Technical Lets talk temp gauge theory

So, I was on the way home form the SWMO HRH a month or so ago and 650 miles into the trip, the temp gauge started climbing. It was a rapid increase to 250 degrees. I immediately hit the first exit and checked the head with my hand and it was warm but not super hot.

Anyway, exited off the highway and limped it home on Rt 66 at about 40 mph. As long as I kept it under 40 it was happy. Any thing above that and it would creep upwards. Pull over and it would immediately drop back to normal. I used my infrared temp gun and it shows 185 on the radiator water necks, heads and water pump.

I suspected the temp sender, so today I changed it. No change. I can only assume it is the gauge, which is only a few months old. I am afraid I have to buy it in a kit and not separately.

I release the resistance is measured across the sender, but component makes the gauge act up? It's just reads voltage across 2 poles correct?

So any suggestions?

 

I have no faith in electric temperature gauges. Start with a mechanical gauge and trouble shoot from there.

 

Working as a mechanic I always kept a mechanical gauge in my tool box, or on my service truck, and that is one of the first things I'd do to confirm if I had an actual problem or not, temporarily swap out the gauge with the mechanical one and test it to see if the mechanical gauge also showed it running hot. If not, I knew the problem was with the gauge, not the cooling system.

 

It's a variable ground. Full ground pegs the gauge, fully open circuit shows no gauge movement at all, all points in between are equal to the variable resistance.

 

If it's a flathead Ford, your temp senders could be shorted or bad

 

Got a few more details? How many wires are connected to the gauge? Do you have a ground strap between the engine and the frame AND body? What's the ohms range of the gauge, i.e. does it read 10-250 ohms cold-to-hot or the other way around? (note these values are just an example; different brands can use different values).

Electric temp gauges have been standard equipment on almost all cars since the mid 50s, they've proven to be accurate and reliable if installed right and of good quality.

 

So the gauge is part of a "kit"? .......and it's only a couple of months old? There should be some sort of warranty. It would be very bad karma for the seller if there isn't. Do contact the seller and give him a chance to make things right. (I understand that we can buy stuff for our projects months, sometime years before we install them. This won't help your case.) If you hit a dead end and it's been less than a year then you can flex your credit card muscles and have the credit card co make the money part of the deal slip back in your pockets.

But primarily you just want to establish that you don't in fact have an overheating issue and you have a working gauge. Start with the simple stuff first. Check the connections, the ground(s) in particular, then the sender (don't use teflon tape, etc.), then beg or barrow a known, working gauge to cross check, and so on up the ladder. 90% of the time it's one of the simple things.

 

Good info^^^^^

 

Mark, I can't find anyone that has a spring. Where did you find yours?

I bought a kit from Speedy Bill. It's been a few years, but only installed for a few months. It was the only kit I have ever found that would fit a 36 Ford pickup speedo hole without modifying, so thats why I bought it.

Guys, I am a ground freak. Every gauge gets its own ground. I have a remote post that grounds the battery to the frame, the gauges to the battery, and the battery to the starter. All separate.

It's not a flathead. It's just a common run of the mill sbc crate engine. It has the biggest Walker radiator, cooling components electric fan with shroud, flow kooler high flow water pump, high flow thermostat.

 

Read:

http://www.madelectrical.com/workshop/water-temp-gauge.shtml

 

er just get THIS type---->
.

 

like this^^^^^

and or just STAY Mechanical...

 

I believe it's accurate or at least it's working. I can watch it fluctuate when the thermostat open. It follows the full range of motion. I'm starting to think Mark may be on to something. As soon as I drop down in speed, it drops back to normal within a minute or so. The reason I am thinking he may be right is that the lower hose is molded and I was thinking when I installed it, that it was a little flatter than I liked. With the high volume pump, it may be collapsing. It's cheap enough to try. Can't hurt. I ordered the spring, should be here Tuesday.

 

I'm sure you know this but I'm old and like to repeat things ,but I get a reading 11 degrees higher when I use the cyl head for the temp sensor ,instead of the intake manifold.

 

install a sbc your troubles should fade away

 

Reading is an amazing tool. You should try it.

 

I use the head port for my electric fan sensor.

 

Just showed up yesterday. I've been down with the crud, maybe this week I can get back on it.

 

To add to thing's closing off circulation like a missing spring on a lower hose. I had an issue much like that after installing a water pump that had a higher volume flow than stock. It would close my thermostat at high rpm's and the only way to get things flowing again was to stop the engine and let the pressure equalize.

 

no offense But ... those hoses are about as bad as a flat one , they cause lots of internal restriction and cavitation from the ribbing . if not internal springs then do what we do on industrial and big trucks, use solid metallic tubing and short rubber sections to connect it to the parts ( speedway sells it and its correct as flatheads used them ) the metal also conducts heat and helps cool the coolant .

 

I run 2 temp gauges in my SBC crate engine. One directly in the intake manifold and the other mounted in my dash. Perhaps you could use 2 as I have done? This would certainly give you an accurate reading and you can use the 2 gauges as a "checks and balances" with your temp readings. I know this doesn't solve your issue, but it sounds like you'll have it resolved once you can install your new parts. Hope you feel better soon.



And another mechanical temp gauge in the dash.

 

Thanks. I was looking for a direct mount gauge the other day. That one would work just right I think.

 

I purchased that intake temp gauge directly from Moon Equipment in California. They were great to work with over the phone.
They are available in a few different face sizes, mine is the larger face. I really like it as it's nice to have.

 

I think that's what I will do. I'll have it drained down anyway, might as well mount the gauge at the same time.

 

You said crate engine is it stock? If it has Vortec heads on a pre Vortec block you need a circulation hose or drill the head. Vortec blocks don't have that extra port where the water pump bolts on that let's water circulate in the block when the thermostat is closed.

 

^^^^^ Yeah, Chris....we've all been sitting on the edge of our computer chairs waiting to see what happened!