ATX question

[94carolinaSHO]

Hello all,
I am a new member and new owner of a 94 SHO with 106k miles. Pretty much stock but kept up well. My question is while i am driving down the highway at lets say 60 mph, the rpm is at 2500. As soon as the temp gage needle gets to the bottom bracket, i dont know what to call it, the line between dead cold and the L in normal, the rpm will drop to 2000. It almost feels like it shifts into overdrive. I know that it isnt overdrive because to troubleshoot and see if overdrive works i have taken overdrive off and the rpm goes up to 3000. So i put it back quickly and it goes back to 2500. This morning was real cold and it took about the whole commute, approx. 1 hour, for the needle to get up to the ''bracket". Once it did the rpm went to 2k. However after having to slow down for some traffic it cooled down below the mark and went back to running at 2500 once traffic picked up speed again. Once at the mark it ''shifted'' back to 2k. I do have good heat in the car but this gage takes a long time to move. Does anybody know why the engine holds the rpm's up until it gets warm like this? Its aggravating because I am killing my gas mileage the whole commute until it gets warmed up. Plus i dont care to be running at 2500 for no reason. I love this car and would like to keep it around for quite some time but it has some quirks to it.
Thanks for the help and for the great website. I have found many answers already without having to fill up the board. But this one is interesting. Any help would be greatly appreciated.

 

[hawkeye18]

The dip in RPM is the torque converter in the tranny locking up. The torque converter (TC) won't lock up until the temperature of the tranny fluid reaches a certain point. Problem is, the tranny fluid runs through the radiator (which also cools engine coolant).

What is happening is that your thermostat is sticking open. This is an extremely common problem with SHOs due to their iron block/aluminum head construction. When this happens, the coolant is circulating through the radiator from the instant the engine turns on. Well, as I'm sure you know, it's f#%*ing cold outside. So, the coolant almost never heats up, because that thermostat really needs to be closed to keep the radiator out of the loop until the coolant warms up enough.

Now, since your coolant stays f#%*ing cold, it imparts this coldness to the tranny fluid, which is sharing space. And, since your tranny fluid never gets warm, your torque converter doesn't lock up.

I can guarantee you, if you replace your thermostat all of your problems will go away, and as a side benefit your mileage will increase, as the computer will just pour fuel into the engine while the coolant is cold to try to warm it up.

 

[94carolinaSHO]

thanks a lot. I was wondering if it had anything to do with the fluid and if it was connected somehow to the thermostat since it takes a bit for the gage to start moving? Do you know the stock temperature for the thermostat?
As a side note , how is advancement in the aviation field? Im a GSM2 and it sucks. I was think ing of cross rating to the same rate that deals with gas turbines as i do know. Thanks for the help.

 

[Rubix]

Do you know the stock temperature for the thermostat?

88C / 192F


-Jamie

 

[hawkeye18]

Normally they sell 185 degree and 195 degree variants. I would recommend the latter. It seems to be a consensus that the SHO engine likes running a little hotter.

If there is no "jiggle" valve at the top of the new thermostat, make sure you drill a wee little hole at the top of it to let the air bubbles get past. The stock Motorcraft unit ($$$) will more than likely have this valve, whereas Stant ($) t-stats probably won't.

 

[Troywakeling]

When I did mine I used the 180 degree one. I recommend changing the two coolant sensors while you do the T-Stat as well. Theres a small one forward of the Thermostat housing for the guage, its cheap only a couple bucks if I recall. The fat one is behind the Thermostat housing and it goes to the ECU, its like $15-$20. Saves having to buy coolant again if one of them fails and they are easy to do and right there.

 

[hawkeye18]

I think the front one is either a 17 or 19mm socket (deepwell), and I know that the rear coolant sensor requires a 1" deepwell socket. Don't forget the teflon tape!

 

[94carolinaSHO]

thanks very much for the info. I greatly appreciate the detailed information. What service manual do you guys use. My haynes that came with the car has no SHO info. What else is there available?

 

[94carolinaSHO]

one more thing. would it be wise to go ahead and do a radiator flush before hand? I did this however on my 5.0 and unfortunately wound up replacing the radiator due to some much crud coming out from water hardness from the previous owner. So im kind of hesitant and wondering what anyone else's outcomes have been and is it a good thing to do or not necessary?

 

[hawkeye18]

As long as the coolant that's in there hasn't been in there for years and years and years, a simple drain n' fill should suffice. There's a drain **** on the driver's side of the radiator at the bottom.

I haven't heard of too many horror stories coming from radiator flushes. I suppose if you're willing to go through the effort, then go for it.

I use the Factory manual. I got mine off of Ebay, you might try looking for one. They pop up every once in a while. It's the Taurus manual but has plenty of info for our SHOs.