BTW, I don't know which tstat I put in it. Whatever the napa guy gave me.

 

I see the t-stat and i see the port at the bottom. Can you explain more how the port gets blocked by the t-stat when it opens? The t-stat disc just moves up and down on the shaft.. I think that bypass port is always open and the coolant flow will take least resistance.
When mine failed, I took it out in a mcdonalds parking lot. Motor ran nice and cold while it was out. Maybe a 1/4 up on the gauge 140 degrees maybe..

 

I thought the disc only moved up and down on the shaft as well until I tested it in boiling water. It moves up and down on the shaft yes, BUT the shaft itself moves down when the T-Stat opens up. From what I saw in the test, the bottom spring on the disc is there to apply pressure on the disc, not to make it move. When the T-Stat opens, it pushes the shaft/disc down and closes off the bypass. The bypass should be fully closed, or close to it, when the T-Stat is fully open. That is why these trucks use the long version T-Stat and not the short one.

As you can see in the picture, the disc is on the bottom with the bottom spring. The upper spring and upper disc is what shuts off the flow to the radiator. The upper disc and the whole shaft is what moves down. I thought the upper disc just moved down on the shaft but it is the whole shaft that moves down.

Note: RiffRaff Stock unit on the left, DieselSite *203 unit on the right.



It is a good idea to always test a new T-Stat before you put it in. I got a bad *203 unit that would only open about 1/8th of an inch at the most. Testing it and the stock unit side by side showed there was a huge difference.

 

Just an update and a question. I replaced the t-stat with no improvement. It is the long t-stat. I also tested the old one and it was opening fully. After reading everything I can find on this site, I'm convinced now that the radiator is the issue. My question is will a 99.5 radiator fit my e99 as a straight bolt in? If so, will go that route and take advantage of the built in trans cooler. I appreciate any thoughts.

 

Yes a Late99- 03 radiator is the same size as our Early99 and has the trans cooler built in. And I think think even if you weren't having problems it would be a good upgrade for any E99.
http://www.rockauto.com/catalog/moreinfo.php?pk=3610128

 

Well at least it was cheap to try a new T-stat. I cant answer your question about using a e99 radiator but I dont see why it won't work.

Edit: I meant L99

 

hey puff, the radiator may bolt in, but I have a 99.5 and it doesn't have a cooler in it.
I put in a 6.0 cooler. might check that.

 

Your radiator doesn't have the trans cooler built in it ? When I looked up the Radiator I used 2000 model year. Sorry I guess I was wrong about Late99.

 

Roger that guys. I'm heading to the part store and see if they can get close to Rockauto on price. If not, shipping doesn't look to bad. Thanks for the feed back

 

I would verify the degas tank cap is holding pressure before replacing anything else. When the cap fails, these trucks will run cool all day long (even in the summertime with A/C blasting) but then overheat when towing heavy.

I have experienced some issues with Ford replacement caps not sealing well on the tank threads so you want to be mindful when replacing caps. I think I have a photo somewhere....

Found it. (see attached) The cap on the left is a Ford replacement part but it did not fit my '99 bottle very well. I screwed on but didn't hold pressure because the plastic threads didn't grab well enough. The cap on the right is also a Ford part. PaysonPSD found this at his local dealer and it worked perfectly for me. Once I got the black cap installed, my over heating problems vanished. Just an FYI...

Good luck!

 

That's good to know Greg. I never thought of the cap might be the problem.

 

From what I've seen, most 1999 models (early or late) do not have the OTW cooler in the radiator. It's recommended that folks with 1999 models upgrade to a 2000 or later when replacing their radiators.

 

The cap seems fine and I don't loose coolant. Is there a way to pressure test it? I've already ordered the radiator and it sounds like its good to upgrade. Would I leave the air trans cooler in series and if so, before or after the water cooler?

 

On my 2000 model year trucks...
The fluid line at the forward part of the transmission runs directly to the radiator fitting. The hoses on that line are crimped...I suppose because the pressure is a bit higher at that point. The line that exits the radiator runs to the oil to air cooler buried behind the AC condenser and then returns to the rear port of the transmission.

I had a diagram somewhere but I can't put my finger on it right now. Sorry.

 

That's good info Shake, I'll hook it up that way when i get it installed. I'll post back and let everyone know if the radiator fixes my problem. Don