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Discussion Starter #1
I am trying to sort out a cooling system problem on a car I purchased recently. I have noticed that at operating temperature, the temp gauge on the dash seems amazingly steady, absolutely dead center, no matter if I'm climbing a good long hill with a/c running on a hot day, or on level in the cool evening. That could seem like a good thing, but....

I have had two or three occasions of coolant loss appearing on the ground. Once the source was the overflow reservoir, rapid dripping, and that occurred right after I'd topped off the radiator and the reservoir (between the max / min marks) for the first time after acquiring the vehicle. Then I headed off on a short road trip, beginning with a steady uphill gaining about 2000 feet in 15 miles. I replaced the radiator cap at the first opportunity. And didn't see coolant leaking again.

Recently though, on a hot day, after driving about 3 miles, I parked and noticed a steady small stream hitting the pavement, more flow than the first case, appearing in the vicinity of the reservoir but I did not have the opportunity right then to look for the source or confirm if it was coolant or a/c condensate...the a/c had been on. Temp gauge showed normal, as always. Later, at home with the engine cooled down I discovered the radiator needed coolant and the overflow was empty.

Both times the temp gauge clearly showed the very same dead center reading. Thus I began to suspect the temp gauge sending unit was faulty and decided to splurge $10 to replace it to be on the safe side. That seemed like a good start.

I bought a new sending unit at a local Napa store, only to discover that I can't find where the thing goes on the engine. I've studied the factory manual for clues and found none. There IS a sensor right beside the thermostat housing, but looks nothing like what I bought, and I did check back with the store to confirm that I have the correct part, or at least the number on the box is correct. The Napa part is much smaller in diameter, and length, and has one single threaded post on the top of it.

The manual does show a drawing of the "engine coolant temperature sensor" (page 14-67) which matches what I found on the engine, but again this does not resemble the new part.

Did I simply get a box with the wrong part inside? Or is there some other location for the gauge sending unit?

My sense is that the engine is not overheating, but I can't say for sure. The coolant loss like this suggests a head gasket or water jacket problem, but the engine runs great, 25mpg mileage, no visible exhaust signs, and the CA emissions test was sparkling clean, according to the tech "as good as it gets". The test for combustion gas in radiator was clean.

Any ideas on what might be going on?

Thanks for any help.
 

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Does the one in your engine look like this?


NAPA part number DEM TS10019
 

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They probably gave you the TS6660


which is a sender for a temp gauge on vehicles that use a separate one for the PCM and the gauge. My '90 2.5T had both.

Try unplugging your sender by the thermostat and see if 1)engine dies, 2)fans automatically start, and/or 3)temp gauge goes to 0.
 

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IIRC, there is not seperate gauge sending unit on this vehicle. The gauge gets its information from the the engine coolant sensor shown in Ray's post above. the ECM passes it along to the BCM via a data bus and then it passes to the instrument panel.

I will say that on my 96, the gauge is very solid toward the center under all conditions. However, I had an overheat situation due to a failed water pump (lost an excessive amount of coolant) and the alarm warning bell went off and the gauge was at 7/8ths and heading for hot when I shut it down.
 

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Discussion Starter #5
Thanks for the reply. Yes, that looks about right - for the one on the engine, right beside the t-stat housing. I pulled the connector and confirmed two separate terminals. The factory manual calls this "coolant temp sensor" which I presume is what supplies information to the computer.

I just called Napa again and confirmed that they show a coolant temp sensor as something different than the part I bought. I'm looking for the sending unit for the gauge on the instrument cluster, just to be more certain that what the gauge is showing is accurate. I can't locate that on the engine, even with the help of the factory manual.

The "sending unit" from Napa is thinner and has a single threaded post on its top.

I want to clarify what the true engine temp is before I change the t-stat, in order to help troubleshoot the coolant loss question.
 

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I will say that on my 96, the gauge is very solid toward the center under all conditions. However, I had an overheat situation due to a failed water pump (lost an excessive amount of coolant) and the alarm warning bell went off and the gauge was at 7/8ths and heading for hot when I shut it down.
On my '96, the gauge religiously stays about a needle's width below halfway. I once blew that plastic restrictor in the heater hose and I saw the gauge climbing rapidly. As with John, mine was almost on HOT before the alarm sounded.
 

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Discussion Starter #7
Ray-you're right about the TS6660, that's what I have, and the pic looks right.

John-What I found in the manual matches what you wrote about how the gauge gets information.
 

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Thanks for the reply. Yes, that looks about right - for the one on the engine, right beside the t-stat housing. I pulled the connector and confirmed two separate terminals. The factory manual calls this "coolant temp sensor" which I presume is what supplies information to the computer.

I just called Napa again and confirmed that they show a coolant temp sensor as something different than the part I bought. I'm looking for the sending unit for the gauge on the instrument cluster, just to be more certain that what the gauge is showing is accurate. I can't locate that on the engine, even with the help of the factory manual.
I believe that the one by the t-stat housing is the only one on your engine.
 

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Discussion Starter #9
I believe that the one by the t-stat housing is the only one on your engine.
That's the way the manual suggests, but then why would Napa also show the TS6660 for this engine?

If my gauge is showing me the very steady temperature, should I doubt the accuracy of my coolant temp sensor? I don't want to waste money on that if this one is fine. I can certainly return the TS6660, it's just been out of the box on my desk, not used.
 

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If my gauge is showing me the very steady temperature, should I doubt the accuracy of my coolant temp sensor?
Try blocking the airflow with cardboard or unplugging the cooling fan and see if the gauge begins to climb.
 

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I suspect that in 1995 there was a seperate gauge sendor unit like what you bought. I've noticed over the years that when a design changes, the parts stores don't often keep up, and it is possible that their catalog is wrong. Another possibility is that the US may have been the first to get the design change but perhaps models sold in other countries did not get the change until a year later.
 

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Try blocking the airflow with cardboard or unplugging the cooling fan and see if the gauge begins to climb.
Of course the SES light will come on immediately. Be sure you can clear it. :)
 

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Discussion Starter #14
Of course the SES light will come on immediately. Be sure you can clear it. :)
Hmmm, I have no way to clear the llight. Are you suggesting that the light will come on just if the temp climbs? I would think that at minimum, the gauge would have to be buried in the hot zone to trigger the light. If I do block the airflow or unplug the fan, I'd shut down as soon as I saw the gauge needle climbing higher than usual, just to confirm it's responding.
 

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Hmmm, I have no way to clear the llight. Are you suggesting that the light will come on just if the temp climbs? I would think that at minimum, the gauge would have to be buried in the hot zone to trigger the light.
Unplugging the fan may bring on the light. I didn't think so though. Unplugging the sensor would I'm sure.
 

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Discussion Starter #17
With a precision cut (;~) piece of cardboard slipped in front of the radiator (between rad and a/c cooler) I drove about 5 miles or so including up a sustained hill, and the gauge stayed fixed at the midpoint. I stopped to look for coolant leak and there it was, definitely coolant, dripping pretty fast. Looked like it was coming from the radiator. I then took out the cardboard and drove home.

Back home, idling in the driveway as I tried to get a better look at the source of the leak, I finally heard the fan come on so checked the gauge and it was elevated a bit, just a tad above the midpoint. So I guess that test showed the sending unit may be ok, but the radiator probably not.

Should I simply replace the radiator, or is repair a sensible option these days? I can do the R&R myself.
 

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With a precision cut (;~) piece of cardboard slipped in front of the radiator (between rad and a/c cooler) I drove about 5 miles or so including up a sustained hill, and the gauge stayed fixed at the midpoint. I stopped to look for coolant leak and there it was, definitely coolant, dripping pretty fast. Looked like it was coming from the radiator. I then took out the cardboard and drove home.

Back home, idling in the driveway as I tried to get a better look at the source of the leak, I finally heard the fan come on so checked the gauge and it was elevated a bit, just a tad above the midpoint. So I guess that test showed the sending unit may be ok, but the radiator probably not.

Should I simply replace the radiator, or is repair a sensible option these days? I can do the R&R myself.
Modern plastic/aluminum radiators are pretty much a throw away item. What most DIYers are doing is to go online, find an Advance Auto Parts Coupon code, go to the online store, purchase the item using the discount code, and order the part for pickup at the local store. The coupon code that I last used was CCABIN and it $40 off any 1 purchase of $100 or more. If that works, it is a good deal and you should get that radiator for around $100.

They are a nuisance to replace because of the condenser to radiator bolts that are tough to access unless you take off a lot of the front grill/fascia trim. Otherwise, that should take care of you. Check the radiator hoses too.
 

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Discussion Starter #19
Thanks John. I'd have to have it shipped, no stores anywhere close (CA). Having a little trouble with their website, but it does look like the coupon code they offer would get it to about $100, just as you said, free shipping, no sales tax. Good tip, I appreciate that.

After a brief look at the vehicle, I think you're right too about the PITA to make the swap. Looks a lot harder than the last one I did, which was probably my 1990 Grand Caravan where the engine room isn't so squashed.
 
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