RalPh Posted July 20, 2005 Report Share Posted July 20, 2005 When hot, at idle, especially after getting off the highway at the end of the off-ramp, my idiot light (Oil Pressure) comes ON If I bring the engine just off-idle (900 rpm) it goes right out. The engine has to be at full temp for this to happen, just 10 mins of around-town driving won't do it, Hot off the highway, Hot summer day, just at Idle (makes me feel as if this is the earliest warning of more to come 97 STS, aggressively driven , 51,000mi, 10-30 Mobile 1 oil & Filter (tried another filter just in case), Oil Level right to the top..... I'm stumpped Link to comment Share on other sites More sharing options...
JimD Posted July 20, 2005 Report Share Posted July 20, 2005 I would suspect a failing pressure sensor. If you decide to replace it, use OEM parts only. Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
JasonA Posted July 20, 2005 Report Share Posted July 20, 2005 The oil pressure at idle is very low by design (like, 3-5 psi). The pressure switch has to be sensitive at that range to detect a low pressure. Your switch is probably just a HAIR out of the tolerance and when your oil is the thinnest (hot weather, just off the highway), the switch just BARELY thinks it's below the standard. As Jim said, a new (OE) switch will probably fix you up. Legitimate oil-related issues on the Northstar are incredibly rare. Jason(2001 STS, White Diamond) "When you turn your car on...does it return the favor?" Link to comment Share on other sites More sharing options...
Scotty Posted July 20, 2005 Report Share Posted July 20, 2005 I was going to say what Jason said, in the hot weather the oil is its thinnest. You might try changing to a different brand or adding a quart or two of 10W40 to raise the viscosity, make sure she is not overheating badly. Find Jason's post regarding High Mileage Oils, you might try going that direction. Mike Link to comment Share on other sites More sharing options...
RalPh Posted July 20, 2005 Author Report Share Posted July 20, 2005 First, High Milage Issues???... Don't think That's it Second, I'm sure by switching to a 20W oil I cure the light but,,, Would that just be putting off the inevitable???? IF it's not a simple bad switch. (I actually hadn't given that much thought OEM is the way for me! and I'll look for one today (anybody got a heads-up on where it's located?) 3-5 lbs is So Low that I can certainly see it being easily out of range so - Thanks Much for the TIP everybody! Link to comment Share on other sites More sharing options...
Scotty Posted July 20, 2005 Report Share Posted July 20, 2005 The POINT of bringing up the HIGH MILEAGE OIL was not RELATED to your mileage, the point is that you need to increase your viscosity a tiny bit, anyway you can accomplish that, go ahead. I doubt you need a switch but try it, maybe its calibration is off. If your engine is running excessively hot, that will cause this also as you can see by your description, check your running temps on average and report them. Personally I would ditch the Mobil One. I have seen this happen in an 86 Corvette, in the summer the oil light came on because the oil got SO hot its oil lost its viscosity and ability to maintain pressure, I do believe in the 86 Corvette it was bearing wear. Changing the oil helped, but keeping the engine cool also helped. Link to comment Share on other sites More sharing options...
RalPh Posted July 20, 2005 Author Report Share Posted July 20, 2005 Well, the dealer is out-of-stock will have one for me tomorrow... We'll see if it cures the light or not. The engine is NOT running "excessively hot" in Any Way, the cooling system is doing it's job just fine, I think its the highway speeds (80-85) -to- idle that is sure to bring it on. Interestingly enough, I too, (many years ago) had an 86 Vette I used Mobil 1 in it also but never had any trouble. I like Mobil 1 very much and want to continue to use it. I can't see any reason NOT to be able to if the engine is all it should be. I found the switch (off the filter adaptor) and looks like a quick job to replace, - I'll let you know how it turns out!!! Link to comment Share on other sites More sharing options...
Scotty Posted July 21, 2005 Report Share Posted July 21, 2005 Sounds like you know what it is, Good Luck Me I am not a fan of Mobil 1, its not necessary if you ask me. On my 4.9 the number one main bearing KNOCK was twice as loud with Mobil 1, I'll never use it again for that reason, its supposed 10W viscosity didn't act like 10W in my 4.9. It was especially loud after a long 600 mile trip and the engine was HOT in 90 degree heat with Mobil 1, changed to 10W40 the knock was gone for the return trip.. Link to comment Share on other sites More sharing options...
RalPh Posted July 21, 2005 Author Report Share Posted July 21, 2005 Anyone need a Used Good Oil Pressure sw? -hehe Still got that flickering light..... So now I guess I make some changes in the oil, disturbs me though,,, Either, The pump is not producing what it did last summer (and only 6K miles ago) Or Clearences within the engine have increased to the point where it can no longer "keep-up" (with this particular, admittedly thin motor oil) NOT happy in either case, with only 50K mi. it should be OK with it So, maybe I drain out a quart or two and replace it with conventional 10-30 or 1/2 a bottle of STP! or change it all (%61 left on the DIC) As for the thought that Mobil 1 isn't really necessary... I think of it like carrying a gun, I'd rather have it and not need it, than need it and not have it And if I have truly, slightly starved parts of the engine for oil at times... Maybe it's better that those parts last layer of oil was synthetic? (even if the oil itself Was the cause ) Link to comment Share on other sites More sharing options...
JasonA Posted July 21, 2005 Report Share Posted July 21, 2005 I've never known anyone who had a car with "low pressure" where a new pressure switch didn't fix it. Yeah, it "should" be okay with thin oil, but it's not necessary nor recommended. Even our resident GM powertrain engineer who has worked on the Northstar engine recommends good conventional oil. Try a good conventional 10W-30 (even a High Mileage type oil) and see what happens. I'll bet it'll fix you right up. Me, I'd rather have a conventional oil servicing all of my engine parts than a synthetic oil servicing some of them. Jason(2001 STS, White Diamond) "When you turn your car on...does it return the favor?" Link to comment Share on other sites More sharing options...
RalPh Posted July 21, 2005 Author Report Share Posted July 21, 2005 I'm sure it will too. I've know from the begining that increasing the viscosity would "bump" the pressure. Still like to know why it would suddenly be necessary though..... Link to comment Share on other sites More sharing options...
Scotty Posted July 21, 2005 Report Share Posted July 21, 2005 Ditto Jason Don't be surprised that when you use a GOOD grade of 10W30 that light stays off... Who knows maybe your current crankcase of oil had gotten diluited in some way and thinned out Link to comment Share on other sites More sharing options...
RalPh Posted July 25, 2005 Author Report Share Posted July 25, 2005 Update: Over the weekend I drained out 2 quarts of the Mobile 1 and replaced it with 2 quarts of Penzoil 10W-30. Still flickers Next, I'll drain the oil completely (and filter) and replace it with regular 10W-30.... That better do it!!!! Link to comment Share on other sites More sharing options...
mike5514 Posted July 25, 2005 Report Share Posted July 25, 2005 take the oil filler cap off and check to see if your are getting oil up to the rockers at idle, if not rev the engine and see if oil appears. Do a oil pressure check. Got a 4.1 from a junk yard once, it went 18000 mi. and did the same thing changed the pump and main/rod brgs. no help. It had Mobil 1 in it also. I dont use mobil 1 any more. Mike Link to comment Share on other sites More sharing options...
Scotty Posted July 25, 2005 Report Share Posted July 25, 2005 Update:Over the weekend I drained out 2 quarts of the Mobile 1 and replaced it with 2 quarts of Penzoil 10W-30. Still flickers Next, I'll drain the oil completely (and filter) and replace it with regular 10W-30.... That better do it!!!! I hope so too Ralph Link to comment Share on other sites More sharing options...
STS Posted July 25, 2005 Report Share Posted July 25, 2005 What kind of filter are you using? I suspect that an oil and filter change will do the trick. On another note, does anyone know if you can read the oil pressure on the digital display? Link to comment Share on other sites More sharing options...
mike5514 Posted July 25, 2005 Report Share Posted July 25, 2005 STS No Mike Link to comment Share on other sites More sharing options...
bigjayzway Posted July 25, 2005 Report Share Posted July 25, 2005 I am not a fan of Mobil 1 either....It gave me problems in my Yukon. I switched to Valvoline, and have stayed with it for years, with no problem. Big Jay Life is too short to grow up! Link to comment Share on other sites More sharing options...
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