It's time to change the thermostat on my '99 F. The picture is the temp guage with a fully warmed engine at 30 degrees air temp.

My Chiltons manual says to disconnect the negative battery cable. I have no problem doing this, I just wondering why? Does the PCM store temp information that may be affected after changing the th?
Who has not disconnected the battery?

Also, are there any major differences in thermostat brands? Any to avoid?

Thanks, FL

 

just change it and dont worry about the battery cable unless the alternator has to be removed to get to it. buy at any good parts store, not autocrap

flush radiator by removing plastic plug on bottom

 

just make sure to test the new thermostat before you install it. Stick it in a pan of water over the stove, heat water till almost boiling and watch it open.

Every now and then you get a defective one brand new no matter what brand you get. I'd say brand doesn't matter as long as you test.

 

Good suggestions from these guys, flush and replace. One thing to add is change the clamps to tridon screw on clamps at all ends. Easier to remove later. Also, stat brand is not really an issue as long as it works and is the right temp, stock bieng 192 or so.

 

You are almost always encouraged to disconnect the battery when doing anything under the hood to lessen the chance of accidentally grounding a live circuit.

As far as t-stats go, avoid Stant. They are notorious for being off, brand new. In my experience, Robertshaw t-stats have the best record for being accurate right off the shelf. That's what I usually install in my customers cars.

 

Hmm... Seems odd for a thermostat to quit working on a relatively new truck with only 40,000 miles on it....

Just thinking.......

 

It's 7 years old now. Plus I'd bet a dollar that it had 40K miles on it when he registered for this here site in 2003.

 

Yeah.. I guess.....

 

Thanks for the info.

I've been looking all over for for a Robertshaw thermostat without luck. I finally found a phone number and discovered that Cooper Standard bought out Robertshaw thermostats several years ago.
Cooper Standard makes Prestone thermostats. They make three models, OEM replacement, Gen 2 (lifetime warantee), and Extra Performance. I'll probably go with a Gen 2 if I can find it.

http://www.cooperstandard.com/us/en/...Thermostat.asp

 

I agree, the whole disconnect the battery thing is the first thing 'they' say to do for any procedure..... Just a liability thing I'm sure.... Just like the 'warnings' you see about the fan (don't put your hand in the fan while it's running..) or don't use a match to check for gas leaks.....

I could not find an aftermarket T'stat for the 5.4 at the local parts stores... I just went with a Ford part and it had the new O ring and everything. Can't remember the price, but it was not something I even considered anyway... I just want one that fits and will work!

You should consider replacing the hoses too.... That lower one is a spendy one ($70.00), but compared to the 8 year old one that came off, I was glad I changed it!

Mitch

 

That's good to know. I used to buy them in bulk from a local supplier before they were bought out by Napa sometime in the past year or so, but there is also a company called Stewart Components that has hi-flow Robertshaw t-stats. They're the ones that most of my Mustang customers get.