Coolant gauge = idiot light?

Status
Not open for further replies.
Joined
Mar 23, 2003
Messages
1,954
Location
Hopewell, Virginia, USA
Another thread on this forum asks about oil pressure senders and gauges in a Jeep Wrangler. The consensus is that the sender is for an idiot light, since the gauge maintains the same oil pressure reading no matter what.

Well, my '97 Escort wagon has always done the same thing on the coolant temperature gauge. The needle will rise slowly when the car is started cold, until about 10 minutes later it gets to a position a bit less than halfway. Then it stays there while the car is running, whether it's hot or cold, snowing or sunny. On rare occasions in extreme cold the needle will not get to that point but will stay a bit below. It never goes above that point, even when idling with the air conditioning on in an outdoor asphalt parking lot on a 100-degree day when the hood is too hot to touch.

This concerns me because I just put a head gasket in the car. That was, I believe, the direct result of spot overheating from a coolant hose clamp failure caused by a mechanic stripping the clamp upon reinstallation. The head gasket failed in two spots, but cylinder 4, the farthest from the water pump, was in the worst shape--and it's right by the coolant senders. The temperature gauge never read above normal (so for a while after the clamp failure I thought I had escaped head gasket damage). And I know of someone else with a similar but older Escort wagon who lunched a head gasket by overheating, but he said his temp gauge never went above normal either.

Here's my question. Does what I describe indicate that Ford used an idiot light sender for the coolant temp gauge? Or could the engine software intercede to prevent the needle from going above a certain point? (This would be to prevent needle fluctuations that would cause owners to return the car to the dealer for nuisance warranty claims, as has been commented on the oil pressure gauge issue.) Is there a fix, such as a different sender, that will give real movement to the temp gauge?

[ May 27, 2004, 11:13 AM: Message edited by: ekrampitzjr ]
 
-- does the fan run with the A/C on? They practically all do. Try idling on a hot day with the a/c off, and seeing if the gauge rises any before the fan turns on.

Since you say "coolant senders" I assume there are two? I don't know fords so this is a risky generalization but two-wire connectors run the ECM and one-wire connectors the gauge or fan switch (ground through head). Since one-wire connectors MUST ground through the head, it would do no harm to disconnect and ground said connector for testing purposes. Once grounded the fan will come on if it's a fan switch, and the gauge will go to its most extreme travel if it's a gauge sender. On GM low resistance == high temp and I think most others too-- so the needle should "peg" at the hot end. Regardless, the opposite result should happen if the connector is just left unplugged, dangling there.

Do this test with the key on; I don't think the motor needs to be running. If it is running and you disconnect the ECM sender you might get a check engine light.

Oh, and if the ECM runs the gauge, as some do, yes they can program it to be really "numb" in the middle.

[ May 27, 2004, 01:52 PM: Message edited by: eljefino ]
 
This car has two senders: one for the gauge (one wire), one for the ECU (two wires). They are side by side near the upper radiator hose exit from the head. The gauge never rises above the stated level no matter what the conditions are, and I have run it on a hot day with the air off. The cooling fan does come right on with the air on. Haven't tried disconnecting or grounding it while running, though.
 
I had the exact same situation with my 3.3L Caravan (except for the head gasket problems). The guage would not go above the halfway point under any circumstance. This changed on this past weekend though, when the van overheated because the rad fan gave out. I was travelling very slow on a rough road. I know now that the guage goes above half!
gr_eek2.gif


Another thing you could do to test the guage (something I considered doing myself) is to unplug the rad fan and let the car idle while monitoring the guage. I think eljefino's method would be better because it should not put the engine in danger of overheating.
 
There's actually three coolant temp senders for the Escort: 1) gauge, 2) ECU, 3) cooling fan circuit. The first two give a variable signal dependant on temperature, the third one is just an on/off switch.
 
That's interesting about your 1997 Escort and the "dummy" water temp guage. I have a 1996 Ford Contour with the 2.0L Zetec 4 and it's temp gauge is real. It likes to climb almost to the "L" in NORMAL before the fans come on and then it goes down to "A". And then the whole process repeats itself over and over in stop and go traffic. Heck, even with highway driving the temp gauge is at "M" usually but will fluctuate slightly depending upon the speed you're doing. My 2002 Ford truck has a "dummy" water gauge. It only goes up to the "comfortable" mid range and never higher even in the summer with the AC on in stop and go traffic. I think that the gauge will rise if the actual temp goes into the preset "danger zone". But then it's too late
frown.gif
.

Whimsey
 
My 2001 A4 has a coolant temp gauge with a dead zone as well. It's programmed to stay exactly in the middle of the scale as long as the coolant temp remains in the 80-100C range. I am however able to read the exact coolant temp through the digital climate control display that features a hidden diagnostics functionality.

My oil temp gauge does not have a dead zone though.
 
quote:

Originally posted by Whimsey:
...I have a 1996 Ford Contour with the 2.0L Zetec 4 and it's temp gauge is real. It likes to climb almost to the "L" in NORMAL before the fans come on and then it goes down to "A". And then the whole process repeats itself over and over in stop and go traffic....

I had a similar situation with my 91 Tracer (same chassis as the Escort). The temp gauge was normally at "N", but climbed past "M" when I was stuck in traffic. I was so alarmed that I spent a number of hours trying to diagnose the 'problem' before I got enough nerve to let it get higher and found the cooling fan kicked in at "A"!

I don't know if the temp gauge scale is more sensitive than other cars, or if Ford simply lets the coolant get hot before the fans kick in, but I find this unusual.
 
I suspect the coolant temp guage on my 2003 Camry is an idiot light with a needle! I can not belive that any car could have taht tightly regulated control over coolant temp. It stays exactly in the middle of the guage and never flucuates. I absolutely hate idiot lights and hate idiot needles even more!
 
The needle is likely deadened to be less sensitive when in the usual operating range. Prevents unknowledgable people from hyperventilating anytime a needle moves a bit.

Of course, I know folks who have installed guages without the "deadening" in late model F150's, and they more or less never move either! At the very least, much less than any other vehicle I've seen. Must be a efficient cooling system!
 
I was reding up today on RTDs which change resistance with temperature.

Some increase in resistance with temperature, while some decrease with temperature.

One of the suppliers was stating that he coupled them back to back for car temperature gauge applications, so that as the engine was warming, it would rise with engine temp. Then when it was in the "normal BAND" it would display almost zero sensitivity, and once above the normal band it would rise once again.

Apparently the car manufacturers would rather the needles sit dead stationary when the engine is within a normal range.
 
quote:

Originally posted by Shannow:
I was reding up today on RTDs which change resistance with temperature.

Some increase in resistance with temperature, while some decrease with temperature.

One of the suppliers was stating that he coupled them back to back for car temperature gauge applications, so that as the engine was warming, it would rise with engine temp. Then when it was in the "normal BAND" it would display almost zero sensitivity, and once above the normal band it would rise once again.

Apparently the car manufacturers would rather the needles sit dead stationary when the engine is within a normal range.


That would explain it well.

Note that if you have OBD2 interface, you can capture the actual temp from ECU. In my subaru, it fluctuates 180-212 F with temp gauge needle not making any movements.

This is silly becouse makes detection of subtle overheating (ie HG failure) impossible.

[ June 15, 2004, 02:13 PM: Message edited by: friendly_jacek ]
 
They did this on the F-150 oil pressure guage. It is just an idiot light. I assume the temperature is the same way. My temp guage rises to the normal position and then never moves. They claimed they had too many people concerned about low oil pressure because they saw it drop at idle in hot weather. It is another way of protecting the uninformed.
 
MNgopher, Shannow, and friendly_jacek are exactly right! One of my auto magazines has discussed this issue in a column. As long as the coolant temperature stays within the normal or "warm" operating range, the needle is electronically damped to remain centered.

This keeps the idiots from bugging the dealers about normal temperature fluctuations. It also keeps the rest of us from accurately monitoring our coolant temps. Yep, the gauge functions as little more than an idiot light.
 
On my previous vehicle, a 93 Explorer, after I changed the thermostat, the original gauge would slowly creep up to a certain point and then drop, then slowly go up again, over and over like a very slow metronome. I am assuming it was dropping right after the 'stat opened. I kind of liked that, you could tell in winter that the drop was steeper. I didn't change the gauge or sender, and the thermostat was not a cheapie and was the right temp range, so I don't know what caused the change. Never had a problem overheating or overcooling after the change. Before the change, the needle would just stay in the middle as described by others here.
 
rgl, I understand that all thermostats are not the same. The cheaper ones will snap open and shut at the specified temperature, leading to bigger fluxuations in coolant temperature. The better ones will open and close more gradually, keeping a more consistent temperature. So if you want to get rid of the fluxuations and if it's really worth it to you, get a better thermostat.
 
Thanks, but I sold the car a while ago, it had about 205 k on it and still running. Just thought it was an interesting observation. I forget the brand of the thermostat, but I do remember it was not a no-name. The old one was apparently stuck open and overcooling.
 
quote:

Originally posted by tmorris1:
They did this on the F-150 oil pressure guage. It is just an idiot light.

More than just the F-150...Ford hasn't used a real oil pressure gauge on any vehicle since somewhere in the early 90's, if not longer...

The coolant temp gauges are real, though...

I have no problem with a coolant gauge that reads the same during a range of "normal" temps, but I expect it to tell me when the vehicle is actually on its way to OVERheating...I DO have a problem with Ford's "better idea" of making an oil pressure gauge that reads "normal" no matter WHAT the actual pressure is...on my car, it read 60 lbs as long as the actual pressure was higher than 7
shocked.gif
...(I've since replaced it with a REAL gauge)
 
Status
Not open for further replies.
Back
Top