Thermostat replacement success- leads to questions

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Thermostat replacement success- leads to questions

delco1946
 So I successfully replaced my thermostat which the correct type-which is of course rare and expensive  (Joy! Lol). My engine appears to be much happier temperature wise. Butttttt it did raise some other questions.  I just recently started using my dual tanks as I was told they didn’t function when I bought the truck but either they do 1) and the gas gauge just doesn’t read correctly on the rear tank or else 2) when I switch to the rear tank perhaps somehow it continues to pump fuel from the front tank but the gauge reads differently? I’m not sure which is more likely. Anyway I noticed when I switch between tanks the temperature gage would actually change settings which seems strange as it shouldnt  be related to what tank the fuel is coming from but it does lead me to question the accuracy of the temperature gage. Any ideas as what might be happening? Also  there appears to be several vacuum connections to the external housing on the thermostat elbow and I can’t seem to find out what those are. Where they connect into the housing when I had it out they look pretty corroded and I’m questioning how will they function but I can’t figure out what on earth they are-there probably for an emissions system since they would activate when the temperature of the engine is higher I’m guessing? I’m going to take a picture. They Are the blue and white things in the picture.
1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6 tranny
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Re: Thermostat replacement success- leads to questions

Gary Lewis
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First, congrat's on the thermostat change.  

As for the gas gauge, there are two separate issues here:

1. The reason that flipping the switch to the other tank changes the temp gauge is that the fuel, temp, and oil pressure gauges are fed by the instrument cluster voltage regulator, ICVR.  And if one tank is relatively full and the other relatively empty that will make a big change in the current draw through the ICVR, which changes the voltage to the other gauges.  That's not unusual but there's a way around it if you want to go there.

2. It is possible it continues to pump from the front tank when you flip the switch.  You should have the 3-port valve, and those can certainly fail and not switch from one tank to the other.  You can check this by pulling the fuel line going to the front tank and trying to drive the truck with the switch flipped to the rear tank.

On the vacuum connections, I really can't tell anything from your little picture.  I've blown it up a bit below, but that's getting pretty fuzzy.  In any event, there were some extra vacuum devices on the 81's, and I suspect the one you are asking about is the temperature-switched valve.  I don't remember exactly what it did, but you do not need it if you aren't running the full emissions package.

If you had a picture of where those lines go we could probably figure out exactly what you have.  But, before posting more pics please go here and read up on how to post them so we can actually see them well: Bullnose Forum/Forum FAQ's.

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker in front & 10.25 Spicer/Trutrac in back, & EEC-V MAF/SEFI
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Re: Thermostat replacement success- leads to questions

ArdWrknTrk
Administrator
In reply to this post by delco1946
One thermal vacuum valve probably controls EGR, and the other, over temperature high idle by supplying full manifold vacuum to the advance can, instead of through the restrictor.
 Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with an Edelbrock 1826 and Performer intake.
Too much other stuff to mention.
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Re: Thermostat replacement success- leads to questions

FuzzFace2
On the 3 port fuel valve 1 thing you can do with a helper is get under the truck and hold you r hand on the valve. Then have the user with key on flip the switch between the 2 tanks.
When this happens you should feel & maybe hear the valve switch between the tanks.

1 step more would be to remove all hoses and put a long hose on the outlet.
With helper blow in the long hose and feel what port the air comes out then switch tanks and see if the air now comes out the other port.
If the air does not switch ports valve is no good.

I just did this to my 81 F100, when feeling the valve it did not "click".
I then pulled it and bench tested and could barely feel the "click" and the air test failed so I replaced the valve.
BTW I did not know if this worked or not as the duel tanks came from my parts truck but 1 tanks was empty so thinking it did not, it should now.

As for the temp gauge Gary could be right but I would also check all the grounds mainly the body to frame and frame to battery, may even check battery to motor when at it.

On the vacuum lines do you have a sticker on the radiator support showing the vacuum lines?
Dave ----
81 F100 flare side 300 six/T18 project
http://cars.grantskingdom1.com/index.php/1980-Ford-F100?page=1
81 F100 style side 300 six/SROD parts truck
http://cars.grantskingdom1.com/index.php/1981-Ford-F100
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Re: Thermostat replacement success- leads to questions

delco1946
Sorry for the delays in responding. I’ll try and post some pics soon. As to the tank issue I’m thinking the easiest thing will be to fill a gas can and then drive until I run outa gas then switch tanks and see what happens. If nothing I’ll still have gas in the can to get me home!

Also I will check my wiring this weekend. My horn started working for a bit and is now out again which suggests a wiring issue. I also have all my emissions stuff as it’s just too much for me mentally to handle removing it all right now.
1981 F250 Ranger XLT 4x4 trailer special 351M, and auto C6 tranny