EXCESSIVE oil leak - Burning off exhaust, but from where?

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

79dentside

Full Access Member
Joined
Nov 20, 2019
Posts
369
Reaction score
383
Location
Kansas
First Name
Brandon
Truck Year
1979
Truck Model
GMC Sierra Classic
Engine Size
350
Hey guys, I have a 350 that I can’t stand to drive anymore. I have an excessive wave of burning oil come into the cab after every acceleration. Problem is, I am lost. I cannot find my leak. I’ve done valve cover gaskets, but it is still there. Bellhousing is clean, I suspected it might be dripping from the sender, that is not the case. I thought maybe it is blowing oil out the breather, that is not the case.

I even had a buddy video tape the engine while I two-footed it and put some load on the engine. I cannot find my leak.

What would cause an excessive amount of burning oil to fill the cab? I’ve had this same smell before, but because I had a valve cover split but it bellowed smoke from under the hood on that engine.

Side notes:
*No blue smoke in exhaust
*No smoke from under the hood while driving
*changing the valve cover gasket helped, but it was never perfect.
*Oil filter housing tends to be excessively greasy
*currently, edges of the valvecovers are not wet.

1st picture was with the new valve cover gasket. I degreased the engine completely down to where you could see the block paint.

2nd picture was yesterday, oil filter housing already has oil all over it and it’s only been 5 or 6 months.
 

Attachments

  • 6840D7DD-E4C3-4644-AFE3-797EFE72DD2D.jpeg
    6840D7DD-E4C3-4644-AFE3-797EFE72DD2D.jpeg
    126.1 KB · Views: 74
  • C25BC246-99E6-40FF-A770-45CBB2CA73AF.jpeg
    C25BC246-99E6-40FF-A770-45CBB2CA73AF.jpeg
    89.5 KB · Views: 65

DoubleDingo

Full Access Member
Joined
Jul 3, 2012
Posts
10,188
Reaction score
14,500
Location
Right where I am
First Name
Bagoomba
Truck Year
1981, 1965
Truck Model
81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
Engine Size
Carb'ed Vortec 350; 1972 L48 350
Back of intake? Are the valve cover mounting surfaces flat? Meaning are they bent from being torqued too much?

I had a similar leak, thought it was the rear main. It turned out to be the back of the intake.
 

79dentside

Full Access Member
Joined
Nov 20, 2019
Posts
369
Reaction score
383
Location
Kansas
First Name
Brandon
Truck Year
1979
Truck Model
GMC Sierra Classic
Engine Size
350
They are snug, I did not want to strip the bolts.

My rear main does seap a little, would that burn off the exhaust?

Here is a pic of the back of the block. It is dry. Rear main does seap a bit. Noticed that when I pulled the cover and did a starter.
 

Attachments

  • 176A6E75-2D3A-4A5F-8965-520E144A437C.jpeg
    176A6E75-2D3A-4A5F-8965-520E144A437C.jpeg
    118.6 KB · Views: 58
  • F6A763D3-4ED1-4D3C-82B5-B442A57A8188.jpeg
    F6A763D3-4ED1-4D3C-82B5-B442A57A8188.jpeg
    103.1 KB · Views: 58
  • F9F8C4AD-4EE2-410B-A453-097FDBF10E18.jpeg
    F9F8C4AD-4EE2-410B-A453-097FDBF10E18.jpeg
    90.2 KB · Views: 57

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
29,114
Reaction score
23,984
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
Is there an oil sender down by the oil filter?
 

PrairieDrifter

Full Access Member
Joined
Dec 28, 2014
Posts
3,463
Reaction score
4,577
Location
North Dakota
First Name
Mason
Truck Year
84,79,77,70,48
Truck Model
Suburban k10, bonanza k10, c30 C&C, c10, gmc 1/2ton
Engine Size
350, 350, 350, 350, 350
Intake or valve covers. Valve covers and front and rear intake are why these trucks get greaseball motors, Ive found that when these are properly sealed the whole engine stays very very dry.
 

79dentside

Full Access Member
Joined
Nov 20, 2019
Posts
369
Reaction score
383
Location
Kansas
First Name
Brandon
Truck Year
1979
Truck Model
GMC Sierra Classic
Engine Size
350
I will check the valve covers again, but I ran my finger around them. They are not wet. Back of the motor is not wet either.

No sender on the housing, but there is a plug. I suppose maybe that is leaking?

I put a new pcv valve and hose on. Also, I did test to see if it was over pressurized. I pulled the breather and reved the motor. No smoke.

Also, I had a buddy video tape the engine while I stuck it in gear and really loaded it down to see what was spraying under pressure and under load. Nothing from the breather.
 

rusted nuts

Full Access Member
Joined
Mar 5, 2023
Posts
809
Reaction score
1,418
Location
Pa.
First Name
Jeffrey
Truck Year
1979
Truck Model
k20
Engine Size
4cly diesel
Hey guys, I have a 350 that I can’t stand to drive anymore. I have an excessive wave of burning oil come into the cab after every acceleration. Problem is, I am lost. I cannot find my leak. I’ve done valve cover gaskets, but it is still there. Bellhousing is clean, I suspected it might be dripping from the sender, that is not the case. I thought maybe it is blowing oil out the breather, that is not the case.

I even had a buddy video tape the engine while I two-footed it and put some load on the engine. I cannot find my leak.

What would cause an excessive amount of burning oil to fill the cab? I’ve had this same smell before, but because I had a valve cover split but it bellowed smoke from under the hood on that engine.

Side notes:
*No blue smoke in exhaust
*No smoke from under the hood while driving
*changing the valve cover gasket helped, but it was never perfect.
*Oil filter housing tends to be excessively greasy
*currently, edges of the valvecovers are not wet.

1st picture was with the new valve cover gasket. I degreased the engine completely down to where you could see the block paint.

2nd picture was yesterday, oil filter housing already has oil all over it and it’s only been 5 or 6 months.
What makes You thing it is burning on the exhaust? How is Your transmision working/ I have seen this happen on a trans that was going bad.
 

79dentside

Full Access Member
Joined
Nov 20, 2019
Posts
369
Reaction score
383
Location
Kansas
First Name
Brandon
Truck Year
1979
Truck Model
GMC Sierra Classic
Engine Size
350
I can smell it burn. Also, I put some marvel mystery oil in the crank case as I do most of my cars and from time to time, I can specifically smell that burning.

Transmission shifts fine. What would cause that? Are you saying implying like a burnt clutch smell? Trans was supposedly rebuilt by a PO. Has a stall and a shift kit. Case looks clean.
 

rusted nuts

Full Access Member
Joined
Mar 5, 2023
Posts
809
Reaction score
1,418
Location
Pa.
First Name
Jeffrey
Truck Year
1979
Truck Model
k20
Engine Size
4cly diesel
I can smell it burn. Also, I put some marvel mystery oil in the crank case as I do most of my cars and from time to time, I can specifically smell that burning.

Transmission shifts fine. What would cause that? Are you saying implying like a burnt clutch smell? Trans was supposedly rebuilt by a PO. Has a stall and a shift kit. Case looks clean.
If oil is burning on a Exh pipe it will leave a stain.What I am saying about a Transmm. is that ONE time I had a bad tranns. smell bad. If Your is working ok then that isn't it . Just smelling burnt oil don't mean it is dripping on exh pipe,, most oil from running engine will smell burnt, Smell can be coming from anywhere
 
Last edited:

79dentside

Full Access Member
Joined
Nov 20, 2019
Posts
369
Reaction score
383
Location
Kansas
First Name
Brandon
Truck Year
1979
Truck Model
GMC Sierra Classic
Engine Size
350
Another bit, I tuned up the motor and let it idle maybe 30-40 min outside. I wrapped the motor up a hand full of times as I was tuning the carb. I did see a puddle of fresh oil afterwards on the drivers side. Maybe the size of a softball. My suspicion is that in idle, it doesn’t blow back onto the exhaust, under load going down the road it blows all over the header and exhaust. Just can’t pin point it.
 

rusted nuts

Full Access Member
Joined
Mar 5, 2023
Posts
809
Reaction score
1,418
Location
Pa.
First Name
Jeffrey
Truck Year
1979
Truck Model
k20
Engine Size
4cly diesel
Another bit, I tuned up the motor and let it idle maybe 30-40 min outside. I wrapped the motor up a hand full of times as I was tuning the carb. I did see a puddle of fresh oil afterwards on the drivers side. Maybe the size of a softball. My suspicion is that in idle, it doesn’t blow back onto the exhaust, under load going down the road it blows all over the header and exhaust. Just can’t pin point it. then trace oil back to leak.
 

PrairieDrifter

Full Access Member
Joined
Dec 28, 2014
Posts
3,463
Reaction score
4,577
Location
North Dakota
First Name
Mason
Truck Year
84,79,77,70,48
Truck Model
Suburban k10, bonanza k10, c30 C&C, c10, gmc 1/2ton
Engine Size
350, 350, 350, 350, 350
If there's that much on the ground in that short time surely it is visible. You just need to really get in there. Above the oil filter, back and front of intake, pcv grommets, valve covers. Also it is likely to be blown backwards as well, due to the fan and while driving, front main and timing cover seals could be it. You have to clean very good then check for leaks.
 

Latest posts

Forum statistics

Threads
42,136
Posts
909,933
Members
33,636
Latest member
ehef
Top