Erratic Temperature Sensor Readings

[FR-425]

 

[teletekman]

Ok, well another temp gauge did the same thing. Took out the existing sending unit completely and installed the new sending unit that came with the gauge so nothing was related to the existing setup.

Watched my scanner monitoring the ECT sensor and the readings were inline with the gauge. Varied from about 185 to about 208 or so at idle and warmed up.

One thing I noticed was at the higher RPM's (2000) the gauge would fluctuate about 195 to 215. Assuming this is because of the greater flow from the pump? This was also monitored at my scanner as well. So I think at this point the existing gauge is ok.

Could it be as you mentioned before that there's still a nasty air pocket somewhere that no matter what I do it just won't give itself up? I have purged and burped and purged and burped and purged and there just isn't any difference in the temp gauge. I have tried every method I can think of that I know and have read about. Are these Explorer cooling systems that stubborn?

I did order one of those Snapon Air Purging systems on fleabay yesterday for a kick ass deal so as a last resort I can maybe put the system under vacuum and try it that way. After literately doing this countless times I have to say this is a first for me....

 

[FR-425]

Jeeewhizz huh?

I've heard the 91's and 2's are alittle more tricky but not like that.

 

[FR-425]

Dang,

I'm thinking now that your radiator is just beyond plugged up.

To the point that it's replacement time.

The water passages in the engine are not small enough to plug up to the point that a flush won't get it, But a radiator can.

As you flush, the water just bypasses the stopped up portion of the rad.

I'll bet if you knock one of the tanks of the rad and have a look; the bottom half is solid plugged.

 

[teletekman]

I forgot to mention that the radiator was replaced about a year and half ago. Ill take that radiator out and down to the shop this week and have it looked at.

Another question, if i did have a water jacket or two plugged up somwhere on the block, would i be seeing the temp fluctuation im seeing now? Or would this be something thst would get to the point of it boiling over? I can figure out why with the cap off temps stabilize but with it on thats when everything goes haywire...

 

[teletekman]

Also when i flushed it out the last time, i took the radiator out and ran a water nozzle full blast on the top and let it push out the bottom. I didnt notice any crap coming out and flow looked decent...

 

[FR-425]

This is just bizarre!

Are you running water only?

 

[FR-425]

Ok I know how this sounds, but here goes;

Disconnect your heater hoses and bypass the heater control valve.
(so that your heater hoses run from water pump back to water pump)

Just use a piece of 5/8 tubing of any sort and a couple band clamps.

Eliminate the valve as the source of air in the system. (the heater control valve is at the highest point in the system (flaw).

Replacing the valve has been the solution to this. But best to test before you go spend'n more hard earned $$$$

The stupid little ball in the valve breaks off the shaft causing erratic heat in the cab and funny business with air in the system. Rare these days because most have already been replaced long ago. The new design is the fix.

Forgot about this little diddy! Major PITA to go through all the rigamaroll for this kind of glitch.

 

[teletekman]

No i'm running 50/50.

I'll try bypassing the heater core. I was wondering about that the other day as well.

We are getting some heavy rain over the next few days so it might be a bit till I get to moving the heater hoses around unless I get a break in the weather.

I'll keep you posted as soon as I do. Thanks for sticking by with me on this.

 

[teletekman]

I was thinking back a while when my dad first gave me this Ex, I replaced the intake gasket and had to refill and burp the system then but did not have near the headache that I am having right now.

I am wondering now if maybe there is a blockage somewhere or all of the sudden I do have that nasty air bubble that's getting free rent in my engine?

If I did have a blockage or even air escaping wouldn't that send the temps up and pretty much stay there? There is no leak dripping or boiling over anywhere that I can see...

 

[FR-425]

Just depends on exactly where the blockage is.

Still need to do the bypass to be sure.

This is the kind of thing you see on a custom build that has to small a radiator; the temp jump'n around at idle, and then when driven it just over heats, that's why I was thinking plugged up rad, which is still a possibility.

 

[teletekman]

Ok, decided to do the bypass last night before the rain hit and made some progress! So as you stated, I bypassed it at the heater core and afterwards let it burp a bit more. Temperature did stabilize right between the O & R markings. Decided to take it for a test drive and for the most part stabilized right at the same spot or right under the R mark. So far so good!

Now I did notice that while it's stable, when ever I rev the engine up or accelerate for that matter, the gauge will start to drop right about the N mark and eventually will start to make its way back up to the R mark. Sometimes falling short but now it won't go passed it.

So I think you got me on the right track here. Assuming that without the heater core in the equation could the current needle swing I have still be attributed to air still inside?

I am running a Motorcraft RS-90 16lb cap and after one of the runs last night I did look inside the over flow resevoir and can see a little bit of air still coming through. Originally I had an aftermarket 13lb cap and never had a problem with it although it did fail a recent pressure test. Do you think dropping back to a 13lb cap will allow any trapped air to bleed out to the overflow resevoir? I am wondering now if any air is that is still trapped inside is having a hell of a time getting passed that 16lb cap?

 

[FR-425]

Ah ha,

Now were getting to the bottom of it.

Yes get the 13psi back on there or your overflow bottle will always be dry.

So, all this and your heater control valve is the bad guy. Replace and be happy!

You must still have the defective design on your truck. It is the valve that is the prob not the heater core. Although a clogged up heater core will attribute to fluctuating temp in the cab.

The temp drop on initial acceleration is the fan running. The fan clutch will run when cold and also come on after coming to a stop for just a short time. Weird I know, but normal. The clutch triggers at idle not so much because the engine is hot but because the there is no forced air flow and the clutch itself is hot. They also have a lot of drag when the oil inside is cold. So it can be a little confusing in cold weather. Make sense?

So, yes; That small temp swing is normal cycling of the thermostat and the fan clutch

 

[teletekman]

Well our recent rain came and went so today was able to spend a little more time on the Ex today. I took it for another test drive today and here again is what I noticed...

Sitting idle in the driveway for an extended period of time the gauge will now eventually make its way to the middle mark. So far so good. While revving it up noticed the gauge start to fall fast about to the N mark. After letting off, the gauge would start to creep back up. Sometimes it would make it to the middle point, sometimes it would sit at the O mark. Still no major fluctuation like I saw before. Again so far so good.

I looked around and I guess my design does not have a heater control valve. The heater hoses go straight into the heater core. So pressure blasted the hell out of the heater core and seemed to have good flow. Also put it under a vacuum for about an hour and it held great at 20 inch pounds with no drop. So ended up replacing the heater hoses and getting everything back together. Let the system burp again and took it for another drive.

While driving down the freeway, gauge would get to the middle mark and stay there. If I revved it up it would drop and then make it's way back. At one point it did creep up past the middle mark but only once and then it settled down. Driving through town, it would never quite get to the middle mark but I did see a little bit of fluctuation depending on if I was accelerating or not. Eventually it would settle at some point but never past the middle mark.

So I think I have come quite a ways from day one of this issue with your help. I understand that accelerating will affect the flow quite a bit but I just don't remember the gauge doing that before. I have pretty much replaced the entire cooling system's components all with OEM parts so everything should be working.

So does this still sound like it's operating like it should? I understand that my mechanical fan clutch can play a great deal in this since it's Fords heavy duty clutch. Just haven't heard of anyone else mention this kind of swing before even under normal conditions...

 

[FR-425]

Yeah, that sounds completely normal.

When the weather warms up it will run a bit hotter (obviously) but it will fluctuate less.

Just the cold weather and a NOW normal cooling system.

Must get hot in the cab in summer with no way to shut off the heater core. ! ?

Glad to be of help.

 

[teletekman]

Well just wanted to give you an update after driving it for a couple hundred miles since my last update. The needle has sitting idle around the "O" mark after reaching operating temp which has been a major improvement from before. So my radiator cooling filler kit came in from fleaBay and was in pretty good condition for the $40 I paid for it. Anyways, I drained the coolant once more tonight and stuck the filler on. Drew a vacuum and it held great for a few minutes with zero bleed off. Let it refill the system afterwards and did exactly that with no problem! Took it for another 45 mile drive tonight and low and behold, the needle crept up and stayed exactly in the middle the whole time! So I guess I might have had that minor little stubborn air bubble still in the system but this kit fixed that right up!

I see what you mean now and yeah I guess that would make sense when you accelerate it flows quicker and pushes that cooler coolant threw the system causing the gauge to cool off but then eventually makes it way back to the middle. I am thinking of going the electric fan route since I can feel the drag of the mechanical fan clutch which I have also some questions posted in the modified forum but I'll save the rest for that conversation.

Anyways, just wanted to extend a heartfelt thanks once more for stickin with me through my little dilemma. Very much appreciated! *cheers*


Sean

 

[FR-425]

Fill Kit?

 

[teletekman]

Yes sir. Picked up one of these just in a black case...

Worth every penny IMO...

 

[FR-425]

Ok, looks interesting. Sort of a pressure tester with a bleed valve. Nice