Hey all, I'm new to the forums. I've had Fords all of my life and it's actually my dad's truck that I'm asking advice about, but I've changed the three thermostats that we've tried in it so far, but the same thing. I've also changed the front left fender because it was rusting really badly in the usual place right at the door on the bottom, but this truck has the 5.0L 302 and other than a timing chain when we bought her almost 11 years ago, she runs strong at 214,500 miles on her.

Anyway, we have been having a problem lately where the temp gauge stays right on the N where it says 'Normal' on the gauge and while under acceleration, the needle will move up to the middle of the gauge while the accelerator is down, however when you let off it, then the needles drops down to or below the N. So I thought thermostat, so the first time I switched it, I went and gotten a premium Motorcraft thermostat and put that in. For a month or two it worked, but then it started doing the same thing. SO I went to see if the standard replacement off-brand thermostat worked and it did for about a day, but then the truck did its dirty old tricks and wasn't warming up, and the heat in the cab was coming out luke warm when before the thermostat problem, on a subzero day, you turned the heat on half speed and in no time it would roast you out. Long story short, this truck keeps going through thermostats.

One thing I was actually thinking about trying was a Mr. Gasket high performance 195 degree thermostat, but I don't think that will do anything. Just wondering if anyone had any input on this?

 

At first I was thinking it could be the sensor/sending unit but then you said that it doesn't warm up as quick. I was told that most temp gauges are averaged so they don't show spikes, like my Monte Carlo sits in the middle all the time but my 944 will go to the top of the gauge and then you can see when the thermostat opens and it starts dropping again.

None of that is really useful as I don't know what these pickups are supposed to do, mine only moves a needle width weather it's up to temp or not.

What do the old thermostats look like? It sounds like they're getting stuck open, is there something that's getting stuck in them? Gunk in the coolant or maybe just old gummy coolant?

 

The old thermostats look like any other thermostats.

This is the Motorcraft one I put in first. It's a 195 degree standard thermostat:


The standard off-brand one I put in after the Motorcraft one was practically the same exact thing. They were identical.

Off-topic, but here's a picture of the truck. She is a 2wd and when you look at it from different angles, it looks like a heavy half-ton, but then other angles, she looks like a little truck. But still, wearing a flannel, plaid button-up shirt, my camo hat, jeans and my work boots, the ladies turn their heads when you drive past. Haha.

When my dad and I picked it up from the dealer, we went and cleaned it out completely, vacuumed it out fully and so the inside was completely spotless, smelled good, and then we pressure washed outside, and the whole undercarriage, because it was late February/beginning of March to clean all the salt from the roads off it, and back then, she was rust-free and a gorgeous truck. But when we towel-dried it, and put two or three coats of turtle wax, and two coats of carnauba wax, shined the wheels and scrubbed and brushed the running boards, going down the road, she glitzed and sparkled off all the buildings and people who saw it, watched it in awe and we got so many compliments for how clean and nice we kept it. But now it has the inevitable rust on the top of the wheel wells of the bed, and currently has no rust on the front fenders but the right side was run into while I was driving it through my school parking lot at the end of the day. With a bit of haggling with the person-who-hit-me's insurance company, we got to drive a rental, BRAND SPANKING NEW, 2012 F150 XLT crew cab for a week and a half while the big blue was in the hospital getting fixed.

This truck has a lot of sentimental value to me because it was the first vehicle I drove(legally...shhhh) and the first vehicle I undertook a major repair "project" on my own and that was replacing the timing chain when I was 14. It was a rush when I started it up after putting the engine and everything else back together and she purred like a kitten.

Anyway, sorry for rambling. I stand to Ford trucks like I stand to breathing. The only trucks I will trust with any kind of work.

 

I apologize for the double post, but I haven't been on a forum before.

Now that I think about it, I can't remember when we actually flushed the coolant out completely in the truck...or if we ever have. Also, now that I'm thinking more about it, it makes sense that old antifreeze could stick the thermostat open. But then again, why would the temp fluctuate when the truck is under acceleration...? That is starting to make me think there's a pressure problem somewhere in the cooling system, because under acceleration, the coolant is running a little faster through the hoses/engine, thus giving more force to shut the thermostat.

Just my thinking at least.

 

Sorry, I should have been more clear. How did the actual used thermostat look after you took it out? Was it still clean and look to be in good shape? Nothing broken or caught in the spring.

Again, I don't know if the gauges read actual temperature or if they are more averaged out. However, the signal is an electrical one so it could be anything from just a bad sensor to voltage jumping from another wire to air in your cooling system.

Pressure shouldn't matter, thermostats open/closed based on metal expansion with temperature. Like this: If you're concerned about pressure then a flush might be in order next time it's nice out.

 

It doesn't sound as if the stat is your problem. You mentioned lack of heat coming out of the heater. You could quite possibly have a bad heater core. It's unlikely to have several new stats be bad. Start it up and check the top radiator hose. When the stat opens it should be pressurized and feel hot. It won't before the stat opens. If the stat were stuck closed your engine would overheat. If it were stuck open it would take longer to warm up, but it eventually would. I don't like the do it yourself flush products available they seem to just break crud loose that gets stuck somewhere else. It would be good to drain the system and put new coolant in since you don't remember when it was done(maybe while changing the heater core) as for the temp gauge you may need a new sending unit they're cheap and easy to change. Rememember to always be careful anytime working underwood with the engine running, like when checking the top hose

 

The gauge looked like new when I took it out. I was hesitant on whether or not to put the new one in or just put the old one back in, but I figured I'd try the new one, but to no avail.

On the heating issue, the truck used to just roast you when it was down into the negatives the past couple winters. The defroster also worked perfectly and now when you have it running at full blast and high temperature, it just spits out luke warm air, and the truck's temp gauge is sitting right at cold. It takes the thermostat, no matter which one it was whether it was new or the old one, takes them the longest time to open up, so while at an idle, it just idles in the cold cycle.

 

So it sounds as if the gauge is reflecting what is actually happening with coolant temperatures. It just doesn't seem right that you'd have multiple bad stats. Do you have a clutch fan? If its engaged all the time it will slow down the warmup process. I still wouldn't count out a heater core issue for your heater issue it's about the right age to be in need of replacement. If an engine runs its going to make heat. The fan and t stat help control how much and how fast. If then core is plugged up you can't get heat. As for the gauge it may or may not be accurate the only way to know for sure is an actual temp gauge not the sweep type like our trucks have

 

I meant the stat in my previous post. And it's not actually the heater, but the defroster, which I'm guessing that runs through the same thing, so it still could be a heater core. However I was helping change balljoints on my buddies 95 F250 HD with the Sno-fighter package, and a 351 in it, and he told me that his truck runs at the same temp where my gauge is, which looking at a 92-96 dash cluster, where it says "Normal", the needle sits between the N and the O on the gauge.

 

That's what I'm getting at. If the stat was stuck shut you'd overheat if stuck open it's slower to warm up, but it will still warm up. All the air in the heating system (heat or defrost) gets its heat by extracting heat from the engine by circulating through the heater core. It's probably like $45 and takes very little time and effort to change

 

It's definitely not the heater core. It was almost 40 today and forgot turn the heater off and I was sweating by the time I got to school. Heater works really well when it's warmer out, but really cold, it heats just nicely but same yjong happens as what I just explained.

 

Hey guys, I checked the heater core out and it was working just fine. The spring in the heater blend door, however, is stuck on heat and won't move, so I'm still trying to figure out how to get to that. I'm thinking I'ma have to tear the dash apart to get to it. At least that's what I'm thinking as well.

However, it's weird. It seems to throw temper tantrums and when I shut it off after driving it for a while, (heater only worked up enough heat to pleasantly warm the cab where if you were driving for a long time, you could slip your jacket off and not freeze, where if it were above freezing outside, it would just roast you like a thanksgiving turkey). But back to its "tantrum" I shut it off after driving around town and when I get out I hear a sound like liquid spattering on the ground and here, the radiator cap was spitting out coolant. Hasn't done this before, and so I'm thinking a new radiator cap would at least help if not fix the problem. Maybe it's something that small? I'm not sure.

And also, I want to sincerely thank you guys who have been giving me your input. I re-read all of my replies and it seems like I've just been shooting your inputs down, and I don't mean to come off as a D-bag. Just thinking intensely and all. But thank you, again, for the input and ideas. I really appreciate it.