I'm going to flush the cooling system and replace coolant so was wondering if I need to replace the t-stat while at it. I'm suspecting it to be faulty as it takes a long time for the motor to warm up.
At about 65* outside it took exactly 12 min of idling for temp gauge needle just go past the first thick mark on the gauge. After 30 min of idling the needle just went past the left thin mark of "normal".
The top of the radiator is hot to touch, upper hose is probably as hot at the rear bend but it feels different touching metal and rubber so I am not sure.
What would you guys suggest?

 

Pull it, take a look. If you replace it, go with a genuine Motorcraft thermostat. The aftermarket ones are cheaply made and break very quickly.

Note that the engine doesn't make a ton of heat while idling(not like a gasser); it should warm up a lot faster if you drive around.

 

sounds like normal warmup times ..

even in the summer i start and let it warm up 10 minutes before i go ..

just because it saves fuel .. she drinks a lot more fuel when cold ..

but yea it will warm up to normal while driving .. they're cool idlers

 

Okay, thanks guys.
Since I want to flush the cooling system I was going to remove t-stat any way. Will then replace with the new one just in case. Hate to do a job twice.

 

Service manual says "never remove thermostat". I heard some people do.
What's the deal with this?

 

I've never heard that one before It's a pain to get at, but just remove it, inspect it, and replace if you need to. Although, your warm up times are pretty normal so I would bet your T stat is fine. It doesn't hurt anything to pull it and replace it if you just want piece of mind

 

if i leave my 88 sit, it will take close to 45 minutes to make heat enough to warm the cab. but if i fire it up, let it run for a minute or so them drive slowly down the road, it will have noticeable heat within 2 miles.

 

Same here. As soon as the high idle kicks down I just baby it down the road till she's in the normal range

 

Since Jarkill mentioned high idle I will ask a question which is off topic if you don't mind.
Mine idles at about 800 rpm if I can trust the gauge. For as long as I let it run.
Is there something wrong?
Problem is that I didn't get her on a road yet and the longest distance I drove it was around the farm when I went to buy her. Then she came on flatbed to my place. After driving about 200 feet back and forth on my driveway I don't see any change in idling speed even when it warmed up once to what I think would be a normal operating temp.

 

The fast idle solenoid can't actually 'raise' the idle speed any, its not strong enough to counteract the return spring. However, if you pump the accelerator to override the return spring, the fast idle solenoid will then be able to hold the idle speed higher. Thats why the starting instructions mention hitting the pedal before cranking.

Pull the thermostat and check its operation by dropping it in a pot with a thermometer and watch it as you bring the water up to a boil. Note the temperature at which it starts to open and is fully open.

As noted, if you opt to replace it, do so ONLY with a Motorcraft thermostat as noted above. Aftermarket ones do NOT work properly. Rockauto or Amazon should have a good price on them if local sources don't carry Motorcraft ones.

Even if its snowing year round, you're wasting MORE fuel letting it idle for 10 minutes instead of just driving it. If you're concerned about the small differences in fuel when cold versus warm, use the block heater to prewarm the block. Like Tom said, idling doesn't warm these babies up, they need to be driven to get there. Once you have oil pressure, go ahead and drive it.

 

Yes, I know there are a few parts which you don't want anything but Motorcraft or International.

Where the fast idle solenoid is located? If that's the one behind the bracket on the accelerator cable there is a gap like 1/16". Hitting accelerator before cranking means hit it all the way and release or hold it? Is the same true for both manual and E4OD?
Was trying to get a user manual supplement for diesel but couldn't find. Those are available on Ford's web site but only starting from '96.

I guess I'll need to start a new thread on this later after I'm done with coolant, belt, tensioner and idler.

 

I can't remember exactly how its stated... but goes something like this:
Turn key on
Pedal to floor and release (in cold weather hold pedal halfway**)
When wait to start like goes out, crank engine

It may state hold pedal halfway all the time, and fully down in cold weather... Basically the tap to floor lets the fast idle solenoid extend. Not sure if it was in all trucks, or if a PO removed it, but that info (and more!) is on the driver-side sunvisor on a sticker. And yes its the same for any transmission.

 

On mine you just push the pedal a quarter inch and you'll feel a click, then fire it up.
I usually start the truck before doing that and let the oil pressure come up, then I set the fast idle after it has run for 20 seconds or so.

 

Here you go. I happen to have the book in question.

 

Warm up info..