C1 Temp Gauge Reading vs. Reality
I spent a long time last night reading a ton of forum threads about overheating and the issue of accurate gauge readings vs. actual engine/coolant temp. I've been nervously watching my '58's temp gauge needle climb in slow traffic and make seemingly improbable shifts, so I decided to ask a C5 buddy of mine to help me verify what's happening. He's got this expensive, highly accurate, digital temp probe that he uses to, among other things, check his tire temps. He's a racer. Anyway, I stopped at his house on my way back from a cruise and sat idling in his driveway while I went to find him. He got out his probe and told me some war stories about how accurate it is. Meanwhile, my '58 (270 Duntov) sat idling for about five minutes. We popped the hood and I asked him to take readings directly on the thermostat housing, at the base of the temp sending unit, and on the top rad hose just above the thermostat housing. All three readings were 167 degrees. My temp gauge was halfway between 180 (12 o'clock) and 240 (about 2 o'clock). My ballpark guess is that this indicated ~210 degrees. So, you can see the difference between the gauge reading and the actual temp readings. I had assumed that I had a 180-degree thermostat, but now I'm wondering if it's a 160. What do you guys think? Obviously, the problem is either the gauge or (more likely) the sending unit. Should I fault-isolate this or just leave well enough alone? I'm running a stock rad with a six-blade fan spacered out closer to the rad. I've driven this car over 6,000 miles in two years and have had no cooling issues other than this squirrely gauge. Oh, and while I have you all on the line, here's a related question. I have no expansion tank (or "supply tank," as it's called in the repair manual). It appears as though the hose that would have connected to the expansion tank just runs down the side of the rad and ends just above the rad shroud mounting flange. I see no evidence of puking. Any negative consequences for the lack of an expansion tank? Thanks very much, guys. Dave
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Last edited by David B.; November 11, 2012, 08:16 PM. -
Re: C1 Temp Gauge Reading vs. Reality
The problem is typically the sending unit, not the gauge, but it could be the gauge. For my 1960, I went to the local parts store and asked them to bring out all of the sending units they had in stock that would fit my car. I used a multi-meter to test the resistance of each unit until I found one that matched the correct resistance at 72 degrees F. i don't remember now what that number was supposed to be. When I take the temp on my thermostat housing, it matches the temp gauge fairly close. I am running a 160 degree thermostat. -
Re: C1 Temp Gauge Reading vs. Reality
I do not believe that an "expansion tank" was used on 1958 Covettes. These were used on the aluminum radiators in 60 thru 62. The brass radiator was used in 1958 thru 1960(230Hp cars). That is my understanding anyway.Comment
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Re: C1 Temp Gauge Reading vs. Reality
I appreciate that comment, Philip. The pictures and text in my '58 Corvette maintenance manual show and mention the tank, but the engine pictured is a 327, which is odd, I think, in a '58 manual. When I searched the Web for a '58 expansion tank, I couldn't find one at any of the usual suspects. Do any of you NCRS experts know whether or not '58s had a supply tank? I think Philip may be correct. DaveComment
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Re: C1 Temp Gauge Reading vs. Reality
You didn't ask this--but my understanding is that the fan is most effective pulling air though the radiator when it is aligned with the edge of the shroud. Spacing it closer to the radiator actually makes it less effective.Comment
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Re: C1 Temp Gauge Reading vs. Reality
According to the judging guide (58-60) Chassis section 26 page 74. The 58 would have had a copper radiator with a conventional tank. The aluminum expansion tank type was not available until 1960 and only high horsepower engines. They state even some of the 1960 High horsepower engines may have copper radiators installed. I pretty sure my 1958 did not have an expansion tank. From what I can gather your car should not have an aluminum type radiator as standard or optional equipment in 1958.
PhilComment
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Re: C1 Temp Gauge Reading vs. Reality
Thanks for that, Phil. My new problem is that now my rad cap is stuck. I think the cap's rubber gasket is bonded at the sealing point. I can turn the cap and get the notches to align for release, but it won't pull off. I don't want to pry it for fear of damaging the filler neck. The rad is OEM copper, as you note. Ever had this problem? Any tips on how to unstick that gasket without ruining the cap/rad? Thanks. DaveComment
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Re: C1 Temp Gauge Reading vs. Reality
Sometimes it gets stuck on the little tab stop on the radiator neck, pushing down on the cap and turning should release the cap. Somtimes the catch on the cap is turned up a little to make the seal tight. That is what I have seen in the past anyway. Mine catches sometimes, it is a reproduction cap and well lets say the fit is not all that great.
PhilComment
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Re: C1 Temp Gauge Reading vs. Reality
Mike
I was always under the same assumption as you about the location of the fan to the shroud. In trying to find a solution to an overheating problem on a friends car, we talked to a few of the leading aftermarket fan companies and there take is the fan blade should be half way into the should edge for max cooling, too far in or too far out results in less cooling. Just passing on what they said.
TerryComment
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Re: C1 Temp Gauge Reading vs. Reality
Terry,
i think we're saying the same thing. The center of the fan blade, fore-aft, should be aligned with the trailing (aft) edge of the shroud.Comment
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Re: C1 Temp Gauge Reading vs. Reality
Mike
Sorry Mike I thought you meant the front of the fan blade was in line with back of shroud.
TerryComment
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