I finally connected my Autometer water temp gauge the other day and I'm getting fluctuating readings. It will read about 150-160 degrees at idle, but if i press the throttle it raises up to about 180-190 degrees. Looks a bit like a tach as it raises and lowers instantly as your revving the engine.

Is there supposed to be some sort of resistor or something connected in line with this gauge to regulate the resistance maybe? A friend of mine suggested it could be an air bubble in the coolant system.

I have it connected the the sender below the oil filter.

 

electric gauge? its prolly a coolant bubble. plan b might be a bad ground, or maybe you picked a bad spot for power?

 

It's tapped into a 12v line under the steering wheel. Grounded to the chasis. Signal wire is coming from the sender under the oil filter.

On the FC chasis there are little resisters for the gauges to give them a better reading.

 

Sounds like air bubbles...
I just installed same gauge today and it did the same thing... burp the cooling system. It IS normal for the temp to go up under load.

 

II just figured if it was an air bubble the stock gauge would fluctuate too. I guess the Autometer is just extremely responsive.

 

The OEM temp sender is not calibrated to work with any of the aftermarket gauges, if that's what you're trying to do. Each brand of gauge has it's own ohm range. Please explain more on what you are trying to do.

 

stock gauge is rather well damped, you're talking about a needle width or two, stock gauge wont catch that

 

You've ruled out that the gauge is working fine and reading real fluctuations, right? If so you might check the chassis ground on the driver's side strut tower, my stock gauge was fluctuatingh like that and it turned out to be the chassis ground was just a little bit rusty.

 

It's grounded to the frame around the radio. I also have the oil pressure gauge from Autometer and it seems to be working just fine.

The temp gauge could be working perfectly as far as I know too. I was just making sure the fluctuations were normal while revving. The needle isn't wobbley while it fluctuates. It is very steady, but I was wondering if it could really shoot up 15 degrees just by revving it to 3-4000 RPM. I figured that the water pump accelerates while revving so that could cause it to change temperature...

 

You didn't explain what you're using for a sending unit for the AutoMeter gauge. I'm running both the Automete oil and temp guages, but with the approprite senders and haven't noticed the gauges being overly sensitive. Both my oil and temp gauges take thier respective readings from the oem locations but I took steps during the rebuild use the Autometer senders. I see no reason for your temp to be sensitive or jumping simply when reving between 3 and 4k.

 

I'm tapping into the sender under the oil filter. OEM.

 

Won't work nor read correctly. You need to use the Autometer sender to get an accurate reading from the Autometer gauge, they are a matched pair. When I installed the Autometer temp gauge to read from the oem position, I had to retap the threads while the engine was apart since the Autometer sender is much larger than the stock/oem sender. Autometer sender is 3/8" NPT iirc. Retapping gray cast iron is not an easy task.

It's the oem oil pressure sender that has the capacitor to condition and smooth out it's signal. You can cut the 'head' off of the 'mushroom' of the oil pressure sender, tap that remaining part with a flat bottomed 3/8" NPT tap and connect that to an Autometer mechanical oil pressure gauge. Capacitor is no longer needed.

 

for me i stayed away from those issues and went with mechanical oil pressure and water temp.

 

I was trying to resist but since you're having problems with the OEM spot, here's another solution (mine's mechanical, but should be fine for the electric autometer as well).

 

sorry ray, but egads that's hideous with that bright silver line dragging across the middle of the engine.

i realize the efficiency of going straight back to the firewall, but couldn't you have looped it down a bit deeper in the the engine bay to hide it, or is there some reason i'm not seeing to have it out on top like that?

 

I'm running the Racing Beat pedestal with Autometer sender for the oil pressure. It appears accurate.

I hope your line doesn't get eaten up by that rats nest Ray! It looks so complicated compared to mine.

 

I kinda like the looks of the mechanical line, compliments the rat's nest!

But yeah there are simpler ways to do it, just not ones as easy and inexpensive (the SunPro gauge was about $15).

Also being mechanical, the sunpro gauge is immune to electrical gremlins that tend to mess with electric gauges. In fact that's why I put it in originally, to get a second opinion on my original OEM gauge, which turned out to be wavering because of a chassis ground issue.

 

That's what I was wondering when you said you tapped in under the oil filter. You do know that adapter is for oil, not water, if it's the one that mounts under the oil filter and you can read either oil temp or oil pressure from that location. Oil pressure will easily vary from 15 to 60 psi between idle and 3k, temperature won't and I doubt that its an air bubble that's causing it.

 

Hmm...

I was told that it was a coolant temp sensor since the SA does not have an oil pressure gauge. I asked about tapping into the line on the tstat neck, and they said the other line gave a better reading... Eh...

So is my coolant gauge showing oil temp then? That explains the fluctuations...

 

The thing about the water temp readings being inaccurate at the tstat neck is urban myth, in my experience. I got all kinds of warnings about this (after I started the project), how it would read differently than the stock location and if the thermostat ever stuck I would burn up my motor.

Well, the tstat gauge tracks the stock gauge EXACTLY, except that it's temperature on the tstat gauge rises about 30 seconds after the stock gauge, as you would expect, since the tstate opens only after the block has heated up. They even track each other when I get small, just barely nocticable water temp changes at highway speeds or stuck in traffic. This it with that cheap bottom of the line SunPro gauge. As an extra bonus, the mechanical tstat gauge reads the engine temp when the engine is turned off, unlike the electric stock gauge.

The only real concern, which is highly unlikely if you have a recent thermostat, is thermostat failure (I haven't seen this in 40 years of driving!). In this case, if the tstat freezes closed, your engine might heat up too high before the thermal energy is transmitted to the tstat neck and detected on your aftermarket gauge.

Therefore I would recommend the tstat gauge as a backup gauge (mechanical preferred, since it works differently than the stock gauge) to provide a "second opinion" about your running temperature.

After all, nothing is more important than proper engine temps for a rotary! And having that second gauge really helps when diagnosing problems, especially if a squirrally stock gauage is involved, which often is the case.