News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

1968 deville oil light blinking at idle

Started by Lennon_68, August 21, 2021, 09:40:44 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Lennon_68

Hi all!  I'm a proud new owner of a 1968 Deville but I must admit I've never been a big car guy although I'm not at all afraid to dig in and get my hands dirty.  My grandpa had one and I have fond memories of riding in it so I've always wanted one. Last weekend I came across the right one at the right price and took the plunge. 

Its got a few mechanical things I'd like to get sorted out before I start cruising around in it.  First of which is this blinking idiot light.  It doesn't blink all the time, only after the engine is warm and only at idle in gear.  I first replaced the oil sending unit hoping it was just a misread but I'm getting the same results with the new one in there.

Prior owner suggested I increase the idle while in gear.  I started searching for info on how to do that today and that led me down a rabbit hole of vacuum tuning videos.  I'm looking for advice on what my next step should be.  Some of the options I know I have:

1.  Increase idle in gear...  If so how do I do that lol.

2.  Add an oil pressure gauge to get a better glimpse at whats going on.  I'm not too knowledgeable here either.  I know I could use the same port as the oil sending unit...  mechanical is much cheaper but is there a real downside... I could tee off and have both the idiot light and gauge I believe... or I think there's other ports somewhere.

3.  Tune the engine for vacuum and rpm then see if I still have the issue?  I think I know some folks that would help me with this and may have the equipment.

4.  Replace the oil pump. 


Any help would be greatly appreciated!

V63

Yes, you can T off that port with a gauge and a gauge is a good place to start. Verify the oil viscosity and maybe add Lucas oil stabilizer. Verify gasoline is not contaminating the oil from defective fuel pump ? Do you hear any engine noises or knocking?

hornetball

When was the oil last changed and what viscosity was used?  You might want to do an oil change just to make sure the old oil isn't watered down with fuel or something like that.  Also, verify that you have the proper idle speed per the FSM (you should buy one -- DVD online).

The oil pump on the 472 is external and very easy to replace.  If the low oil pressure condition persists, then I would remove the oil pump and inspect it per the FSM.  If it's worn beyond limits, then replace -- they're not expensive.  It could also be that the bypass spring in the oil pump needs to be shimmed or replaced, which is also easy.  If the oil pump checks out, then you need to go deeper into the engine.

I would minimize driving it until this is resolved though.  That idiot light is there for a reason.

Lennon_68

Thanks for the replies guys!

How do I verify the oil is not getting contaminated?  I don't hear any knocking although seller said he thought he did at one point.  When we were driving it occurred again but sounded more like an exhaust leak of some kind (sounded like puffs of pressure being released more than something tapping)... that was his opinion as someone that knows stuff and mine as someone that doesn't know much but has had an engine or two tick on me.

Oil was changed right before I test drove it.  The seller said he was thinking about putting 20w50 in.  Then when I picked it up he had changed the oil again.  Didn't use the heavy weight but added something that he had found suggested online.  I can get the details if needed.

How do I check idle speed?  Thinking I need one of those friends with knowhow for that but am interested in learning.

For the time being I'm limiting driving to about a mile.  Basically just giving test rides to a few friends (reluctantly although they don't know that).  Other than that it will remain parked.  I don't want to end up with major engine damage (fingers crossed).

TJ Hopland

Changing the oil on a car just before you sell seems kinda strange.   Find out what grade of oil was put in and what and how much additive was used.

For contamination just smell it to see if it smells at all like gas.   Also monitor the level to make sure its not rising. Gas from the fuel pump isn't a real common issue with these engines.

Having the engine internals worn enough to be bleeding off oil pressure is not at all common with this family of engines.  Its possible but would be the very last thing on the list.  Most likely thing is actually that the oil pickup screen is clogged full of pieces of the cam sprocket teeth and maybe some valve guide seal bits which were also plastic.   2nd likely cause which can be related to the first is worn oil pump from chewing on that plastic and other crud.  The stock pump body was aluminum so it doesn't take a lot to damage it. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

TJ Hopland

You asked how to check RPM,  a multimeter with automotive functions like this one would be the first of many tools to buy.   I didn't spend a ton of time searching but this one looks like it would do pretty much everything around the car and house most people would ever want to do so well worth the $50.   For the car it does dwell and rpm which you don't find on most meters but this one also has all the usual meter settings like volts amps and ohms. 

https://www.amazon.com/Actron-CP7677-Automotive-TroubleShooter-Multimeter/dp/B0002LZU7K/ref=asc_df_B0002LZU7K/?tag=hyprod-20&linkCode=df0&hvadid=312089957955&hvpos=&hvnetw=g&hvrand=16826790795192377944&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019543&hvtargid=pla-568627930766&psc=1

Actron is a big auto tool brand so I'm sure that model is available pretty much everywhere auto parts are sold.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Lennon_68

#6
I hear you on it being odd to change oil before a sale but (and I realize this is another red flag)  he actually only owned the car foe about 3 months.  Had put work into it and had just gotten it running with the help of a mechanic but then decided to sell as it barely fit in his garage and he wouldn't be able to work on it.  I chose to believe him but I realize that could have been a line.  I don't think anything nefarious is going on with changing the oil though.  The second oil change he did was after the sale was final, title was transferred and he was paid.  I truly believe he just cared about the car.

I gave the oil a sniff test and it doesn't smell of gasoline. 

I have the receipt for the last oil change.  He used 15w40 and the receipt says "pt can marvel oil".  Manufacturer says "mam" part#12.  I can ask him if its not clear what that is...

So is oil pressure gauge my next move or idle?  Any concerns about a mechanical pressure gauge?  I gather (could be wrong) that I have to run an oil line to wherever I want the gauge to be located unless I buy an electric gauge which looks like costs about $90... 

Or should be looking into cleaning that screen?

TJ Hopland

It sounds like a reasonable story.  15w-40 is most likely a diesel oil and as mentioned before a popular option so no concern there.   Marvel mystery oil is also a popular additive that doesn't make a lot of sense for a low oil pressure issue but doesn't concern me enough to want to change it again right away.

Can you identify the oil filter brand?  If its orange no one likes those and since its easy and cheap maybe worth picking up a wix 51049 or 51258 or Napa Gold 1049 or 1258 just to make sure its not a crappy filter.  We just had a oil filter discussion and no one said anything bad about the wix.  Some still sticking with AC but didn't hate the wix which is really something when it comes to brands.    Again its a long shot but its cheap and easy.   Don't forget you will need to top off the oil if you just change the filter.   Even walmert has diesel oils so finding a 15w-40 should not be hard,  trick may be finding it in a quart bottle,  you may end up buying a gallon but since they come in gallons you will need more than one bottle for the next change so having a partial won't be that big a deal.

The oil gauge will likely be temporary so at this point might as well just get the run of the mill mechanical gauge with the plastic hose that attaches it and temp it in under the hood or in the car if you can find an existing hole to shove it through.  Note that if the hose gets damaged it will pump oil out.   If you think you want to keep a gauge then spend the money to get something electric that looks decent.  Electric is usually easier to run the lines for and won't have the issue of squirting hot oil inside the car if its damaged.     The T fittings you can get at home depot or hardware store sorts of places.  Someone else will have to confirm but I think you need 5/16" NPT threads which is bigger than what is most common but the gauges usually come with the adapter.

Cleaning out the screen you have to drop the oil pan which can be done in the RWD cars without removing the engine.   You would normally do that when you replace the timing chain set which is usually the reason for digging into the engine in the first place.   Checking the timing chain condition is a little more tricky on these things.   Easiest way to get a clue is remove the distributor cap so you can see the rotor then rock the crank back and fourth and see how far you have to turn before the rotor changes directions.   Typically you would do that by putting a breaker bar on the crank bolt at the front of the engine.  Cads didn't come with this bolt so you have to get one or find another way to rock it.    Strap wrench around the crank pulley may be an option if you have a helper.   Pull out the spark plugs then maybe you could do it by grabbing things like the alternator fan or power steering pulley.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Lennon_68

The receipt shows Wix51258 so we should be good there.  Looks like he made good choices on oil and filter.

I'll pick up a mechanical gauge and just put it under the hood.  I think I saw the same 5/16 npt listed somewhere I was reading but the numbers do start to all look the same.

Did some digging and looks like I'd remove the oil pan to get at the pickup screen.  Guessing I'd need to buy an oil pan gasket if I was planning to pull that off?  Or can you reuse the gaskets on these older cars?  I also have some oil seaping around the valve covers so am ordering replacement gaskets for them.  I know very little about this stuff but thinking that seaping couldn't be enough to cause the low oil pressure (it seems it would have to be basically spraying out to cause the low pressure and it would be painfully obvious).

I'm way out of my element when you start talking about checking the timing.  If that's something that I really should do and if/when I pull the oil pan off I'll do some more digging.  If it was just for fun I wouldn't mess with it though.


Thanks again for all the input as well.  I'm so glad I joined this forum!  It's awesome to see others with realworld experience with this car/engine that are willing to take time to help a stranger on the internet out.

TJ Hopland

In a general terms the most common reason an 'old' engine suffers from low oil pressure is general wear.  The oil is under pressure and being fed to all the bearings which are just flat pieces of metal in most engines.  When new the clearances between the shaft and bearings are carefully calculated to let just enough oil out of the feed passage to provide the ideal film thickness for everything to be happy.   Basically the shaft is riding on a film of oil, not direct metal to metal. 

As things wear which can be worse if you use low quality oils and don't change it often the clearances open up so more oil can flow through rather than creating the proper film layer.  This may actually increase the wear which increases the flow and the more flow the lower the pressure will be because there just isn't the original restriction.  Its basically just pouring out rather than being squeezed evenly.   Depending on the design of the engine some engines have major issues because very high load bearings may be at the end of the line where the pressure is the lowest on a worn engine. 

This family of Cadillac engine was a good design that was fairly overbuilt using quality materials and most of them got used pretty gently and got pretty good care when compared to say your typical Ford or Chev motor.  Those were built out of lower quality materials and cost was a major design consideration so maybe they cut some corners.   They were also less expensive cars that sometimes got abused and didn't get the best care.    Its pretty rare to open up one of the Cad engines and see significant wear.   If you have to replace hard parts its most often damage from sitting.

The timing thing is that in that era GM used a plastic covered cam sprocket for the timing chain.   Age and miles were not at all kind to these things and that was back when these were only 10 year old engines,  its real bad if you have an original that is now in the 50 year old range.   The plastic WILL eventually crack and fall off.  Luckily the aluminum hub sort of has teeth that the plastic was molded to and that can sort of engage the chain for a while and it may sort of stay in time.    Even at this age there are still a decent number of original plastic ones out there so its not just a given that it had to have been replaced at some point already. 

The process of rocking the crank isn't to check the timing per say its to see if there is slack in the timing chain which is likely caused by the plastic cracking and falling off.   If there is pretty much no slack the rotor will change direction pretty much instantly when you reverse the direction you are turning the crank pulleys.   If that is the case you can put off further inspections for a bit and move on to other things.   If it does take say an inch or more of turning the crank before it changes directions its shot and could fail at any time so you would want to get on changing it which also means dropping the pan to get a proper seal and cleaning out the crap. 

If there is no apparent slop then you can move onto other things first but at some point you will want to pull either the distributor or fuel pump and try to get a peek at the sprocket to see if its metal or plastic.  Its possible that someone replaced it but didn't drop the pan so its still full of crap at which point you can just pull the pan and clean it.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

savemy67

Hello Lennon_68,

When I was 17, I bought my fourth car from out of state.  I was the victim of a nefarious seller.  When I returned to my home state I vowed never to let that happen to me again.  I found a mentor - a mechanic in the U.S. Air Force - and I learned how cars worked, from the brakes through the transmission and engine, to the heater.  Whether or not you want to do your own work, I suggest you get the factory shop manual so you can read about how your car's systems work.

Attached is a photo of my mechanical oil pressure gauge "T'd" into the sender port at the back of my engine, and a photo of the gauge (and a vacuum gauge), mounted under my hood.

The shop manual will describe the procedure for adjusting the idle speed - if your car has its original carburetor.  If not, you can refer to the manufacturer of the carburetor for instructions, or find someone who is knowledgeable.  Note that if you raise idle speed without using a tachometer, you could raise the idle speed too high for smooth engagement of the transmission from Park or Neutral.

Poor vacuum can affect idle speed.  On these cars, obtaining proper vacuum is not as easy as it looks because there are many vacuum connections (e.g. power door locks, power brakes, power trunk release, power E-brake release, climate control), all of which can leak which in turn can affect idle.

From least laborious/difficult to most laborious/difficult:

adjust idle speed
install mechanical oil pressure gauge
replace (or rebuild) oil pump
drop oil pan and clean oil pick-up screen - if bits of plastic are found in the pan or screen,
remove engine front cover and replace cam sprocket and timing chain

The above tasks range from 5 minutes of work to all day.

Your post indicates that when the engine, and therefore the oil, get warm, the idiot light blinks.  This would indicate that the idiot light sensor/oil pressure sender is not seeing enough pressure at idle when the oil is warm.  Your post also indicated that the previous owner used 40 weight oil.  Many people use higher weight oil on high mileage (read worn) engines because they believe many of the clearances have gotten larger than specification.  What is the mileage on your car?

Your 472, if it is in good condition, should have no problem using 30 weight oil, provided you do not live in Death Valley.  Pumps, including your oil pump, do not create pressure.  Resistance to flow creates pressure.  Excessive bearing clearance would decrease resistance to flow thereby decreasing oil pressure.  If the oil pick-up screen was blocked, as engine rpm increased the pump would want to increase oil flow, but due to a blockage, insufficient flow would result.  This varies depending on the percentage of blockage, but since your post does not indicate a problem at higher RPM, the screen may not be blocked, or blocked enough to affect oil pick up.

The quick and easy:  increase idle speed (within the limits of shifting the transmission comfortably into gear), and use 40 weight oil if you do not live in Minnesota (TJ lives in the frozen wastelands north of Iowa  :))

The slow and difficult:  determining your bearing clearances, and the condition of your oiling system.

Respectfully submitted,

Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

Lennon_68

#11
Hi savemy67!  Thanks for the elaborate and informative response.  First and foremost I DO happen to live in Minnesota... and a good bit further north than TJ even. 

I have a couple updates.  I did another demo drive today and it performed fine for most of the trip but we heard the engine noise again.  The previous owner had thought it was a tick... then thought it was an exhaust leak of some sort... but today it definitely sounded like a tick.  It only shows up once the engine is warmed up.

Just now my brother in law and I finished adding a mechanical oil pressure gauge.  We added a tee to keep the idiot light and there was an easy spot to go through the firewall so I have it mounted on the bottom of the dash where someone had previously screwed something on.  When the engine first starts and its idling high the pressure is around 25psi.  When the idle settled down (about a minute after starting?) The pressure settled in around 10psi.  When I put it in drive the idle drops considerably and the pressure drops to almost nothing.  Reverse is even worse with idle basically at nothing and not moving thr needle at all.

I do have the shop manual and will take a look at how to adjust the idle as my next step.  I also noticed what I think are vacuum lines not hooked up correctly?  By the distributor there's what I think is a vacuum line thats just routing back to itself.  Meanwhile there's some capped ports on the carb that look like they could be vacuum ports. 

Update.  I found the section of the shop manual on idle adjustment.  I plan to tackle that next.  We leave tomorrow for a week long camping trip though so it will be a bit before I can tinker with anything.  For the idle adjustment whats the cheapest way to measure rpm?  Maybe i can check a tool out at oreilly or autozone?

TJ Hopland

That carb looks pretty nasty.  With the outside looking like that its got to have been a while since its been gone through so that should proabbly go on the to do list but at this point it doesn't sound like it needs to be at the top of the list.

It does look like you got some modifications to the vacuum system.  That's not for sure a bad thing but you will have to get a diagram and figure out what you still have and what was supposed to be there and we can then help you figure out what you may need to repair and re connect.   I don't work on that many that early but it seems like your carb has more ports than I was expecting like its for a later car unless maybe it was originally a CA emissions car?

Oil pressure does sound low even if the idle is a little low.  You want to see at least 5 warmed up and in gear.

Unless you get lucky and find something used I think the best value would be to buy a multimeter with the automotive functions like I mentioned above.   You maybe can buy something cheaper than that $50 but its not going to be as versatile on the car and around the house.   If you are going to get into fixing just about anything electrical yourself a multimeter is a must have tool.     I'm not sure a parts store will have anything in their tool loan stuff that will read rpm on an old car.  You have not needed a timing light or dwell tach meter on a car for 30 some years now.       



StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Lennon_68

#13
I do have a very nice fluke multimeter that I got from a friend.  I'll take a peak at the interwebs and see if there's a way to use it for rpm even though it doesn't have automotive functions...

Update.  Did some digging.  I have a fluke 21 series ii.   Also looks.like i can use any multimeter as long as it measures hz.  Not sure yet if this does or not though

Update 2.  Looks like this does not measure hz but I should be able to find a friend with one that does now that I know what to look for.  We leave for camping in a few hrs so no more tinkering for a bit.  Thanks again for all the assistance.  I'll be back with updates and more questions im sure! 

James Landi

"J"   if you can find the owner's manual for this car, it states the a blinking oil light in hot weather at idle in gear is NORMAL.  Don't drive yourself crazy.   My suggestion... drive the car carefully--- knowing that it's over a half century old, has 5,000 moving parts, and they all age and are not (again NOT) to original specifications.  You've sufficient reserve power in that engine to destroy the transmission, motor mounts, and associated running gear.  Drive it with care (i.e. burn rubber, slam it into passing gear, etc.).  Drive it with care (i.e. carefully)  and enjoy it. If you take care of this car, it will take care of you.   Hope this helps, James

Lennon_68

Thanks James!  Having added the pressure gauge I'm certainly more comfortable tooling around in it.  I do think there's an adjustment to be made but at least now I know its got enough pressure in most conditions (it seems I should still be worried about basically no pressure in reverse though).

  Either way I'm learning lots through this exercise which has been fun for me so far :)

TJ Hopland

You can look for an old used tool usually called a Dwell / Tach meter.    They are usually multiple one for sale in larger markets.   You can also find them on ebay.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

cadlove

James - which owners manual suggests a flickering oil light at idle is ok?

Just checked my '77 and '78 owner's manuals and they say to shut the motor off immediately?

If an oil light flickers something is wrong, so better to stop and check than eat your bearings. Yes in hot climates it can happen but I would suggest if that climate is your norm you need thicker oil. I've lived on the French Riviera with summer being 100F and used both 10w40 and now Valvoline VR1 20w50 weight and never had a flickering oil light. JP

James Landi

Hi John,

IF MEMORY SERVES, I recall this owner's advisory in owners' manuals from either my l956 model cars and/or my mid 60's Cadillacs-- alas, I don't have the text.   I went through the expense of having main bearing and connecting rod bearing changed out on a SDV back in the early 1970's, and still, occasionally, the light would flicker.  All said, I believe I'm in safe territory to suggest that 50 and 60's GM cars used idiot lights because the engine oil pumps provide weak pressure at idle, when hot, and in gear.  James

walt chomosh #23510

Hi guys!
  My 2cents is that when OP drops allowing the OP light to flicker (at idle) generally won't hurt the motor. The rocker arms is the last item in the oiling system and when it starts "talking" one needs to pursue the cause. (motor damage can result) The summer months can cause oil lights to flicker. A guy can shim the oil pump bypass spring to boost pressure. Heavier oil in the summer will put the light out. I believe someone mentioned Lucas oil additive....won't hurt a thing and sometimes can result in a happy motor....walt..tulsa,ok