OK. 1968 Valiant. Recent work includes: two barrel upgrade, distributor re-curve, HEI, all new drum brakes, headers, new exhaust, upgraded radiator, larger unit for A/C someday, belts, water pump, and performance fan. Runs very well. Quiet, smooth, cranks immediately. Only issue: When car runs for close to 30 mins straight, when at idle, in gear, the oil light comes on. Not around town driving, only when running for a little longer. And only when in gear, when in park light goes off?? oil level is good, Mobil one. Is it a pressure issue? Thanks. Again...new guy learning. Thanks.

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1968 Plymouth Valiant-225-more door.

Welcome to the Forum.

From reading your post, I would surmise a few possibilities.

The engine is older right, high mileage? You may be seeing a slight drop in pressure as the light is indicating. When in gear the engine is running more slowly, let's say you're idling at 600 rpm ish. When you put in in park, the rpm's increase a bit and your pressure goes up past the threshold of the sending unit's ability to read pressure and the light goes off. That is, your sending unit is working fine, and you just have low pressure at long low rpm idle situations.

Could be you're sending unit is going bad, can't detect pressure as well at low rpms. One way to check this hypothesis is to put in a new pressure sending unit at next oil change. If it still has the symptom, then it's more likely the first guess.

Either way it doesn't sound like you have anything to worry about, if the light only comes on at idle after 30 minutes in a traffic jam, I'd say you're safe as long as you don't run it too long with the light on. Slant sixes are generally bullet proof.

brian

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https://tinyurl.com/yynpj4v2

Full Disclosure of SL6 Blasphemy: when I was a kid we drained the oil from a slant and ran it at full throttle to see just how long it would hold up. It ran for several minutes at full throttle before slowly seizing up due to heat load/lack of lube. This was not a scientific test, no controls, just kids screwing around before installing a 340 cu. in It was fun at the time, but now that I've seen the light, I must repent. brian

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https://tinyurl.com/yynpj4v2

She is original motor..just turned 80k. I will replace sending unit just because..I hate idiot lights. I am also running Florida heat and humidity...with no A/C. It's really not too bad. Just excited by how well the work came out..fun to drive. Want to be sure she's right. Thank you for the insight.

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1968 Plymouth Valiant-225-more door.

Install a Oil Pressure Gauge, if you haven't already! (Preferably Mechanical)
Change the pressure switch at the same time with a "T" to have both.

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1964 Dart GT

I'm going to pressure gauge eventually, but not mechanical. I installed a VDO gauge in a factory cluster. Check it out:

http://s785.photobucket.com/user/67dart ... ort=3&o=66

I've since painted the needles to match, but I haven't installed it yet. I'm waiting for other projects to finish, but it's on my list.

brian

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https://tinyurl.com/yynpj4v2

Service the oil pressure relief valve to make sure it's doing its job, as described in these two threads: thread 1, thread 2.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

The Mobil1 synthetic is going to do a good job of protecting the engine, and with this happening when hot, your pressure should not be too awfully low. I could tell you a long story about that but it really does offer a large degree of protection. BTW, what weight of Mobil1 are you using?

I'd certainly follow the advice on the pressure relief valve service.

Dan,
After reading those threads that certainly makes sense. We will move this to the front of the line. I do not have an oil pressure gauge yet. Seems as though we should put that on the list as well. Will start to search the site for info. Thanks fellas.

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1968 Plymouth Valiant-225-more door.

thank you, thank you, thank you...I'd been seeing that at cold starts the oil light stayed too long for comfort; but just when starting in the morning. During the day it would "normal". Was looking for the "pressure relief valve" threads...

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'71 Dodge Dart, old Chrysler Corp.
My slant 6 will never, ever, be unrepairable