Why is the coolant gauge always perfectly in the center on my ‘99? Is It a dummy gauge?

[JoshT]

all good points, but I work my truck hard. It could be 100 degrees pulling 3500 pounds up a steep hill in first gear and that stupid little water temp guage sits happily in the center. I really don’t care what it reads when I’m driving it to town for work, but when I’m hauling mowers I’d like to know if I’m working it too hard. Maybe the coolant system is way overbuilt and it’s just that good at keeping it cool. I really don’t know.

I was reading somewhere about the sender, and I recall hearing something about the resistance curve having a flat line or something where the operating range is. In other words, after it reaches operating temp it keeps voltage to the guage the same during a large range of temps. Once it exceeds that it’ll boost the current. I don’t completely understand this, but if it’s true then I should be able to get a different sender that’s got a curved line. I keep imagining it like a torque curve and how they are different for semi trucks vs city buses.

For future reference, anyone here who builds a vehicle or starts a company that does, I like to see real data in real time. Don’t care if it’s a little Honda fit or an F450, I like real information. Just in case anyone here begins manufacturing vehicles. That goes for you too Ford.

1) 3500lbs in 1st gear really isn't working the engine that hard. Trans, maybe. Brakes on the way back down, definitely. Engine, not really

2) The senders in these aren't that smart. The senders in most vehicles aren't that smart. Where that trickery comes into play is the computer, particularly in vehicles where the cluster is fed by the ecu I stead of directly. I'm pretty certain that in 98 they had a fairly dumb sensor that is connected directly to the gauge.

3) You and about 4 other people out of 100 (I'm being generous) want that type of real time data. The other 95 would be scared and confused by all that data. It would lead to a huge influx of people worrying over one instant issues. That means more customer complaints and worry work over things that don't matter, aka more expense to manufacturer. Manufacturers are going to aim for the masses and increasing profit. For everyone else the aftermarket has aux gauges, scan tools, and scan gauges.

 

[I support common sense]

Good question. I plan on adding one during my v8 swap and my plan, so far, is to put it in the outlet from transmission to cooler. Since my application is 4x4, I don't want it mounted too low where it could easily be damaged.

By any chance do you know if the outlet for the automatic transmission cooler is flared or pipe thread? I’m thinking I’ll put a T-fitting there and connect my cooler line and temp probe there. And maybe you happen to know the exact thread and what T-fitting I should get.

 

[Curious Hound]

I need a chance to go look at my transmission to refresh my mind.

 

[scotts90ranger]

I believe it is flare or some type of O ring deal, I don't remember... but I do know it is low pressure since it's on the return side so if you it isn't super imperative that you get anything fancy...

 

[Curious Hound]

I need a chance to go look at my transmission to refresh my mind.

I don't know about the cooler itself. But on a 2002 4r70w, and probably many other transmissions, the hole is threaded to 1/4" parallel pipe threads (NOT NPT). There is an adapter fitting with male threads that fits into the threads on the transmission case and is machined to female flare fitting specs. Should be 3/8" flare fitting for 3/8" tubing. I have not finished Googling for a tee to fit that combination. It will probably require 2 or 3 fittings to get the right combination of male and female stuff. With it being low pressure, 1/4" NPT might seal ok in the parallel threads.

Upper hole empty female 1/4" parallel pipe threads. Lower hole has the adapter installed.

the adapter fitting, showing 1/4" male parallel pipe threads.

The female end - 3/8" tubing flare.

the flared ends of the hard lines

here, I threaded the adapter onto the tubing and flare nut.

 

[I support common sense]

That’s awesome thank you. Now correct me if I’m wrong. Wouldn’t you want to splice into the cooler input line. I shouldn’t say splice, I mean T-off the transmission, but I personally would like to see the temps coming off the transmission before the cooler, so I know how much heat is being generated and what the internal temp is close too. This way I’ll know if it’s close too damage. (I doubt I’ll ever reach that, but that’s what the gauge is for) I know the water temp sensor for the engine is on the thermostat right before the upper radiator hose where water returns to the radiator to be cooled. This gives you the temperature coming out of the engine. Why wouldn’t you want to do that with the transmission? I’m not sure what kind of pressure it gets, so maybe that’s part of the reason why.

I also don’t understand the difference between regular pipe thread and parallel pipe thread if someone wouldn’t mind explaining.

 

[alwaysFlOoReD]

Regular pipe thread, NPT, is cone or funnel shaped so it is somewhat self sealing. Parallel I'm not sure but I'm guessing needs an o-ring or gasket to seal.

 

[Curious Hound]

Wouldn’t you want to splice into the cooler input line. I shouldn’t say splice, I mean T-off the transmission, but I personally would like to see the temps coming off the transmission before the cooler, so I know how much heat is being generated and what the internal temp is close too.

That is my plan. The pictures I posted are at the transmission, right where the hard lines for the cooler connect. I need to look at it closer and figure out which line is coming out of the transmission and sending coolant to the cooler.

 

[scotts90ranger]

For curiosity sake I looked it up a little and apparently you're likely to see concerningly high and inconsistent temperatures on the cooler line... For Eric's purposes there's apparently an 1/8" NPT port meant for line pressure testing that is the best place for a temp sensor so that's probably what I'll do on the 4R70W. The other place some people put them is just put a bung in the pan.

 

[I support common sense]

Well, just to clarify my transmission is a 4r44e. Why is it that you would see inconsistent temps on the cooler line?