I may need to replace my temperature sensor and was wondering if it can be done without draining the coolant. I am pretty sure I know the answer is no but thought that I would see if anyone had any hacks. I even thought about tilting the truck to the driver's side to get the hole up higher but something tells me that will not help much.

I was able to use a similar method when replacing my drive shaft output seal and did not spill a drop!

If not it will not be the end of the world as it would not hurt to flush the radiator.

I say may need to replace it because I need to test the gauge and make sure that is not the problem. If by chance the gauge is bad is there a way to test the temp sensor without removing it?

Thanks

 

Are you sure it is the sending unit??? to check, take the new one, heat it up in warm water then hook the wire up and ground the unit then see if the gauge moves. warm or hot water.. sensors are pretty reasonable. very seldom go bad though..
If it was mine I would start in the morning when really cool,,,,,wrap a rag agound the base, have the new sensor ready to screw in, then, un screw the old and then real fast, screw in the new and torque it down. Oh yea do not take the cap off as it should cause a suction and maybe help slow the flow.
On a 300, shuld be realitively easy up top by the upper hose.
My .02 worth on this...

 

Thanks for the info.

So I did just test my gauge and it seems to be working. I grounded it out and turned the key and the gauge pegged out and then came back down after turning the key to off. I am about to run to the store for my wife so I may just take the truck to let it warm up some just to make sure that there wasn't a bad connection between the sending unit and the wire. If it doesn't work then I will give the quick swap a try.

 

Not true that is the sensor for the computer on feed back systems (84-86) and EFI (87-97).
I am sure the poster knows where the temp gauge sender is as he tested it but for the one that dont know where it is.

On the right side (when sitting in the driver seat) of the block to the rear kind of under the manifolds you will finf the temp gauge sender and a push on wire.
Yes this push on can have a bad connection and either not read right or not at all.

I also dont see anyway to change it out with out loosing some coolant .
I will say if you dont drain the system to leave the radiator cap on and tight.
It can be a PITA to get the new sender screwed in as you cant really see where the hole is.
Also DO NOT put tape on the sender as it needs to ground to the block and the tape can stop that from happening.
Dave ----

 

Thanks Dave. Good info. You are correct, my sender is located on the passenger side right behind the exhaust manifold. I did run the truck last night after confirming the gauge worked and the gauge did not move. I did not "clean" the connection but I assume that removing and replacing the wire's plug a couple of times like I did would have knocked enough crap off of the post to make the connection. Thanks for the no tape tip. The new sender has what looks like some pipe dope on it already but not the entire way up the threads. Thinking about that could the current sender have rust between it and the block that may cause the issue? I guess that I could test it by putting a definite ground on the plug housing and seeing if anything changes.

From what I can see looking into the radiator hole the water does not look cloudy so if I don't find any change with the "grounded sensor test" I may just try and do the quick swap and see how much of a mess I can make. LOL
If the sensor works with the housing grounded I will probably just leave it like that until I either am ready to start major restoration or have to drain the coolant for some other reason. If it is not grounded that means I will have to take time to clean up the sensor port and that would not be very practical with a steady flow of coolant....however, a steady outward flow would help keeping crap from falling back into the block...

We shall see.

 

Sorry guys, I was going by the OP's signature which says;;;;

1975 Ranger cab long bed over a 1977 chassis 2WD
300 Inline-6, 4.9L
I must have missed something...I may need to improve my reading skills..LOL
Alex

 

That little blob on the new sender is sealer just screw it in.
I have not had one "not ground" when screwed in but if you want to try and ground the outside go for it.
I would also say if you are going to do that take a ohm reading on the sender stud to ground when cold then get the truck up to temp and take the reading again.
If the sender is working as it should the readings should be different between cold & hot.

I just know when talking dash gauge for temp the sensor or sender is on the side if the block and only has 1 threaded stud out the top.
The sensor up by the Tstat has think 3 or 4 wires in it and is for feed back to the computer, feed back or EFI systems.
The computer needs to now ASAP when the stat opens and why it is at the stat, to change loops from close to open for smog control.
Computer then looks at the O2 to adjust the AFR and the temp at the stat to make sure it can in open loop.

On the feed back trucks 83-86 with a 300 six, you can pop on a non-feed back carb & dist. and remove the computer and all wiring and have a good running motor again because most likely something has failed in the feed back system and the computer goes into limp mode, locks timing and richen up the AFR so no power and bad MPG.
Guessing it would be the same on the v8 feed back truck too but not sure as I dont have one so have not followed.
Dave ----

 

Thanks for the ohms tip. I will give it a try.

Nobody likes limp mode!!

Ryan