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Thermostat and Temp. Sending Unit

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Old 11-15-2000, 05:30 PM   #1
Triton46
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Well, its almost that time. I move into my new house in a few weeks and have already planned to do some maintenance to my car (now that I have the space).

First thing is the radiator flush. I am having a problem with the temperature guage, the car never leaves cold if I am driving around town. My first thought was the thermostat, however the car does have warm air coming through the registers after about 5 to 10 minutes. I am planning on replacing the thermostat, just to be safe but does anyone know how to replace the temperature sending unit? I understand that it is up from the thermostat, but being a shadetree I could use some help here.




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Old 11-15-2000, 05:47 PM   #2
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I had the same problem with my 94, the temp sender is right above the thermostat in a place where you can hardly get your fingers, but you can get a swivel socket, mine had problems with the wire, had to twist a certin direction to get it to read and when I did the gas mileage improved 2 mpg. The thermostat is easy just follow the top radiator hose to the block and take off the bolts. Make sure you get the old o ring off and put some sealer on the new one, don't over tighen thew bolts,


good luck




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Old 11-16-2000, 10:42 AM   #3
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Aren't there two separate temperature sensors, one for the computer and one for the guage? I think the guage sending unit is independant of everything else, so why did your mpg improve?

-Ben
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Old 11-16-2000, 11:16 AM   #4
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Ben,
It is the same one, if the computer is reading cold then the computer says you need more gas, thus the engine runs richer when it is actually warm, it will also make your O2's read to rich will give you a CEL sometimes. I wiggled the wires around and the guage started reading correctly and got 2-3 more MPG. I think there is also a TSB from ford on this subject.

Don




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Old 11-16-2000, 12:39 PM   #5
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I think I have the same problem. My temp gauge barely gets to the first mark (don't know if this is the first or 1/4 mark) and my wife complains that the heat is not all that HOT! I've already bought the thermostat but should I also look at the sending unit as well or replace it?




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Old 11-16-2000, 12:50 PM   #6
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Guys,

I need some help on the exact tools I will need for this project, as this is my first time changing the coolant on my own (let alone the thermostat and temperature sending unit).

I already know I need coolant, torque wrench, thermostat, temperature sending unit, gasket, 1/4inch drive ratchet, 10mm socket, wobble drive and socket extension.

1)Are there any other tools that will make getting the thermostat and temp. sending unit out easier?
2)Coolant: I went to NAPA today and saw the DEX-Cool type coolant from GM. The tech claimed I could use it in my 91 Explorer but I had heard that this coolant would mess up aluminum radiators. What is the best/cheapest coolant to use (as cost is a factor)?
3)What type of thermostat? The haynes manual says 196 degrees but I have seen 180 degrees as the one to use. Again, best/cheapest name brand.
4)Should I get the temp. sending unit from Ford or is there a cheaper/better alternative?




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Old 11-16-2000, 01:46 PM   #7
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sending units

As far as I know Ben is correct there are two sending units. The small single wire unit is for the gauge and the larger one with the multi wire plug is the ECT(engine coolant temp. sender), on my 91 the gauge unit is on the left and the ECT on the right. Make sure u seal the threads ont he senders(Ford has sealant on their replacement senders I think)

The gauge sender wont have an effect on the computer inputs at all.




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Old 11-17-2000, 10:50 AM   #8
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Thanks for the replies all.
In addition to these questions:
1)Are there any other tools that will make getting the thermostat and temp. sending unit out easier?
2)Coolant: I went to NAPA today and saw the DEX-Cool type coolant from GM. The tech claimed I could use it in my 91 Explorer but I had heard that this coolant would mess up aluminum radiators. What is the best/cheapest coolant to use (as cost is a factor)?
3)What type of thermostat? The haynes manual says 196 degrees but I have seen 180 degrees as the one to use. Again, best/cheapest name brand.
4)Should I get the temp. sending unit from Ford or is there a cheaper/better alternative?


How much will a thermostat and TSU cost from Ford or should I look elsewhere? I read a post yesterday that said Fords thermostat has some sort of bleeder hole to allow air to escape, without it your truck will run hot. Anyone?




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Old 11-17-2000, 11:04 AM   #9
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I had the same problem w/mine last year. Put in a Stant(sp?) 195 degree. Make SURE you get the rubber O-ring (Stants is in the box, NAPA is separate, but's that's another Ford story) runs about $6. Didn't mess with any sending units. After the stat change, runs at top dead center of the gauge, added 2-3 mpg.
Do the the stat first, then the sending unit if that doesn't solve it.
Special tools ? just lotsa patience !. A toggle(Ujoint) for your ratchet comes in handy for the bottom bolt. It helps to also take off the serp belt first, and replace it too if need be.
Good Luck. This won't be the hardest thing you will ever do to your ride.
Let us know


[Edited by kps36 on 11-17-2000 at 09:06 AM]




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Old 11-17-2000, 11:05 AM   #10
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Triton use the 195 tstat, they do have a bleed hole and it should point up when it is installed, make sure you get a new o-ring type gasket with it.

tools nothing special- it is difficult to get to the housing but just takes patience, and some contorted hand motions. I think you will need an open end wrench (10mm) to get to one of the housing bolts. Also a deep socket to get the sender out, dont know the size its close to an inch I think.

Ive used non ford tstats with no problems.

take your time have fun and good luck,




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Old 11-17-2000, 11:08 AM   #11
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Thanks guys!

How about questions 2 and 4, would really appreciate your opinions. Thanks!




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Old 11-17-2000, 11:13 AM   #12
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I dont know anything about the DEX coolant, I use Prestone why? Dont know, just usually what I pick up.

Senders- if I needed a sender I wouldnt be afraid to purchase them from someone other than Ford. I usually go to a NAPA auto. Others may have another opinion.




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Old 11-17-2000, 07:55 PM   #13
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Which Prestone do you use? I saw some at K-Mart in a yellow can (the greenish looking fluid) then saw some at NAPA in a silver can (reddish looking fluid). Basically, the reddish fluid is Dex-Cool.

Has anyone used the reddish fluid? Is it safe for 91 Explorers?




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Old 11-17-2000, 11:42 PM   #14
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The pink radiator fluid should not hurt the Explorer, or the aluminum, since just about everybody uses aluminum, now.
It would be a good idea to change the serpentine belt, at the same time. Removing it will also give you a little more room to work. Removing the air tube from the air box to the throttle body helps, too.




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Old 11-18-2000, 11:14 AM   #15
Triton46
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I was reading in the Haynes manual on the procedure to flush the radiator. At the refilling part it says to reinstall the block drain plug(s) when refilling, but never told you where they are or to take them off in the first place (Thanks!).

Can someone tell me where the block plugs are? After draining the block, I should be able to keep adding fluid to the radiator until the whole system is full, right?




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Old 11-18-2000, 11:42 AM   #16
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I just replaced my thermostat

I just replaced my thermostat and it solved the gauge not going much past the first mark. It also blew heat but took awhile. The service manual recommended checking the thermostat first. I simply replaced it and fortunately it works perfect now. Hardest part was getting to the 3 bolts. My 10mm ratchet w/ extension could only get to one bolt. It probably wouldv'e been easier if I took off the belt but I was too lazy to do that. I was thinking of replacing it also with the pink coolant but since it was already using the old green type I re-filled it with that. Good luck!




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Old 11-18-2000, 11:46 AM   #17
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Thumbs up

Prestone makes a flush kit it mite pay for you to buy it if you plan on keeping the truck. It compleatly flushes raditor and block without removing plugs.
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Old 11-18-2000, 01:55 PM   #18
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I just went out to check out where the bolts are for the thermostat...holy cow! That bolt on the left as you're facing the front of the engine is tight, looks almost impossible to get at. I also found the 2 temperature sending units on the top of the engine. I will most likely replace these first and see if my temperature guage goes back to normal. Then if it doesn't, I will replace the thermostat while changing the fluid.

I went out to look at the temp senders and the one on the right appears to be partially unscrewed. I found the part number for one of them DY-681, does anyone know what the other one is?


Ric,
Yes I plan on using the Prestone kit, but you must first drain the radiator. Most of the fluid is in the block, and the Haynes manual mentions two block plugs to drain it but does not tell you where.

In order to drain the fluid completely, I would have to flush with fresh water over and over until all of the fluid in the block is water. Can anyone tell me where the block plugs are?



[Edited by Triton46 on 11-18-2000 at 02:04 PM]




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Old 11-19-2000, 06:38 AM   #19
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Triton,
I think the block plugs they're referring to are the plugs (sometimes plastic) that are on the radiator bottom-half side. I tried doing that one time on another vehicle and had a hard time putting the plug back (the plastic piece had stripped off).
As for the T/stat and sender units, I would replace the T/stat first. First, the part is much cheaper and second, in my little experience, mechanical parts fail more often and frequent than electronic parts.
I would leave the sender unit alone for now if your gauge moves even just a little bit. If the T/stat replacement doesn't solve it, it's easy to go back and check/replace the sending unit.
The Prestone (TM) kit is worthwhile to install cause it allows you to perform a backflush on the system (forcing water the opposite way - into the output of the heater core and out the input side. I have an '85 Daytona and a couple years ago the heater would not blow hot air. Every mechanic I brought it to said I had to get a new heater core - $$$. Finally one day, with nothing to loose, I performed a back flush. Fixed it. Best $5.00 I've ever spent.

[Edited by config on 11-19-2000 at 08:56 AM]




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Old 11-19-2000, 08:32 AM   #20
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There are no block plugs on the 4.0 The instructions in the chilton, Haynes manuals are generic for a bunch of different engines and most times are not edited to be specific to the vehicle/engine.

The valve on the lower radiator doesnt need to come out just turn it until it is open.

I would replace the t-stat first. If the gauge doesnt move at all then it could be the sender or gauge- sender should have 73 ohms resistance low, 9.7 high.




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