Mechanical Temp Gauge Problem ? - Team Camaro Tech
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post #1 of 12 (permalink) Old Apr 4th, 02, 02:05 PM Thread Starter
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Has anyone ever had a mechanical temp gauge go bad and give erratic high readings ? I had been getting erratic high temp readings (230-260) which would then drop quickly to 160-180, and I thought my thermostat which was fairly new was sticking. So, I replaced it, and now my gauge is still doing the same thing. This is the second mechanical gauge I've had to buy; when the first one went bad, it only gave very low readings. If this one is bad, I think I'm ready to go with an electrical gauge. The engine doesn't seem to be running hot. Any one else had a problem like this with a mechanical temp gauge ?
Thanks, Ron.
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post #2 of 12 (permalink) Old Apr 4th, 02, 03:21 PM
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Nope. I've had it happen with electrical gauge. Wire grounding out. Could a hot wire possibly be touching it? Just throwing something out there.

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post #3 of 12 (permalink) Old Apr 4th, 02, 06:42 PM
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call the manufacturer of the gauge and ask them. did you check the tubing to see if it got pinched or anything like that?

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post #4 of 12 (permalink) Old Apr 5th, 02, 05:43 AM
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I run a mechanical gauge in my 68, 350,
It runs a high temperature, during the summer months, I worry about the Temp all the time,
The way you explain that the gauge drops to 160 -180 suddenly, is when the thermostat opens and allows the coolant to flow through the radiator, If this has happened with two different thermostats, and the gauge reacts the same then I would assume that the engine is fine and look at your gauge.
In my 68 I run the mechanical gauge in the water plug right under the thermostat housing, The tube runs along the top of the intake manifold, under the distributor and through the firewall, It is this routing I believe that causes the gauge in my car to run such a high temp, 220 -230, No thermostat, just a restrictor ring, I also use the original temp light plugged into the water jacket between # 1 & 3 plugs, Funny how the gauge reads so high and the light does not flicker or come on, I have concluded that the temp reading of the gauge is high but the actual engine temp runs 20 -30 degrees less than the gauge reading, It could be possible that the tube is picking up heat from the manifold, near the carb and affecting the gauge reading.
I think that if I were to change the location and routing of the tube away from the engine then the gauge may read accurate.
What water jacket plug are you useing??
Where is the tube routed??
Can any body else offer comments???
Rob
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post #5 of 12 (permalink) Old Apr 5th, 02, 08:51 AM
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Hi Rob, I run my mechanical temp about the same place you do. Except I run it along the edge of the valve cover, to the front of the aluminum manifold. My 327 is punched 60 over, and I never run over 185 in the summer. It usually runs around 170-180 depending on how tight I spin it.
There seems to be a long delay though on starting it and waiting to get a temp reading. Once it hits 110, it will jump up to 160, and then slowly climb up to operating temp.
But it has always been consistent.
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post #6 of 12 (permalink) Old Apr 5th, 02, 09:16 AM
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First find someone with an IR gun and verify the temps for accuracy and peace of mind. then look for a flakey ground. The other thing that comes to mind is did you put teflon tape or anything around the threads in the sender? Check the directions as each manufacture is different and some say it's needed some warn not to use it.

Let us know what you find.

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post #7 of 12 (permalink) Old Apr 6th, 02, 03:32 AM Thread Starter
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Thanks to everyone who replied ! I have the sender for the temp gauge installed at the front LH corner of the intake. The tubing runs down along the edge where the intake and the valve cover meet, then straight through the firewall (I used a rubber grommet). I can't remember if I put teflon on the threads or not; I've had this gauge for six years (its been in 2 different engines) and it has worked fine until now. I have a brass bushing in the intake, and the sender threads into it. I do remember that there was a long "bulb" on the end that sticks into the coolant passage. I would like to put a sender in the block where Rob.Canada put his, and hook up the "temp" light. We have a IR heat gun where I work, if I can get access to it, I'll check it with it.

Another thing that I was thinking about, is that I recently re-plumbed my coolant that runs from the nipple on top of the water pump to the heater core. I re-routed this flow through the intake (I have a vortec heads which have no center coolant passage). The Performer RPM intake I have has threaded "bosses" on each side of the carb with a passage underneath to allow you to do this. The reason I did was because it was idling poorly in cool weather, it did help that problem. I used brass fittings and elbows so the hoses would not be kinked.

It hasn't been long since I did the re-routing, and I really don't know if that's when the temp gauge problem started. I'm going to reverse the coolant re-route today, and see if that changes anything.

I would just go buy a new guage, but since they're not exactly cheap ($40-$50), I'm trying to avoid it. The thing reads real close to 180* for long periods of time & then goes haywire ! If it wasn't for the sometimes steady readings I'd say it was bad for sure. Like I said before, when the first one went bad, it gave a very low steady reading.

I was also thinking, could this be a water pump problem ? I've had the same water pump on the car since I've owned it (12 yrs / 3 engines).

Thanks for everone's help, Ron.

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post #8 of 12 (permalink) Old Apr 6th, 02, 05:41 AM
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DJD, Teflon tape should not cause any problems with a mechanical gauge, but would certainly be a problem with an electric gauge that requires a good ground at the sender,
Steve thanks for your reply, Something that I forgot to mention is that my 68 is equipped with AC and has that big air flow restrictor in front of the radiator, could also cause a higher temperature,
Ron I can't see the water pump being a problem as it does not actual "PUMP" water but just moves it through the engine, Check the coolant flow by looking in the rad when the thermostat opens you should see an increase in the flow of the coolant.
You could try moving the gauge and see if the reading changes, let us know what you find Thanks Rob.
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post #9 of 12 (permalink) Old Apr 7th, 02, 03:41 PM Thread Starter
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Well, I think I've got a bad water pump. I reversed the coolant routing changes I made, running the heater core hose to the nipple on the water pump, as it was originally. The temp gauge then stayed between 180* and 200*. I think that the extra hose and coolant passage must have slowed down an already weak flow.

I think the coolant flow was weak because the coolant would just barely dribble out of the radiator tubes. I remember in the past that it would actually squirt out of the tubes when the level was low, and you could see a swirl when you took the cap off if it was full. I'm sure the radiator isn't stopped up either, because I put it on new, and I change the coolant very often.

I also noticed that the water pump pulley looked wobbley, and it sounded like it was making a rattling noise. I cut the engine off, and loosened the belt. There is a little sideways play in the water pump shaft; it's not leaking any coolant out of the weep hole though.

I'm glad it's the water pump, and not the gauge. I've been wanting to replace the old flakey chrome steel one with a nice aluminum pump for a while anyway ! I know this pump is over 12 years old, and it made many visits to 6 & 7K RPM on the engine that I had before the one I currently have.

Anybody got a comment, or a suggestion on an aluminum water pump ? Thanks, Ron.
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post #10 of 12 (permalink) Old Apr 9th, 02, 08:52 AM Thread Starter
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I just ordered an edelbrock long style aluminum water pump; I hope that takes care of my problem. They're a bit pricey at $150.00 !
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post #11 of 12 (permalink) Old Apr 10th, 02, 09:00 AM
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If it helps, I had the exact same symptoms you described after installing a new GM crate motor. I am not running a heater so I blocked off the fittings at the intake and water pump. The problem...the new GM blocks do not have a water by-pass in the block. I installed a bypass from pump to intake and it solved the sudden 220 degree readings I got when the thermostat opened. If your water pump doesn't solve the problem, and you have a new GM block, check your plumbing. Maybe this will help others in the future.

[This message has been edited by Mike67RS (edited 04-10-2002).]
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post #12 of 12 (permalink) Old Apr 10th, 02, 10:25 AM Thread Starter
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Mike,
I have a '96 Vortec 350 truck engine. I figured out that it would have a by-pass, since the block and the head have the by-pass passage, but there doesn't seem to be a hole in the head gasket, and I didn't want to change them. I've got a high flow therostat that came with about a 1/16" hole in the housing which should be enough to at least move the coolant through the block as it is warming up before the thermostat opens. I've had this engine for about 3 years, and the temps have been steady until lately. Thanks for your reply, Ron.
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