Jump to content

Photo

High Oil Consumption in Street NB

- - - - -

  • Please log in to reply
8 replies to this topic

#1
Carl

Carl

    Member

  • Members
  • PipPipPip
  • 57 posts
  • Location:United States
  • Region:California
  • Car Year:1990
  • Car Number:38

I realize this is not exactly a Spec Miata question, but this should be the place with the knowledge.

 

My son's 99 Miata is drinking oil at the rate of about 1 qt per 300 miles.  The PCV has been replaced.  Cold compression is 210psi in all cylinders.  Can't see any blue smoke, although we need to investigate that more closely during transient conditions. There are no external leaks. It does have the "EGR" engine code, but that does not seem like it would be related to oil consumption, since it is pushing exhaust back into the intake (the oil consumption might have caused the EGR code though).  

 

My question is whether or not it is in the realm of possibility for this much leakage from bad valve stem seals?  If not any other suggestions?

 

Thanks for any thoughts you might have.

 

Carl  



#2
Tom Hampton

Tom Hampton

    Egregious Member

  • SMembers
  • PipPipPipPipPip
  • 1,961 posts
  • Location:Mckinney, tx
  • Region:South west
  • Car Year:1992
  • Car Number:41

front and rear crank seals...

 

I was losing oil at about the same rate on my daily driver (1990).  I replaced both seals 2 months ago as part of a water pump replacement and a clutch/flywheel job. I just added my first quart of oil since replacing the seals.  I drive about 1500mi a month, so 3000mi give or take. 


-tch
Build: www.tomhampton.info

video: vimeo.com/tomhampton

Support: X-Factor Racing

 

I didn't lose, I just got outspent!

Beta-Tester - Assisted us with beta testing the website. Donor - Made PayPal donation Bona fide - A bonafide Spec Miata driver

#3
Carl

Carl

    Member

  • Members
  • PipPipPip
  • 57 posts
  • Location:United States
  • Region:California
  • Car Year:1990
  • Car Number:38

Do those seals leak to the outside or does the oil get sucked into the engine and out with the exhaust?



#4
Tom Hampton

Tom Hampton

    Egregious Member

  • SMembers
  • PipPipPipPipPip
  • 1,961 posts
  • Location:Mckinney, tx
  • Region:South west
  • Car Year:1992
  • Car Number:41
They leak to the outside. But, only when the engine is operating though, and under oil pressure.

Oil from the front seal leaks onto the crank pulley and gets flung onto the belly pan, and other surfaces in plane with the pully...where it mixes with other dirt, etc. So, it doesn't tend to drip onto floor when the car is stationary.

Similarly with the rear seal, it flings onto the interior of the bell housing. there is a weep hole in the bottom of the bell housing. So, sometimes a little oil may leak out of there and drip. But, my experience with two street miatas (one at 150k and the other at 230k) is that the leak out the rear seal has to be pretty big before you ever see a drip from the weep hole make a spot on the ground.

-tch
Build: www.tomhampton.info

video: vimeo.com/tomhampton

Support: X-Factor Racing

 

I didn't lose, I just got outspent!

Beta-Tester - Assisted us with beta testing the website. Donor - Made PayPal donation Bona fide - A bonafide Spec Miata driver

#5
Carl

Carl

    Member

  • Members
  • PipPipPip
  • 57 posts
  • Location:United States
  • Region:California
  • Car Year:1990
  • Car Number:38

Thanks Tom.  I am pretty sure that the engine is totally dry, but will check again.  We actually replaced the front seal a couple of months ago, so have kept an eye on that pretty closely.  Also pressure washed the underside of the car at that time.  



#6
FTodaro

FTodaro

    Veteran Member

  • SMembers
  • PipPipPipPipPip
  • 2,991 posts
  • Location:Columbus Ohio
  • Region:Great Lakes
  • Car Year:2001
  • Car Number:35

Carl i will let one of the motor builder chime it but you could be consuming the oil even though the you have compression, two of the rings are compression and one is an oil ring so two different jobs. some times you will not see the oil blue tinge until its under a load. Bottom line it can be difficult to detect at the tail pipe. Go on line buy one of those cheap bore scopes and see if the cyl walls are scored. 

BTW we don't mind talking about engines it keeps us off of discussing parity between the classes.


  • Alberto, Danny Steyn and lillyweld like this

Frank
TnT Racing
SCCA Ohio Valley Region
Chairman, SCCA Great Lakes Divisional Series Committee.

Make it Rain - Made Paypal donation of $100+ We have a Winnah! - Won their 1st race... Congratulations! Bona fide - A bonafide Spec Miata driver Donor - Made PayPal donation

#7
Danny Steyn

Danny Steyn

    Zulu rain warrior

  • SMembers
  • PipPipPipPipPip
  • 2,415 posts
  • Location:Fort Lauderdale
  • Region:FL
  • Car Year:1999
  • Car Number:39

and if you ever feel your clutch slipping on gear changes under load, say heading up a hill when you shift from 3rd to 4th, it signals that you have a pretty leak in the rear seal


Danny
Danny Steyn Racing | DSR YouTube Channel
Danny Steyn Photography | Adept Studios | Ocean MachineryOPM AutosportsRossini Racing Engines | G-Loc Brakes | 

2018 SCCA Runoffs Champion, NASA Champion, Hoosier Super Tour Champion, June Sprints Winner

2016 June Sprints WInner, ARRC Winner, NASA Eastern States Championships Podium

2015 Eastern Conference Majors Champ, June Sprints Winner, ARRC Winner

2014 NASA Eastern States Championship Runner Up.

2013 SEDiv Driver of the Year, Eastern Conference Majors Champ, SEDiv National Champ, ARRC Winner, Runoffs Podium

2011 SEDiv Driver of the Year, SEDiv National Champ, ARRC Winner, Palm Tree Quad National Champ, SEDiv ECR Champ
2010 June Sprints Winner, ARRC Winner

2009 SARRC Champ, SEDiv ECR Champ, FES Champ
2008 SEDiv ECR Champ

June Sprints winner  - June Sprints winner Series Champ - Won a points based series in a Spec Miata ARRC Champion - Won the ARRC Race in a Spec Miata We have a Winnah! - Won their 1st race... Congratulations! Bona fide - A bonafide Spec Miata driver NASA Champs Winner - NASA Champs Winner June Sprints winner  - June Sprints winner ARRC Champion - Won the ARRC Race in a Spec Miata ARRC Champion - Won the ARRC Race in a Spec Miata Majors Winner - BFG Supertour Winner -

#8
Tom Hampton

Tom Hampton

    Egregious Member

  • SMembers
  • PipPipPipPipPip
  • 1,961 posts
  • Location:Mckinney, tx
  • Region:South west
  • Car Year:1992
  • Car Number:41

and if you ever feel your clutch slipping on gear changes under load, say heading up a hill when you shift from 3rd to 4th, it signals that you have a pretty leak in the rear seal


My first donor car had a leak that bad. Clutch would slip climbing a hill, even fully engaged. Talked the seller down on price because, "whew! Clutches are expensive and hard to change."

...

Ahem...pay no attention to the racing clutch already in my garage.

-tch
Build: www.tomhampton.info

video: vimeo.com/tomhampton

Support: X-Factor Racing

 

I didn't lose, I just got outspent!

Beta-Tester - Assisted us with beta testing the website. Donor - Made PayPal donation Bona fide - A bonafide Spec Miata driver

#9
Carl

Carl

    Member

  • Members
  • PipPipPip
  • 57 posts
  • Location:United States
  • Region:California
  • Car Year:1990
  • Car Number:38

I will take a look in the cylinders with a boroscope and see what things look like.  

 

At the rate oil is disappearing, I don't know how it could be leaking externally since there is not a drop of oil anywhere on the outside, including the weep hole on the bottom of the tranny.  The clutch is definitely not slipping either.

 

 

Carl






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users