I can't figure out what is causing this, so I'll ask for ideas. I have a 35 with the red fluid filled temp gage. It's probably original because the fluid has been red since 1975 or longer. The car has gone through being re-restored in the last few years. It was converted to 12V neg gnd. The fluid was to the top of the glass when I unboxed it and finally got the fluid back down into the bulb by hanging it up for several months and tapping on it occasionally. After installation, the fluid was just barely visable at the bottom of the glass at room temperature. I am assuming this is correct. But we all know what 'assume' means. I have started the car only a few times, but have not run it long enough to get the temperature up at all. Here is the issue--When the engine is cranked over, not running yet, the red fluid goes all the way to the top of the glass. When you stop cranking, the fluid drops back down to the bottom of the glass. What could be causing this? My theory is a poor ground during cranking and somehow its using the temp cap tube as a path to ground getting it warm real quick and making the fluid level rise. I used teflon tape on the bulb, so it's not a solid ground to the block. I was thinking about running some extra grounds to the block, trans, frame, etc. Any thoughts on this?
Crazy water temp gage
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deuce lover
Well-known member
Having a good or bad ground has nothing to do with that type of gauge.It might need to be cycled a few time to work properly.
Kurt in NJ
Well-known member
Does the capillary tube get hot when you crank the engine? ---
Have you checked the voltage drop between the engine and battery to see if you have a grouind problem
you could loosen up the gauge and hold it away from any ground and prove if it is a problem
Teflon tape will get cut by the threads and make a ground there anyway
i have put the bulb in ice to get all the "red" to the bottom, and yes it is about at the bottom of the glass at room temp, holding the bulb in your warm hand for a while should just bring it up visible a little
Have you checked the voltage drop between the engine and battery to see if you have a grouind problem
you could loosen up the gauge and hold it away from any ground and prove if it is a problem
Teflon tape will get cut by the threads and make a ground there anyway
i have put the bulb in ice to get all the "red" to the bottom, and yes it is about at the bottom of the glass at room temp, holding the bulb in your warm hand for a while should just bring it up visible a little
I haven't checked the cap tube for heat yet or voltage drops. I just thought about the grounding deal while I was writing the post. I'll do that tomorrow. That might very well be the problem since I powdercoated just about everything that I could when it was apart. That stuff is tough, so it looks like I might have some scrapping ahead of me. I'm glad to hear that the fluid level at the bottom of the glass is correct. Thanks.
While on the subject of voltage drops, I did find something odd a few weeks ago. I had a slight current draw at the battery with everything off - about 7-10 milliamps. Nothing major, but enough to pull the battery down if it sits a while. After several days of checking lights, connections, wires, etc. , I found the toggle switch that my dad had put on for the electric fuel pump back in the 70's had a slight bit of continunity across the terminals when in the open position. I figured it was old and dirty inside. I replaced it and the milliamp draw went away. Lesson learned. Just because a switch 'clicks', doesn't mean it is fully on or off.
While on the subject of voltage drops, I did find something odd a few weeks ago. I had a slight current draw at the battery with everything off - about 7-10 milliamps. Nothing major, but enough to pull the battery down if it sits a while. After several days of checking lights, connections, wires, etc. , I found the toggle switch that my dad had put on for the electric fuel pump back in the 70's had a slight bit of continunity across the terminals when in the open position. I figured it was old and dirty inside. I replaced it and the milliamp draw went away. Lesson learned. Just because a switch 'clicks', doesn't mean it is fully on or off.
ford38v8
Well-known member
Your gueseplanation is interesting, but I agree with deucelover. If the bubbles don't work themselves out in the first 500 miles, dismount the unit and play with it some more. Get inventive with your methods and it'll cooperate finally.
Before installation, when you think you may have it solved, check it in boiling water against the etched calibration mark on the glass. if it doesn't match that mark, you still have bubbles. When you've got it right, install the glass with the calibration mark lined up at the indicated 212º mark.
OLD...BILL
Well-known member
You may be using the capillary tube and cable as a ground between the engine and the dash ( body ) ... more grounds the better, yes, but not this way..... OR ... the capillary tube is seeing compression as you crank the engine ?? as a way to check my ? "THEORY" ? drain the water out and pull all the spark plugs, and give the engine a test crank, and see what the red stuff dose ?? if.. a big if.. the temp gauge is still, I hate to say it.. but you may have a blown head gasket ?? ....OLD.....BILL
I had to postpone the temp gage project. I got an order for more car show awards. They keep adding classes. It's up to 49 awards now.
I did start it up and found another symptom that points to the grounding might being the problem. It was idling and I grabbed the carb throttle rod - the one bolted to the firewall. It was noticebly warm. Not hot, but warmer than the other rods. It was could have been acting a ground path also. I haven't seen any bubbles in the radiator and the head gaskets have no miles on them since regasketing the engine. If it a head gasket, then I am the guilty one. I'll go the grounding route first and then if it still acts up, I'll ice pack the the bulb and heat it up several times. But first, I have to finsh up the awards. I'll post what I find.
I did start it up and found another symptom that points to the grounding might being the problem. It was idling and I grabbed the carb throttle rod - the one bolted to the firewall. It was noticebly warm. Not hot, but warmer than the other rods. It was could have been acting a ground path also. I haven't seen any bubbles in the radiator and the head gaskets have no miles on them since regasketing the engine. If it a head gasket, then I am the guilty one. I'll go the grounding route first and then if it still acts up, I'll ice pack the the bulb and heat it up several times. But first, I have to finsh up the awards. I'll post what I find.
Success!! I started with the easiest part first. I added some grounds between the dash and body, body to frame, and frame to engine. This time I made sure to scrape all the paint and powder coating off under the connections. The battery ground was left connected to the u-joint cover as it should be. I cranked it over -- no red fluid up to the top in the temp gage. It warmed up a little and the fluid started coming up. The throttle rod was also nice and cool. I didn't run it long because it'd inside my shop with the doors closed (A/C on). So insufficient grounding was the problem. I'll wait until it cools off tonight to drive it on its maiden voyage. It's 102 right now and I don't have the top installed yet. Tough on an old bald head. Thanks for all the suggestons.
Dick Webber
Senior Member
I had a 54 Corvette 6 with a bulb heat gauge which acted the same way right after an engine change. Grounding thru the gauge