oil-pressure light glowing some...

[Formerly Steve Wilkinson]

Car is an '83 SC, engine totally rebuilt and upgraded 1,500 miles ago. Oil pressure is a solid one bar per 1,000 rpm, unfluctuating, with the engine good and hot. Temp runs a little below 210 F. on a 90-degree day on the road--which we suddenly have here in New York--and 250 at the track, and oil quantity is if anything a bit high. (Doesn't really matter on this engine since the breather goes straight from the tank to the crankcase, since I now have PMOs rather than CIS.) Yet after about an hour of driving, the oil-pressure warning light slowly begins to glow more and more until it's nearly full on, then eventually goes away, all other indications being totally no-problem. Obviously a sensor problem, but I'm curious: has anybody else ever seen this? Without having cracked the books, I'm assuming there are two sensors--one for the gauge and one for the warning light--but I don't at this point remember. Just back from the Imola GP--got out of Italy to France before the strike--so I'm still fuzzy.

Stephan

[Otto]

If the oil pressure measured with the guage is correct, then you should look at the idiot light switch or the circuitry associated with the switch. If you know how to use an ohm meter, disconnect the wire off the back of the idiot light bulb and measure the resistance(OHMS) in the wire between the light bulb and the connection on the idiot light sender in the engine compartment. Old wires gain resistance with temperature increase, a common problem we have noticed over the years. If the resistance in the wire that goes between the bulb and the sender is greater than zero, then that is the problem. If the resistance is zero, then you must have one of those elusive homotrons in your car.

[Kevin G.]

Stephan:

I'm curious, how did you route your breather hose directly to the case? I may wish to do the same and replace the airbox with Watershields.

Thanks,

Kevin

[Formerly Steve Wilkinson]

How? I, uh, routed it directly to the case. What can I say? The hose--it's an OEM part, a rubber hose covered with interwoven cloth, sized and intended to do exactly this--goes from the pipe on the side of the oil tank to the oval unit atop the crankcase at the forward (toward the firewall) end of the engine. Passes forward of the righthand set of PMO carbs. Same as on a lot of stock, earl(ier) 911s. Creates a closed-loop system. I too have watershields on the carbs, and they do have small holes on the side of each metal cover, which I've always assumed was for some kind of breather system. I don't use the holes.

Stephan

[Stinky 911T]

Stephan - Isn't the purpose of the hoses you described to ventilate the crankcase and the oil tank? It seems to me that both need to be vented to the atmosphere (eventually) to equalize the pressure inside with the outside. Won't a "closed system" as you described it build up pressure as the system heats up and the oil expands until the excess pressure finds another path to the atmosphere?

With the original equipment, I believe that the hoses connect to the air cleaner so that any combustion by-products that leak past the rings into the crankcase get sucked into the intake and burned in the engine. If you want to duplicate the original setup with the K&N's, shouldn't the hoses connect to the holes provided?

[Superman]

Yes, ultimately the pressure needs to go somewhere. Emissions regulations won't permit venting to the atmosphere like in the olden days. So, it is vented to the air box where those oil fumes can go through the hot part of the engine.

The oil pressure switch (that feeds the idiot light) is on the breather cover at the top of the back of the engine (near the tranny/firewall).

[Formerly Steve Wilkinson]

The oil tank vents to the atmosphere through a small K&N air/oil filter that comes with the PMO carb kit.

Stephan