Temp light on at idle

[bobw]

What would cause the temp light to come on at idle but go out as soon as rpm's are increased? This happened driving to work this morning. I pulled over and the belt is on and all appears to be ok. Then the car wouldn't start for about 10 minutes, just cranked. But started right up after 10 minutes with the light still on.

Sent from my LG-K428 using Corvair Forum mobile app

[bobw]

It's a 1964 110 pg. Could it be a low pressure issue?

Sent from my LG-K428 using Corvair Forum mobile app

[bbodie52]

The TEMP/PRES warning light is shared by two engine sensor switches. With the key ON, power (12V DC) is continually fed to the warning bulb in the instrument panel. An electrical GROUND at either the oil pressure sensor switch (to the right of the generator) or the right cylinder head temperature switch will ground the bulb and cause it to illuminate. By default, the oil pressure switch is CLOSED (connected to GROUND) when there is no oil pressure (engine not running). This illuminates the TEMP/PRES bulb to test it when the key is turned ON, but before the engine has been started. The temperature sensor warning switch defaults to OPEN (NOT GROUNDED) when cold, and remains OPEN unless the cylinder head reaches an overheated temperature level.

You indicated that your TEMP/PRES warning bulb is glowing at engine idle, but that it goes out when engine speed increases above idle. The load from the torque converter drag on the engine with the Powerglide transmission naturally slows the Corvair engine idle speed somewhat, and a running engine's oil pressure is naturally at its lowest at idle. Does the TEMP/PRES light go out if you shift the transmission to NEUTRAL, and comes back on when the transmission is shifted to DRIVE? If so it would appear that the oil pressure is dipping below the pressure level threshold needed by the oil pressure switch to cause it to OPEN at the slowest engine idle speed (loaded by the transmission torque converter drag in DRIVE).

If this is a new condition that had not occurred before, and if the light goes out in NEUTRAL (with the engine not slowed by the transmission load), a slight reduction in engine idle speed that reduces the oil pressure below the oil pressure switch on/off threshold could be the cause. A slight change in engine ignition timing, for example, can cause a small reduction in engine idle speed, which could be just enough to cause a noticeable oil pressure reduction that — in your case — illuminates the warning light.

I'm assuming that your engine ignition system is in the standard configuration using ignition points, and has not been modified using a breakerless system such as that manufactured by Crane Cams or Pertronix.

The scenario I just described might match your situation, and might explain the change that is causing the warning light to come on. For example, normal ignition points wear in the distributor can change the gap in the points (DWELL) which can cause a change in the ignition timing that may slow the idle speed a little. Such a common occurrence could explain this noticeable change in your car's operation.

If this theory sounds like a reasonable explanation for the problem you are experiencing, you can possibly correct it by checking/adjusting the points, dwell, timing, and idle speed settings. An aging/defective oil pressure warning switch might also be an explanation. If none of this checks out, another cause may have to be found.

I'm not sure about the difficulty you had with restarting the warm engine, unless it might have been caused by a weak ignition system spark/dwell/timing issue. The points could be burned/worn/pitted, which could explain a slow idle and your difficulty with restarting the engine.

[b74eqcm]

Yes. Remember that the light comes on for both low oil pressure and high engine temperature. At idle, low oil pressure is more likely.

The way to be sure is to run it until the light comes on, and unplug the oil pressure switch to see if the light goes out.

Check your oil level, and while you have the dipstick out, sniff it to be sure it doesn't smell of gas. If it does, you need to change the oil right away, and also find our which carb is dumping fuel.

Assuming the above is ok, you'll need to temporarily install an oil pressure gauge where the low oil pressure switch is located to see what your actual oil pressure is. Then we can take it from there.

A couple of questions: Does it do this only when hot (or warmed up)?

Are you getting any lifter noise or other clattering from the engine when the light is on?

And any idea how many miles are on this engine since last rebuild?

[bobw]

This is the first time this has happened. I just converted to an alternator over the weekend, not sure if that has anything to do with it. There were no odd noises when the light came on but I have noticed occasional shuddering when turning off the car lately and the idle does seem a little low. I will check and adjust both the idle and timing tonight. The car has a pertronix 1 in it. Hopefully it's just a timing idle issue but at 2:30 am on the way to work I feared the worst.

Sent from my LG-K428 using Corvair Forum mobile app

[66vairguy]

If you installed an alternator, you must have replaced the mount (different then the generator). The mount contains the oil pressure switch. Did you move the switch from the generator mount, or install a new switch? It's not uncommon for the oil pressure switch to malfunction. You have to use the proper socket for installation or the switch can be damaged.

[bbodie52]

Now why didn't i think of that??? I thought of the alternator and possible related electrical issues, but I didn't even think of the necessary adaptor swap!

(Used adapters often are delivered with a used oil pressure switch still installed. Did you transfer your original switch, or did you use one that came with the new adapter?) A used switch from another source might have a slightly different pressure sensitivity, which could explain the new trouble you described at the start of this thread.

[azdave]

Those switches fail often. Luckily, they are cheap and usually can be found at local stores. They are easily damaged by people using big pliers to crank them in too tight. Go easy.

http://www.autozone.com/external-engine ... 828_0_8537

[bobw]

The new alternator bracket came with a new switch installed. Today I am picking up the oil pressure switch socket and I will put my old switch back in to see if that helps.

Sent from my LG-K428 using Corvair Forum mobile app

[bobw]

Thanks to everyone for the help and ideas. I replaced the oil pressure switch today and cured the dash light issue.

Sent from my LG-K428 using Corvair Forum mobile app

[bobw]

Looks like I was too quick to celebrate. Once the car warmed up the oil pressure light came on at idle again, I started losing power and couldn't get the car above 55mph. Then it started overheating and the noises started. Pulled over immediately and left the car on the side of the road until after work. Went back, it started right up but with bad tapping noises and a squeal that sounds like a bad bearing. Got the car towed home. I'll try pinpointing where the noise is coming from today.

Sent from my LG-K428 using Corvair Forum mobile app

[64powerglide]

In one of your late posts you said you would put your old switch in and see what happens. Well I thought your new switch was telling you something the old switch was not. Now the old switch that didn't send a signal & turn the light on seems to be the culprit that caused you some big problems.
Looks like everyone gave you some bad advice.

[bbodie52]

If the oil pressure switch is functioning, it will provide a GROUND to test the bulb when the key is turned on, but before the engine is started. When the engine is started, the oil pressure overrides the internal spring pressure in the switch to open the contact, and turn the warning light OFF. The warning light system only tells you whether or not oil pressure is present. A pressure gauge and sending unit would be needed to see if the oil pressure is adequate or low.

Did the oil pressure warning light go out above idle?

Oil pressure failure in a Corvair engine is somewhat uncommon, unless you develop a bad leak where all oil has been lost. The symptoms you described certainly sound ominous. Have you confirmed the oil level in the engine?

[b74eqcm]

In one of your late posts you said you would put your old switch in and see what happens. Well I thought your new switch was telling you something the old switch was not. Now the old switch that didn't send a signal & turn the light on seems to be the culprit that caused you some big problems.
Looks like everyone gave you some bad advice.

Actually, that's not true. After some simple checks, I recommended installing an oil pressure gauge (see above) to see what the oil pressure actually was. I don't think that ever happened. My simple diagnostic recommendation was overwhelmed by the longer, more exotic answers.

[64powerglide]

Sorry Jim I guess I should have said almost everyone. I should have posted what I thought at the time, it might have saved him some time & maybe money. I sure hope it isn't as bad as it sounds. I agree with the part about an oil pressure gauge. I'm hoping his fan bearing just went bad.