Hi,

1998 Ford Econoline 106,000 miles 5.4l.

I noticed the truck was taking forever to warm up and never reached an acceptable operating temperature. I was positive the tstat was stuck open. Replaced the tstat yesterday and come to find out there was no tstat installed. Thought bingo! Finally the truck will reach operating temperature, I will have heat, and everything will be dandy.

Replaced tstat with ford part
Genuine Ford Thermostat 7L3Z-8575-D

Also used a rubber gasket got from local auto parts store that didn't fit around the tstat. install went tstat in the housing, rubber gasket on top, then the top tstat housing cover. It kinda sat up like a 1/2" high due to the seal, but it sucked down the bolts. We had watched youtube videos and this seemed to be normal. My thinking now is that maybe the t-stat isn't sealing properly and enough water is able to get around it. However I kinda doubt that at the same time.

Anyways replaced tstat. Added coolant flush and distilled water. Ran truck for 20 min at high idle and temps never reached above 160-170 at upper radiator hose. Heater never blew warm air really at all.

We are now thinking the fan clutch is bad causing the fan to be pulling too much air at idle / lock up too quick. Is that logical? Is there a good test for this? Anyone have experience with 5.4l not getting up to 190-200 temp?

 

I also did drill a tiny bit larger hole in the dangle that is on the tstat. Which is something I have always done in all my cars and never had an issue. It is seriously a small hole, don't really think it could be causing too much water to be bypassing tstat causing it to never run hot.

 

I'd bet you have at least 2 problems and one of them could be the gauge. Are both heater core hoses getting warm? If only 1 is that suggests a clogged heater core, flushing that with a garden hose will often clear it out.
Next is to figure out if the motor is actually getting to full operating temp, for that you need something else to measure water temp like an infrared tester or another hardware based temp sensor.
If you can rotate the fan by hand when it is cold the clutch is OK, it should not really spin but it should move smoothly and without needing a lot of force.

 

1. If heater core was clogged that wouldn't contribute to it taking forever to heat up? If anything it should heat up quicker correct? Also, we are reading temperature using an IR gun and getting hottest temps of like 160-165.

2. lower radiator hose feels noticeably cooler than the upper one.

 

also yes at cold there is some resistance moving the fan, but not much. as soon as you start the truck up at cold it is blowing quite a lot of air over the radiator.

 

It won't make much difference either way.

OK that is good info.

Have you driven it? An idling engine won't heat up very quickly especially in colder weather. Does the truck have a single or double core rad?

 

Yes. And also an engine should warm up by itself holding a high idle or even just idling. It definitely is taking too long / never reaching a real operating temp. Anyone else have any other ideas? Could the fan clutch be bad making the fan push too much air at idle? Could the thermostat be faulty and be opening too early? or the O-ring isn't right and enough water is able to get past the thermostat?

 

I have a bad feeling about your description of the o ring/gasket for the new thermostat. I’d go there first.

 

I have a suspicion your blender door motor is bad and is not set for heat, if I solely went by the gauge in my E350 I'd be blocking off the radiator, BTW my stock radiator split open, I don't know how long I drove this way, it never ran hot, I just found it when I noticed the low tank and tried to fill it. FYI a fan clutch does not fail in the terms of locking to on all time, the fluid leaks out and it fails to fully engage, I replaced this too when I replaced the radiator as it was weak. I bought a 2 row welded aluminum radiator far superior to what was in my van to start with, then another clutch for the fan, there is absolutely no difference in the temp on the gauge or my heat. Several years ago I found my blender door had failed because it was summer, yet the dash acted as tho it was winter, smothering me with heat, drove around with the rear air till I replaced the blender door motor, just prayed it was the motor, not the arm broken from it.
If you are adamant you are running too cool my suggestion would be, replace the thermostat and DO NOT drill a hole in it.

 

make sure you installed the thermostat the proper direction or it will be sensing the hose coolant temp instead of the engine temp. you can test any thermostat by placing it in a pan of water on the stove and using a meat thermometer like you would use on a turkey to see what temp it opens at and how far it opens. you can get a bad thermostat right out of the box seen it many times.

 

I took mine out today, it's finally gotten cold outside, after starting it, within a few minutes, even before the gauge has moved 1/8" the heater is blowing warm.

 

Ok, your engine isn't reaching operating temps, if I'm understanding this.

#1 go get the proper T-Stat and gasket, don't mickey mouse it.
#2 are you staying at a higher idle because of the cooler temps on the engine? If you are...

#3 it could possibly the ECT or the connector for the ECT, it's under the T-Stat housing.

#4 there is a possibility it could also be the CHT.

#5Before all else, I would put an OBD scanner on it and see if any codes are being thrown...Not all codes will turn the engine light on, so it's always good to do a scan before all else.

 

Ok here is the update:


Heater core was plugged completely.

Replaced heater core and everything works great.


My FINDINGS:

1. Bottom radiator hose at operating temp won't feel hot.

2. Normal operating temp on guage dash isn't very high definitely bellow middle

3. If your heater core is clogged you can tell by if you put ur hand on the black heater core box under the passenger side glove box area then you won't feel any warmth. When heater core is working itll feel hot on the black box. You can feel if blender door is working by putting hand behind and moving temp gauge and you will feel door moving.

4. thats all ! thanks to everyone.

 

Yeah, the 5.4 doesn't run hot like you were looking for, I knew it was at operating temp, how hard is it to replace the heater core?

 

Not hard.

Here are my tips:


Use sharp razor blade to cut both inlet and outlet hoses right at the quick connect on the heater core.

Use dremel or dykes or something to pull off the quick connect plastic / break it / get them off.

Remove 8mm bolts under dash area that hold black hood that covers heater core. Melt the area around the philips head screw that is super difficult to get too using a knife heated by a torch some prying and don't be shy.

Once you get that black cover off pull heater core off.

Replace with new and use hose clamps standard. you can tighten them with a 1/4" ratchet.