1949 Oldsmobile 88 temp. gauge. HELP!!

[Guest 49oldsfan]

I have a 1949 Oldsmobile 88 with a 303 Rocket V8 engine. My temp. gauge has always worked great until yesterday. The gauge was reading temp. and then for some strange reason the indicator went all the way to cold and now it won't register at all. Can anyone tell me what the proper troubleshooting proceedure is for this? I have a 1949 shop manual for the car but it makes no mention of the temp gauge.

Thanks!!

[Guest simplyconnected]

Welcome, windsor. This is very common with capillary tube/bulb type gauges. The good part is, you can either fix it yourself, or have it done. Ether expands and contracts with temp changes, making your gauge deflect. Most commonly, the ether leaks out.

It's tricky, but several web sites explain how using ice, salt, a hefty solder iron, you can have a brand new tube and bulb.

http://www.ply33.com/Repair/tempgauge

http://www.fourfold.org/RoverWeb/mailinglist-archives/lro/2001/06/01/0004.html

http://www.mgaguru.com/mgtech/dash/dt101.htm

(Some of these sites are carbon copies of each other.) They like to buy a new unit, unsolder the bulb and tube from the gauge head, and solder it back on your gauge.

Hope this helps. Dave Dare

[Guest 49oldsfan]

My gauge is an electrical type. A wire runs from the ignition switch to one side of the temp gauge itself. Another wire runs from the temp. gauge to the device in the engine. With a mechanical type such as the one in my 1947 Chrysler it will register even if the ignition is off. Not so with the Olds. If the switch is off the gauge goes to cold as it should. Thank you for the web sites that you refered me to, but they are talking about the strictly mechanical type gauge. Does anyone know how to troubleshoot this electrical type with a meter? With a meter, if I read from the positive battery post to the wire attached to the device in the engine I read 6 volts( or thereabouts ) Or if I read continuity from ground to the wire attached to the device at the engine I have continunity with or without the wire connected to the device at the engine which tells me that that wire is grounded. Is it supposed to be grounded?, and what other troubleshooting proceedures are there for this problem? What are the principals that drive an electrical type gauge?

Thanks!!

[Guest simplyconnected]

Do you have a Shop Manual? It will show the whole schematic. There isn't much to it.

You're right, power comes from the ignition switch "RUN" position, and feeds the gauge. Then out of the gauge to an engine temperature sensor (they come in two flavors, one post or two post).

As your engine temp rises, the temperature sensor passes increasing amounts of current, causing the needle on your gauge to deflect. The meter has a spring which naturally pushes it to "COLD." Current works against that spring.

If you want to see the current, set your meter to "DC MILLIAMPS" and clip one lead to the sensor tip, and the other lead to the wire you took off (coming from the gauge). This will tell you how many milliamps are flowing through the circuit.

Remember, the sensor GROUNDS variable degrees of milliamps coming from the gauge, by changing resistance. Shorting 6vdc from your battery may fry the sensor, since it has no load (the gauge). 100% continuity shows the sensor is like a solid wire, passing current like a closed contact. That will cause your gauge show "HOT" all the time.

Put your meter on OHMS, and take the wire off of your sensor (lay it aside). Start your cold engine, and clip one meter lead to the sensor, and the other to a good engine ground. As the engine heats, you should see the resistance decrease. Again, it should start as a high number, and go down.

To test the gauge, use a wire to ground, solder it to a 1K ohm potentiometer, and tie the wire coming from the gauge to the wiper. Turn the key on, and slowly turn the pot. You should see the gauge move up and down as you slowly turn the pot. If the gauge shows "HOT" all the time, you may have a grounded wire. Pull on the gauge wire and check it to the engine compartment. Hope this helps. - Dave

[Guest 49oldsfan]

Dave, Thanks a million!

I do have a shop manual, and I tried to read the schematic but it's just my luck that that particular page and a few others have been damaged somewhat and made it impossible for me to read it. Your in depth expanation will now make it possible for me to pin-point the problem.

Again, thank you for taking the time to help with this.

Barron

[rocklin_ron]

I have a '49 Club Coupe on which I usually have to lightly tap the chrome frame on the gauge cluster just below the temp gauge to get it to come off C after the engine heats up. Then it records fine, but usually hangs up at C again every time I shut the engine off. I keep a half golf ball in the car to save my knuckles for this love tap, which everyone thinks is real funny.

I have a 1952 Motor's Repair Manual that has a pretty good section on the AC electric type temp gauge. Maybe this will add some to the detailed response you already have.

Check as follows:

1. Disconnect wire from binding post on engine unit and hold end of wire away from all metal.

2. Turn ignition switch on.

3. Check dash unit; the needle should point to the low mark C.

4. Touch the bare end of the wire to the engine block.

5. Check dash unit again; the needle should point to the high mark H.

6. If the dash unit does not indicate properly, first check the wire. If it is OK, replace the dash unit.

If the dash unit is OK per steps 3 and 5, this indicates reasonable performance of the dash unit and connecting wire. In this event, they have you check the engine unit by removing it from the block and operating it in a pail of hot water with a thermometer for reference. Be careful not to immerse the portion of the unit above the block threads as it may ruin the unit. Also, you must ground the unit to the block of the car at some point below these threads. If it does not read OK, replace the engine unit.