your case you might have exploited the fact that your tstat is stuck open!

There are cooling lines going to your TB which may or may not affect your idle if they are too cold.


Did you clean your IAC latley? That fixes low/stalling idles.

Did by chance you bang your TPS when you were funmbling with your TB? Did you get the TPS wet with coolant somehow?