thermostat question

[sambudo]

Originally Posted by swamp rat

The 5/8 and 3/4 heater hoses will be as hot as your water temp, if a 190 thermostat then at least that hot probably even a bit hotter because the water that flows to the heater just went thru the engine. The Heater core will always have hot water flowing thru it.

The bottom lever controls a flap door inside the heater body, the door is what allows the air to flow across the heater core. If i remember correctly the air flows from the blower, then to a door which allows ether, none, all or part of the air to flow across the heater core, if it allows none then the air goes around a bypass and comes out ether the heat or defrost outlets depending on the position of that control. The door is moved depending how far you push the lever to the hot or cold side, and by varying the air across the heater core is what controls the temperature.

The temp gauge is very possibly the sending unit which is usually screwed into the head but not sure on your engine. The sending unit is not suppose to have Teflon tape on the pipe threads as the threads are the ground. Auto parts stores sell sensor safe thread sealer made for this application.

the lever that open and closes the flap is missing, also the hoses under the dash that would transfer the heat are also torn up, need replacing. Not sure if i have a heater switch, not sure how the heat turns on. regarding the sending unit, can i just replace this? Will water leak out if i remove this?

[sambudo]

Originally Posted by Andy4639

Can U explain this a little better.
What heater hose under the dash are U speaking of?
The lever missing is it the fan switch? I'm not real sure for a non AC truck.

The temp switch is missing. Whichever hose is under the dash.

[swamp rat]

I think the hose under the dash your referring to is just a duct hose that runs from the heater box up to the defrost vents, About maybe 2 1/2" in diameter. they usually rot out and need replacing, the good news is they only cost about $13 and some change, call Wes at Classic Heartbeat, he's a board vender here on the forum and he lives in Washington state. http://www.classicheartbeat.com/

Per the picture above, the top lever is the one that moves a flap door that directs heated air to ether the floor heat port or the defrost ports.

The middle one is hooked to a 4 position switch that controls airflow ie the electric switch, (Off, Low, Med, Hi).

The bottom lever that is missing per your post is the Temp, the one i was talking about earlier that directs the air ether over the heater core or around it.. The opposite end of the cable should be hooked up to that flap door lever sticking out of the heater box, i just cant remember off hand if its on the top of the box or where.

Brand new replacements for the heater control unit (picture above) are i think over $200 but you could score a used one in the parts part of this forum for much less.


It is common on these old trucks to have never had these cables or controls lubed so sometimes the control lever(s) may bind up break and then need replaced. Look under the dash and follow the cables to where they connect to the heater box, move the lever and look at the other ends to see if the actuators are moving.

The sending unit is a temperature sensor and is threaded into a hole that is in the water jacket so yes if you pull it out the water will come out. so its best to drain the radiator..Remember my post above and the special thread sealant? You haven't added antifreeze yet have you? if you did just catch it all in a bucket, I hook a length of rubber hose to the drain valve to direct it to a bucket..

I cant see your truck so i cant look it over and see if i think any of the wiring is messed up, but i'd probably do that before i went and ordered a new temp sensor, Do all the other gauges and lights work on the gauges?

[sambudo]

Originally Posted by swamp rat

I think the hose under the dash your referring to is just a duct hose that runs from the heater box up to the defrost vents, About maybe 2 1/2" in diameter. they usually rot out and need replacing, the good news is they only cost about $13 and some change, call Wes at Classic Heartbeat, he's a board vender here on the forum and he lives in Washington state. http://www.classicheartbeat.com/

Per the picture above, the top lever is the one that moves a flap door that directs heated air to ether the floor heat port or the defrost ports.

The middle one is hooked to a 4 position switch that controls airflow ie the electric switch, (Off, Low, Med, Hi).

The bottom lever that is missing per your post is the Temp, the one i was talking about earlier that directs the air ether over the heater core or around it.. The opposite end of the cable should be hooked up to that flap door lever sticking out of the heater box, i just cant remember off hand if its on the top of the box or where.

Brand new replacements for the heater control unit (picture above) are i think over $200 but you could score a used one in the parts part of this forum for much less.


It is common on these old trucks to have never had these cables or controls lubed so sometimes the control lever(s) may bind up break and then need replaced. Look under the dash and follow the cables to where they connect to the heater box, move the lever and look at the other ends to see if the actuators are moving.

The sending unit is a temperature sensor and is threaded into a hole that is in the water jacket so yes if you pull it out the water will come out. so its best to drain the radiator..Remember my post above and the special thread sealant? You haven't added antifreeze yet have you? if you did just catch it all in a bucket, I hook a length of rubber hose to the drain valve to direct it to a bucket..

I cant see your truck so i cant look it over and see if i think any of the wiring is messed up, but i'd probably do that before i went and ordered a new temp sensor, Do all the other gauges and lights work on the gauges?

Well good news and bad news! First the good, I checked the heater blower and it worked direct link from the battery to the motor. The fuse to the heater looked good, but I replaced it anyway with a 20a. I checked all the cables, and all are still hooked up and seem to operate correctly, except the one with the missing lever.

The middle one that is hooked to the 4 position switch seems to only work in the off, and high position! I don't think I have a low or medium air flow option. The cab warmed up pretty good.

The hose I have been referring to directs the air flow to the defrost, this will need to be replaced. Rick at Chevy Metal in Vancouver,Wa. gave me a small section that I think might work. Thanks,Rick!

I still need to trouble shoot my temp sensor sending unit. Yes I put Antifreeze back in, as the other day it wasn't leaking. Seemed to be holding water and pressure fine. So I put it back in. Well tonight after running it for awhile I noticed it was leaking from the same spot, bottom rad hose. I can't get it to seal correctly. any suggestions? The hose only fits at an angle, I've tried putting it on several ways? I'll have to drain and try again tomorrow night.

Regarding my temp gauge, Rick said it might be possible that the needle pointer fell off. So some weekend, I'll pull off the gauge cluster and check this out. If it's bad possible repair it or replace it. Thanks swamp rat and others that have been guiding me thru this little project. Much appreciate all of you!

[swamp rat]

Originally Posted by sambudo

Well good news and bad news! First the good, I checked the heater blower and it worked direct link from the battery to the motor. The fuse to the heater looked good, but I replaced it anyway with a 20a. I checked all the cables, and all are still hooked up and seem to operate correctly, except the one with the missing lever.

The middle one that is hooked to the 4 position switch seems to only work in the off, and high position! I don't think I have a low or medium air flow option. The cab warmed up pretty good.

The hose I have been referring to directs the air flow to the defrost, this will need to be replaced. Rick at Chevy Metal in Vancouver,Wa. gave me a small section that I think might work. Thanks,Rick!

I still need to trouble shoot my temp sensor sending unit. Yes I put Antifreeze back in, as the other day it wasn't leaking. Seemed to be holding water and pressure fine. So I put it back in. Well tonight after running it for awhile I noticed it was leaking from the same spot, bottom rad hose. I can't get it to seal correctly. any suggestions? The hose only fits at an angle, I've tried putting it on several ways? I'll have to drain and try again tomorrow night.

Regarding my temp gauge, Rick said it might be possible that the needle pointer fell off. So some weekend, I'll pull off the gauge cluster and check this out. If it's bad possible repair it or replace it. Thanks swamp rat and others that have been guiding me thru this little project. Much appreciate all of you!

Could it be the wrong hose??

If your gonna drain the coolant go ahead and swap out that sending unit, its not that expensive, be sure to get some sensor safe thread sealant in the sealer section of the auto parts store.. If the lower hose is old just replace it too, if its new or close to now then clean the hose and radiator inlet of any water scale build up and wipe it nice and dry, the hose should not be hardened from heat or deformed from the hose clamp compressing on it.

I had one time i was dealing with the same lower hose leak but couldn't get a hose right away and still needed to drive the truck, so i cleaned up the hose and radiator then smeared a bit of red high temp silicone in the radiator inlet slid on the hose and clamped it down then let it sit over night before filling it. it got me home and then some.

[sambudo]

Originally Posted by swamp rat

Could it be the wrong hose??

If your gonna drain the coolant go ahead and swap out that sending unit, its not that expensive, be sure to get some sensor safe thread sealant in the sealer section of the auto parts store.. If the lower hose is old just replace it too, if its new or close to now then clean the hose and radiator inlet of any water scale build up and wipe it nice and dry, the hose should not be hardened from heat or deformed from the hose clamp compressing on it.

I had one time i was dealing with the same lower hose leak but couldn't get a hose right away and still needed to drive the truck, so i cleaned up the hose and radiator then smeared a bit of red high temp silicone in the radiator inlet slid on the hose and clamped it down then let it sit over night before filling it. it got me home and then some.

Actually the hose is new, I replaced it the other day. Seems to fit same as the other old hose. I cleaned up the radiator when I had it out recently. I think it's a strange fit. I think if I can get another hand, I might be able to get a better fit and clamp it on. Good suggestion on the sensor, I'll pick up that sending unit along with the special sensor safe thread. Then install that tomorrow.

[sambudo]

Looks like I don't have a stock radiator. The outlet to engine OD is approx. 2.5", the inlet to engine is approx. 2.875" The stock hose won't seal correctly. Has anyone had success with radiator hose reducer bushings? If so what brands do you recommend? Gates?

Rubber reducers that are inserted into the inside of a radiator hose to reduce the ID of the hose for a proper fit to the connection. Flange of reducer will prevent slippage into hose. Makes any stock hose into a “Dual ID” hose.

[swamp rat]

Never herd of it..... Never seen one... I think i'd try and use 2 hose clamps..

I did google " radiator hose reducer bushings" tho and found this on Ebay, i was also noticing the bell type blue reducers but had not enough time to research it for size. I would think it couldn't hurt to try.

http://www.ebay.com/bhp/radiator-hose-reducer

[MARKDTN]

Originally Posted by sambudo

Looks like I don't have a stock radiator. The outlet to engine OD is approx. 2.5", the inlet to engine is approx. 2.875" The stock hose won't seal correctly. Has anyone had success with radiator hose reducer bushings? If so what brands do you recommend? Gates?

Rubber reducers that are inserted into the inside of a radiator hose to reduce the ID of the hose for a proper fit to the connection. Flange of reducer will prevent slippage into hose. Makes any stock hose into a “Dual ID” hose.

I only use Gates belts and hoses. I have had discount brands that did not go the distance. I have never heard of reducing diameter with a bushing on a radiator hose. You might try a hose for a 73-87 with 6 cyl and see if it is the correct size at the radiator. If that doesn't work, I would suggest going to a good parts store and seeing if they will let you poke around in the back and try to find a hose that will fit without reducing it.

[Ironangel]

I had the same problem your describing with the lower hose on my 72 and apparently the previous owner did too because there was extension soldered to the 90 degree outlet that angled slightly upward to accommodate the hose that angled slightly down...When I replaced the radiator the (new) lower hose would not properly fit the 90 degree horizontal outlet properly...My fix was to trim the upper lip of the lower hose to allow the lower half of the hose to obtain a full bite onto the outlet..."Wahlah!" No more leaking... I essentially mitered the end of the hose to allow a full bite onto the outlet...I use Gates rubber from NAPA and the part number is correct for that application...Apparently, some factory radiators had angled lower outlets...? Hope this helps...

[sambudo]

Thanks everyone, I finally found a gates hose that is reduced on the radiator outlet and lslightly larger where it goes into the clock. So far it is holding water, although I have only ran it for 30 mins or so two seperate times.

I still have the temp gauge problem. I think I will pull the gauge cluster and rebuild the temp gauge. Again thanks for all the insight.

[swamp rat]

Glad to hear your getting things solved!

[MARKDTN]

Originally Posted by sambudo

....The middle one that is hooked to the 4 position switch seems to only work in the off, and high position! I don't think I have a low or medium air flow option....

This is likely the blower relay. I believe it is on top of the heater box. When you are in high speed it gives direct 12V to the blower. At the middle switch positions it sends power through the resistor(s) to give lower speeds. It could also be that the resistor is unplugged or all bad, but most likely it is the blower relay.

[Murphy IRE]

I'll piggy back on this one, there may be some overlap. Gertie is not my dd.
She has a 400cid, she heats up in 10 minutes and she will get the cab toasty warm after the 10 minutes. My vacuum values are dead, so I put in a gate value in line; so it's on or off, otherwise I could have heat year round (Not good over 90 - most of the summer). I have a big 4 core oversized radiator. The engine it's self runs hot. I had to put in a spacer for the carb heat problem (That's a separate thread). I think she has a 180 to help with the summer heat, but she runs really cold in the winter. My guages work. Last week (really cold) she heats up fine, but once I get on the freeway the Gauge drops to below cold. Should I do the trucker trick and block the radiator to retain heat?