Greetings, Rik here, new to the forum.

I have a 1974 Chevy K-5 Blazer. I used it for many years while serving in the C.S.M.R. in Los Angeles, and custom-painted it woodland camo. Over time I got tired of constantly upgrading the pattern so left it just Army Green.

Anyway, I had the engine replaced some years ago and it's been running relatively good.

Within the past couple of years though, I would notice that the temp gauge was acting all 'twonky' working it's way straight up to 12 o'clock dead center and then w/o warning suddenly jump all the way over into the HOT zone and stay there.
Then just as fast, go back to dead center then back to Hot zone. and then back slightly off below that.

We haven't been able to figure out why it does this. I don't know if it's a real concerning issue and have many times had to drive this way for many many miles. Luckily nothing blew out.
About 3 weeks ago we swapped out the thermostat for a new one. The previous one didn't look bad at all, despite this temp gauge issue always happening.

For example, if I drive a 20 mile errand, before I get to the 3/4 mark of the journey, the temp gauge needle is all the way in the red and stays there.
I don't know why it does this so quickly.

Well, after installing the new thermostat, for the first week it was fine temp gauge never went past the center mark.
Week # 2, she began to go past that like about 15-20 minuted into the drive, even with the new thermostat installed.

It also takes some time for the upper hose to get warm while the bottom hose is hotter.
Yes, the radiator was replaced a few years ago but nothing troubling with that.
Also when the fan was re-installed, it sits slightly further away from the radiator too under the hood collar.

So, can anyone offer any possible solutions as to why this is happening with the temp gauge and what can be done to fix it?

Thanks,
Rik

 

The temperature sending unit varies the resistance to ground which the gauge uses to vary the needle position. If the wire to the sending unit is grounding out independent of the sending unit, it would cause the symptoms you are experiencing. Check the wiring at the sending unit (which should be located in the driver side cylinder head) and make sure that it is not resting against the exhaust manifold. Follow the wiring as far as you can to make sure that it is not grounding out anywhere. It is possible that the sending unit itself is faulty.

BTW, I moved your post out of the Gen Chat 'What have you gotten done on your blazer today?' post and into a thread of your own in the Full Size Tech section.

 

Yeah I noticed that Kyle... after clicking the link in my email a couple times & not being able to find the post, checking other emails etc lol.
I was going to say check the wiring as well. Something that drastic & fast usually equals electrical/grounding out. I also thought about the new thermostat & they can have a bad rep for not working properly right out of the box. But it DOES seem to go to the proper temp - when it's not dancing around like a blazer fuel guage at 1/4 tank.

 

Thank you both for your assistance I'll have a look into that.
-Rik

 

ive owned a few k5s and suburbans over the years and i think i only had one where the temp gauge actually worked properly or even worked at all. i run a aftermarket one in everyone i ever had. if you trace the wiring and everything still looks ok just go to autozone and buy one they are pretty easy to install