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Ms. Wrench
Ms. Wrench, ASE Certified Technician
Category: Car
Satisfied Customers: 554
Experience:  ASE Certified Technician-10 yrs., Service Writer-Foreign, Domestic & Fleet, Alternative Fuel Expert
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I purchased a 1998 Cadillac deVille. I drove it the first ...

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I purchased a 1998 Cadillac deVille. I drove it the first evening 70 degree outside temp., everything OK. the following day was about 90 degrees, oil light kept flickering at a idle. Oil level OK, new valoline 10w30 by dealer. Oil light went out when idle increased about 50 rpm. Started on a trip, was caught in stop traffic water temp read 223 degrees normally about 198, computer read message "oil pressure low, stop engine immediately" Pulled to side of road, temp cooled down, restarted, no further problems but outside temp has been in 70-80''s range. Dealer mech says idle cannot be increased 50rpm because computer would recompensate. No smoke from exhaust. no single or double rap from engine. Cad customer booklet says only use 10-30, would 10-40, stp, slick 50 etc. solve problem? Dealer will not give me previous owner''s number so I can find out if they used synthetic oil. Going to head for Florida with their very hot temperatures so i am concerned. Thank You, XXXXX XXXXX


Due to the fact that there is no noise from engine at all there is a possibility that the problem is with the oil pressure sending unit. The problem would not be caused by the previous owner using synthetic oil, synthetic oil does not leave deposits that clog oil passageways-an oil pressure problem would be more likely to occur from switching to synthetic in an older engine because the synthetic will actually break deposits loose and clog up. If the previous owner used an oil such as Pennzoil that is known to leave alot of deposits behind there could be a flow issue somewhere in the system.

My first suggestion would be to have the oil pressure sending unit replaced-if the sensor is failing-it will detect low oil pressure at low RPM's when the temp is warm and the oil is thinner.

My second suggestion would be to flush the oil system-there are some shops that have equipment to do this, or there is an additive that can be added to the oil, then ran for 10-20 minutes at idle, then drained and the filter replaced. A molybdenum treatment such as Slick 50 may help, as would a nano technology treatment. The aggressive plateau honing and crosshatch used in the Northstar engine causes oil to stay in the cylinders and can provide lubrication to rings etc at extended high RPM's. Deposits can build up in the cylinders over time and may also be affecting oil pressure and consumption. There is a method for applying cleaner through the spark plug holes and a special vacuum to remove the debris-the dealer should have this equipment.

If neither the sending unit or a system flush helps the problem then you will need to have a mechanical oil pressure test done and further diagnosis on the oil pump condition.

Hope this helps, I'll be glad to assist more if you need it. Just post and let me know.

Thanks for using JA

Ms Wrench


Customer: replied 9 years ago.
I was told that switching from syn to oil OR viceversa could cause problems either way. Oil weight change to 10w/40. The 40 being good at higher operating temperatures question still exists. i personally have been using Quaker State since my 1950's racing days. I am not a chemist but what do you as a tech/writer consider the best oil. The sending unit had already been in my equation as it was always the easiest to change in my days. By now you reason that I'm an older person. I sure miss my small block days from back then. I was quite successful but had 6 kids and it became cubic money and brand sponsored so I stopped running at the Winter Nationals. Is there a way I can contact you if your ideas are successful. I am not knowledgeable on today's computer cars. Give me a 57 chevy, blindfold me and I can get it running at peak performance [they did this to me once as a test]. If your suggestions work, I will gladly accept. I will keep your reply in my "new" file so I can get you paid. I just need one person I can contact as a Tech advisor. Thank You, XXXXX XXXXX

Hello Mr Briggs,

I think on the Northstar I would stick with the 10/30. That engine is designed to get oil to stay in the cylinders and 10/40 wouldn't solve any of the problems you are having. If the problem is in the sending unit, a thinner viscosity would only make it worse, and if the problem is with deposits we need to go the route of getting the system cleaned up.

Quaker State is a good oil, the only brand I see alot of problems with is Pennzoil-it has something to do with paraffin I believe but I know it makes a mess especially if maintnenance isn't kept up. I recommend synthetic whenever possible, RedLIne is my preference. Ammsoil is a good product but I have had better experience with RedLine products.

I need to retract what I said in my earlier post about Slick50-it is actually a PTFE or Teflon additive and there has been much debate over its benefits as well as problems with it clumping up in some engines. Molybdenum treatment such as Restore are friction modifiers and reduce the friction between parts-resulting in reduced wear and increased efficiency. What is really interesting are the nano-technology treatments that are coming out now. I haven't had enough experience yet to recommend a certain product, but I know of several and I have seen some amazing tests. If you are interested I can forward you some info I have on nano treatments. Also if you are interested I can forward you more technical info on the oiling system features in the Northstar engine, the engineering allows it to run at 6000 RPM's for extended periods but also lends itself to common pressure issues such as the one you are having and also there are very common problems with oil consumption.

Let me know what happens after you get the sending unit changed out, and I would definitely recommend doing an oil system flush, like I mentioned, you may be able to get it done as a service at a shop, or there are canned products that work very well also.

You can keep posting to this question until we get it resolved, and any future questions you need help with you can request me and I will be notified. Keep me posted, I'll be watching for your posts.

Thanks for using JA

Ms Wrench


Customer: replied 9 years ago.
Reply to Ms. Wrench's Post: Hi, I remember when Paraffin based oil came out and we all refused to use it calling it "candle wax/oil] [in our race cars.] Restore might help by keeping heat down from less friction. this oil problem does not happen in cooler temperatures that's why I wondered about the 40 weight being thicker at higher temperatures. I am very interested in nano technology, I believe it may be the bio-tech of the future. Please send info. Please send info on oil system for Cad, also not sure where sender unit is located, older cars you could easily identify it. It was very common for small screw at head of sender to loosen losing contact causing a flickering in GM cars in 50's and early 60's. What canned flush products are available? We [there I go with old days} used to use oil and kerosense run to clean out engines and also auto trans. To up oil pressure, I would put a few small washers under pump spring. Could computer be malfunctioning, I know nothing about them. Grandkids set up this computer and keep it working. Thank You! Mr. Briggs
Customer: replied 9 years ago.
OOPS, I may have hit wrong key. Last reply I sent started with "Hi, I remember when Paraffin based" etc. Was it received? Thanks, XXXXX XXXXX
Customer: replied 9 years ago.
Need answer to post of 7/10 @5:58. Thank You Mr. bruggs

Hello Mr Briggs,

I'm glad you sent that reminder-I hadnt been aware that you were waiting for me to answer.

The oil sending unit is on oil filter adapter-top right side. It is much easier to replace without the filter being on.

Wynn's has a good oil flush product, as does CarQuest. The best way to go would be to find a shop that has the actual motor-vac system for the engine oil. If you give me your zip I can try to locate a shop that has that service, and give you a referral.

I will post some info on the nano products i am looking at now a little later. I've got to log off for a little while but I will be back soon.

Thanks for using JA

Ms Wrench

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Customer: replied 9 years ago.
Reply to Ms. Wrench's Post: Hi, zip is 20603. Let me know about nano tech products, sounds exciting. Mr. briggs
Customer: replied 9 years ago.
Ms. Wrench, hi, Mr. briggs here. Sorry, just got back from hot, hot Florida. Oil sender ok. I never received an answer back on my last question but I am going to release your fee because you have spent the time. god Bless, Mr. briggs