Basic logic kicks in...you're right. Now I have to rethink the entire situation. Thanks for the thought Yoda

 

maybe the Tstat housing is messed up allowing "cool" coolant past the closed thermostat

 

put a blank in it to see if that would bring it up ofcourse you'll need too put a small hole in the center to prime up

 

I'm totally baffled. You say the upper radiator hose is not hot. The temperature gauge is reading only 1/4 of the way to hot. The heater blows cold air. This all tells me the coolant is "cool". Is the upper hose pressurized? (Not "squishy") when the engine is running?

All this "cold" stuff HAS to be an open thermostat. Maybe try a higher temp one? Do they make them that open at 205 degrees - I haven't looked for one in a long time. Was 195 correct for your truck? The normal operating temperature should be in the neighborhood of 205-215, I think (depending on engine load and outside temperature).

For my truck, the thermostat should start to open at 188-195 and should be fully open at 208-215. I don't recall if the temperature rating of a thermostat is the "start" to open temp or the "fully" open temp.

A cold heater COULD be a blocked coolant line into the heater core. Possibly a stuck valve. But, that doesn't explain your other symptoms.

All I'm really doing here is "thinking out loud". I've found this sometimes helps us to see other possibilities.

- Jack

 

Jack- this is when an infared (sp?) temp gun comes in handy. Also, a Scan Gauge, to see if it's ever going into closed loop. I believe experience can go a long way but I'm a firm believer in some basic, proper diagnostic tools. This is a case where you can chase your little hiney without them. It just isn't making sense. If the thermostats that have been installed are opening properly in test water at the rated temps.----
Jack- my truck is an '04 w/5.4 but i doubt that it would have a different temp thermostat than yours and on my Scan Gauge the temp runs a consistant 192-193 degrees, never above 195. The govt. controls the temp of that thermostat more than Ford does, through polution laws.

 

If it were me I would get a new thermostat from Ford and put it in. While your at the dealer pick up a new rad cap. When you install the thermostat you will have to drain some coolant out, which you know, make sure when you fill it back up you have the heater temp turned on to full hot and let it run with the cap off until the thermostat opens and burps all the air out. Top it up and put the cap on. Add extra coolent as it will suck it into the system when it cools down.

 

Hi Code. According to Haynes, which is the only "shop manual" I have (not much, I know), we both use the same thermostat.

Now that I think about it, I've never bothered to monitor the coolant temperature since my truck has a little dashboard gauge and it always shows just under halfway to hot. But, I DO monitor the CHT on my Gryphon and it tends to run in the 200-210 degree range. Since the coolant temp is not really measured in our engines, but only inferred from the CHT, I thought it was better to watch that. If I'm not towing, and not really demanding much out of the truck, the CHT stays at or slightly below 200. But on a hot day, climbing a hill and towing, I've seen it get to 214.

I will say, the engine in my truck seems to reach normal temperature more slowly than other vehicles I've driven.

I'm still mystified about Foe's truck though. The engine IS producing heat - lots of it! That heat has to be going somewhere and about the only place it CAN go is into the coolant. I agree with you that an infrared temp gun would be a nice thing for him to use to get an actual measurement. I've seen some that aren't too expensive.

- Jack

 

Put in a Ford OEM thermostat and now the problem is even worse. Engine is running super cold, taking over 10 miles to even to get off the cold mark on the gage. Upper hose is cold, heater blowing cold air and the upper hose is fully pressurized. Thermostat is installed correctly, including the bleed hole clocked at the 3:00 position.

After running 20 miles I can literally hold my hand on the intake manifold and heads. Didn't try the exhaust manifold ;-)

I am totally stumped.

 

What's the Temp on that thermostat? I just ordered a 190 this time. OEM is 195. You can get a 180. It's a b^tch getting the air bled from the block when flushing the system unless you fill a certain way. I found this out early on.

Not sure what engine and year you have, I'm not searching for it - You should fill in your info (top right corner of your post) so we can see. Some models have a temp sender (brass bulb) that gets cruded up, you have to wire wheel them once in awhile.

 

Thermostat is 195

Going to break down and take it to the dealer Monday. I believe there's air trapped in the system and I've been unable to bleed it. will let you know what they find out.

I hate going to a dealer not knowing exactly what needs to be done/replaced. Puts you at the mercy of the parts department....

 

Very easy to bleed - ALWAYS fill exspansion tank with top hose OFF thermostat housing. When coolant makes it's way to the thermostat, THEN connect hose and continue to fill to the line.

Then Start- warm up with heat cranked and with expansion tank cap removed - It's bled.

BTW - T-stat spring MUST be pointing toward the ground.

 

Foe Im gonna venture to say that your head gasket (warped head or bad gasket) is leaking slightly and pumping air into the cooling system. Once the engine is hot the leak seals it self (aluminum heads expanding enough to fix leak) and the system returns to normal operation once all the air is removed from the cooling system and ends up in the expansion tank.

 

Could be, the 5fours are notorious for leaking up front @ the water jackets. I personally never had a leak their, but I came close to it. My gaskets were deteriorating there when I changed them at 100k. At 186K, I changed thm again and my heads were pitted this time,- around the jackets. I had to fill/sand/polish. Now, I @ 256k and I just pulled the intake. - Nothing? Good shape..?? So idunno, but yea - watch that area for signs of leakage.

 

Almost for certain you would have the opposite effect. Exhaust gas is HOT and tends to super heat the coolant. The problem he's having is never being able to get the engine up to operating temp. It doesn't make sense, since the t/stat should guarantee that it gets to operating temp, especially with all of them that he has used. I still say I would get an infrared temp gun because that will tell you more than anything else will about what is going on with the "running cold" issue. I would even shoot the exhaust manifolds at each cylinder and compare with a like vehicle to see what kind of heat the cylinders are producing. I'm not sure even if it was running rich if it would be able to keep the temp. down that much. I mentioned the Scan Gauge and temp gun in my previous post because the SG would tell you if it was going into closed loop and the temp gun is an invaluable tool to diagnose unusual problems like this because it's able to isolate the problems (through accurate temp readings) that are tough to get the same handle on in any other way. I have a temp gun and use it frequently and consider it worth it's weight in gold. I think before he goes to Ford and throws a bunch of money at it I would definitely invest in one.

 

Didn't have some stray electrolysis going on there that you inadvertently corrected in the course of working on it that time did you Brew? No wonder that thing is doing so well at 256K Brew, it never gets lonely for your touch. I can just see you on a Sat. afternoon- hey, I'm kinda bored, i think I'll go pull that truck a mine apart just for the fun of it. You are a much valued part of this forum and I for one appreciate all of the priceless help you offer for no more pay than the satisfaction of knowing you were able to help a fellow traveler in time of need.