UFM82

OK, this is a problem I've never experienced before and I've already taken steps to resolve it but...
I got tired of having sucky heat in my 2001 S-Crew. This truck takes FOREVER to warm up but once it gets there it seems to be OK. I thought maybe after 15 years it was time for a new t-stat even though the temp gauge reads exactly where it has for the life of this truck. So I installed a new 195° t-stat. Well, it didn't make squat difference in the heat or how long the truck takes to warm up but I developed a new issue. If it's really cold- like in the 20's or below, the truck will run fine until the t-stat opens. I see the gauge needle rise and before it gets halfway up the truck will start to buck and surge, especially when sitting at a light. It will stall if I don't keep a foot on the throttle to prevent it. Once it fully warms up it runs great like it usually does. Doesn't do it if it's not below 30°. I noticed on the Motorcraft t-stat a little "bypass" hole with a simple valve in it that the aftermarket unit did not have. My guess is that the new t-stat opens and dumps a load of cold water in the engine which hits the ECT and makes the engine surge. The Motorcraft t-stat allows a small amount of water to flow through, moderating the change? That's all I can guess.
This started last year after I changed the t-stat and did it like clockwork last winter. We've finally gotten cold here in Ohio and the last two mornings have been a PITA getting the old gal to work. I have a new Mortorcraft t-stat sitting the in front seat awaiting a new home tonight so I'll see what happens.
Any other ideas? Oh yeah, my heat still sucks...

Mr. Beef Gravy

Wow, that is the most violent tstat I have ever heard of. You are correct though, it should have the weep hole in it. But I don't thing that would cause such a dramatic effect. My guess is the aftermarket stat is junk and doesn't open correctly. I have never heard of one making the truck buck though. That sounds like it is starving for air. I would check your vacuum and pcv lines.

That being said, my truck and my co workers truck take quiet a while to warm up. We both go and warm them up for 10 min and by then they are luke warm, after another 2-3 of driving and they get hot. Mine has been that way fro a while. Today took a little longer as its in the teens.

patbob

I was thinking open/closed loop and vacuum or intake leak too, until you said it runs fine once it fully warms up. I think you're right, its opening and letting a slug of cold water in, which rapidly cools the ECT and confuses the computer. I'm surprised you don't see the temperature needle move as it happens, but maybe it's too damped or that sensor is someplace else.


Just for grins, it might be interesting to plop the aftermarket one into a pot of water and warm it up. I'll bet you find that it practically snaps open and closed as the temperature varies, rather than smoothly opening and closing. Its probably mechanically binding up.

mbb

My needle doesnt move for about 5 min and several miles in traffic in morning with the 195 tstat.

I had a motorcraft 180 a shop put in that was defective, engine coolant ran about 170-180 in warm weather ( apparently I dont lack for radiator). Then it got cold around 35-40, and coolant didnt get above 164. Motor gave code for too low temp for closed loop, and wouldnt complete a drive cycle (has to be at least 170). Even motorcraft fail.

Razgriz

My truck starts getting pretty warmed up in the 2 min. it takes for me to get from my driveway to the first intersection on a cold day, and gets so hot so fast I have to turn my heat down or off after 10 minutes.

Reading stuff like this...really makes me appreciate the things on my truck that DO work well. Also, Ford hates anything non-motorcraft. I still keep every single motorcraft part I take off just in case S hits the F and my truck throws a fit. Good luck!