75 dash guages
Thread Starter
Racer
Joined: Sep 2016
Posts: 312
Likes: 12
From: Tipton In.
75 dash guages
I'm in the process of redoing a 75 that has been sitting in a shed for 26 years. I have gotten it running but what I'm running into now is that the oil pressure and temperature guages are not reading right. I have a mechanical water gauge hooked up to a fitting in the thermostat housing and the dash gauge installed in the original place in the side of the head. What is happening is that the dash gauge is reading hot while the mechanical gauge isn't. Also the oil pressure gauge in the dash is pegged while the mechanical is reading 70 lbs. The fuel gauge also was giving me problems but I ran a new ground wire at the tank and cured it. Am I also having ground problems with the other 2 gauges or is it something else. This is a newly rebuilt engine that I just finished installing. Thanks Larry
Last edited by truckerlary; Oct 16, 2016 at 08:38 PM.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Hey Larry, this sticky thread from Willcox has info and videos for troubleshooting the gauges as well as many other problems.
https://www.corvetteforum.com/forums...post1581495000
https://www.corvetteforum.com/forums...post1581495000
Safety Car
Joined: Mar 2003
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From: Indianapolis IN
Finalist 2020 C4 of the Year - Unmodified
C4 of Year Finalist (stock) 2019
Are the oil pressure and temp senders new or did you re-use the originals? I always replace all senders on a rebuild, but not everyone does...
As for the grounds, check them ALL...especially those for the gauges. These cars are loaded with ground wires (for obvious reasons) and you can have an open or high resistance ground that will give you all sorts of weird problems. Grab a Fluke, a thermos of coffee, the wiring diagrams, and start checking.
As for the grounds, check them ALL...especially those for the gauges. These cars are loaded with ground wires (for obvious reasons) and you can have an open or high resistance ground that will give you all sorts of weird problems. Grab a Fluke, a thermos of coffee, the wiring diagrams, and start checking.
Last edited by Red86Z51; Oct 17, 2016 at 07:50 AM.
Thread Starter
Racer
Joined: Sep 2016
Posts: 312
Likes: 12
From: Tipton In.
gauges
Are the oil pressure and temp senders new or did you re-use the originals? I always replace all senders on a rebuild, but not everyone does...
As for the grounds, check them ALL...especially those for the gauges. These cars are loaded with ground wires (for obvious reasons) and you can have an open or high resistance ground that will give you all sorts of weird problems. Grab a Fluke, a thermos of coffee, the wiring diagrams, and start checking.
As for the grounds, check them ALL...especially those for the gauges. These cars are loaded with ground wires (for obvious reasons) and you can have an open or high resistance ground that will give you all sorts of weird problems. Grab a Fluke, a thermos of coffee, the wiring diagrams, and start checking.
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From: Jeffersonville Indiana 812-288-7103
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I'm in the process of redoing a 75 that has been sitting in a shed for 26 years. I have gotten it running but what I'm running into now is that the oil pressure and temperature guages are not reading right. I have a mechanical water gauge hooked up to a fitting in the thermostat housing and the dash gauge installed in the original place in the side of the head. What is happening is that the dash gauge is reading hot while the mechanical gauge isn't. Also the oil pressure gauge in the dash is pegged while the mechanical is reading 70 lbs. The fuel gauge also was giving me problems but I ran a new ground wire at the tank and cured it. Am I also having ground problems with the other 2 gauges or is it something else. This is a newly rebuilt engine that I just finished installing. Thanks Larry
So there are things your non working gauges can tell you.. and I'll give this a quick go..
A gauge that is missing ohms input (wire off the sender or non working sender) will always read to what you want best.. An example..
A fuel gauge that is missing ohms input will read full, an oil pressure gauge that is missing ohms input will peg oil pressure and a temperature gauge missing ohms input will always read cold..
It's just the opposite for a ground out gauge which will read empty, 0 and hot respectively.
So.. lets start by what each gauge is reading..
The temperature gauge is reading hot? How hot? This issue could be a defective replacement sending unit (which they are all junk) and can be corrected by installing an adjustable resistor on the back of the dash unit... But questions impede my judgement as t what the issue is without knowing a few things.. Does the temperature gauge read hot all the time or does it move with the engine heat build up and just read hotter than what you think the temperature is?
The oil pressure gauge is pegged.. you are missing ohms input.. Go to the sender and ground out the wire and see if the reading goes to zero... if it does replace the sender if it doesn't then you have an issue in the wire between the sender and the dash unit.
Go to my page and watch the videos..
They will help you figure this out..The only difference between a fuel gauge and a oil pressure gauge is the resistance oil inside. An oil pressure gauge has less resistance than a fuel gauge (it's more responsive) but it works on the exact same principle... 0 - 90 ohms...
So watch this video on a fuel gauge and just pretend it say's oil pressure.
1968-1976 Fuel Gauge Testing. What can your non working gauge tell you.. Plenty.
If you have a bogus sender for the temperature gauge, here is the fix.. but it will only work with an original gauge.. it will not work with the imported china gauges since the resistance is on the inside of the gauge and not in the form of a resistor outside the gauge like the OEM gauges were made.
68-76
Willcox
