Let's talk oil loss

[Captainblastem]

Hello everyone,
I have a 1990 with about 93k miles. I did the 60k myself(because I didn't trust the previous owner's word). Everything looks and runs as you'd expect after a 60k except...

I got on the gas one particular time, and I noticed a cloud of blue smoke from the exhaust >:| So.....I'm going to do a compression test and check the condition of the spark plugs. I suppose my question to you all would be, is the yamaha V6 known for:

- excess blow by
- leaky valve seals
- rings going bad before 100k miles
- a PVC system that tends to suck everything out of the crank case like a hoover vacuum cleaner. The PVC hose that goes to the vacuum side of the throttle body is rather huge and the entire intake system is coated in sludgy oil.

I bought this car off the original owner, who is an old lady at this time, so I don't know how often the car has been raced, if at all. Any insight would help, because I'm considering buying another SHO engine, and completely rebuilding it and dropping it in. Also, anyone know what the PSI range of the compression test should be? I have a complete shop manual for the '89 and '90 and they are both somewhat useless when it comes to some specific information.
- Rob

 

[msteiny]

The PCV system is not the best. So when you got on it, it probably sucked a bunch of oil sitting in the intake manifold. If you get on it more often, like it is meant to be drivin the smoke will go away eventually.

 

[luigisho]

Mine uses more oil than I would like at 117k. I open it up frequently and notice oil in the exhaust. Going to look at valve stem seals and rings in the spring/summer. Oil use is not uncommon on these motors. Neither are leaky seals at the crank, valve cover and cam shaft.

 

[Captainblastem]

Hmmmm well I know my valve cover gaskets are squeaky clean. The cam seals are all good as well. Not sure about the crank seals. It looks like the oil pan is coated in oil, so who knows. It could be leaking at the tranny.
If these engines are known for losing a bit of oil, then that's a bit of a relief. I'm still going to check the compression though. Do you happen to know what the compression psi range should be ?

 

[tommyturbo]

All three of my cars will use oil, leak oil, and burn off some when driven in a spirited way. I've read that the oil control rings tend to get carbon build up which may also contribute to the oil in the exhaust. I just accept it as a SHO thing, and check the oil regularly and enjoy them.

 

[rubydist]

the SHO motor is known for more or less all of the stuff you listed.

the rings are low-tension, so they don't "go bad" but they do get stuck. This is more likely if the little old lady drove it, because she probably only drove it to church (which is why a 20 year old car has only 90k) and it didn't get warmed up enough, or driven hard enough to not get all carboned up. Often, one can pull the rings (carefully), clean them and the ring grooves all up and reinstall the factory rings with success.

the valve stem seals (especially on the exhaust valves) are going to be bad after 20 years and 90k miles, but they don't burn a whole lot of oil even with missing valve seals, because the valve actuator cap comes down past where the seal sits, so not a whole lot of oil is flying around at the top end of the valve. None of the SHO motors I have had apart had any problems with valve guides.

the pcv system really needs a remote catch can to separate the oil from the flow.

having said all that, let me address your symptoms. Blue smoke when you mash on the gas is likely to be from bad/stuck rings. Blue smoke when you lift off the gas at higher rpms is likely to be from valve seals/guides.

 

[Bryan]

I get blue smoke to sometimes, but only when the car first starts after sitting overnight. After a little driving it goes away and she runs normally with no problems. She does use a little oil, but after 20 years of on the road driving I'd expect as much.

 

[rubydist]

blue smoke in the morning after sitting overnight is generally attributed to bad valve stem seals.

 

[Bryan]

blue smoke in the morning after sitting overnight is generally attributed to bad valve stem seals.

Yeah figured as much, but since in a earlier post you made it seem like its not a major issue. So I'll just keep the oil topped off and run her till I can get her fixed right.

 

[1badsho]

As much as I know these cars you learn something every day. My oil consumption on an original 76k motor is higher than what I would have guessed. Especially when you take into consideration that I replaced every possible rubber seal in this motor when I rebuilt it myself.
I notice more consumption at hwy speed .... vs lower rpms .... around town its not bad just when u get on the interstate ....at a constant 65mph no a.c .... 30 mpg

dond

 

[SHOdded]

What oil do you use, dond?

 

[jimtash]

As much as I know these cars you learn something every day. My oil consumption on an original 76k motor is higher than what I would have guessed. Especially when you take into consideration that I replaced every possible rubber seal in this motor when I rebuilt it myself.
I notice more consumption at hwy speed .... vs lower rpms .... around town its not bad just when u get on the interstate ....at a constant 65mph no a.c .... 30 mpg

dond

The old engine in my SHO consumed the most oil at constant highway cruise as well.

 

[1badsho]

I use 10/30

 

[SHOdded]

I wonder what sdpatt has to say about this. He successfully runs Castrol GTX 10W30 on a very high mileage engine.

 

[Bryan]

Right now I use 5w 20. In the summer I switch over to 5w 30. Should I be using a heavier weight?

 

[SHOdded]

If you are on conventional oil, you should be fine, though 5w30 year-round is a no-brainer as well. 10W30 is used down south just because the temps don't get as low as often as they do in our area. IDK if switching to 0W30 (or 0W20) in these "polar" winters may help a little bit during startup. A heavier weight oil helps the bearings from getting oil starved. Hence my decision to stick with 5W30 even during winter time.

 

[rubydist]

I would not use a 5W20 in the SHO motor.

Keep in mind that the first number "5W" tells you the viscosity of the oil when the oil is cold. The second number "20" tells you the viscosity of the oil when it is warm. There is no advantage to using a "10W" oil rather than a "5W" or a "0W" oil in any motor. All you get from the "10W" oil is thicker goo when the oil is cold. There is never an advantage to that. The warm viscosity number for the SHO motor should always be a "30" unless you know you have loose bearings, in which case a "40" would be safer.

In a plain bearing (the type that engines use for main and rod bearings) a film of oil is required to keep the two metal parts from touching each other - if that oil film breaks down in the SHO motor the result is spun rod bearings. The ideal viscosity of oil to form that oil film is a function of the bearing clearance, the volume and pressure of oil supply, and the temperature at which the oil and metal parts operate. If the oil is too thin, too much of the oil "leaks" out the sides of the bearings such that there is not a sufficient supply of oil and pressure at the last bearing in the circuit. If the oil is too viscous, then the pressure required to pump it through the system goes up, and a significant portion of the oil pump output is bypassed by the pressure relief in the pump, and the result is again not enough oil supply and pressure at the last bearing in the circuit. So, the proper viscosity is a balancing act. It turns out the factory engineers knew what they were doing when they specified 5W30 oil. in the past 20 years, oil refining has been improved, and 0W30 oil is available, which is even better.

So, if the bearings are at the high side of the tolerance (and knowing the SHO motor's tendency for rod bearing issues) then going to a 0W40 or 5W40 oil would be safer because that increased viscosity at temperature would help control the oil leakage from the sides of the bearings and therefore help ensure a satisfactory supply of oil and pressure throughout the oil system.

Oil at room temperature is much higher viscosity than oil at operating temperature, so using a "0W" oil is always a good idea, no matter if summer or winter, because what that does is provide a oil viscosity at startup that is closer to the operating temperature viscosity that the engine was designed for.

 

[1badsho]

so a perfect oil say for my 20 yr old 80k motor would be 5-40 ?

 

[rubydist]

I would run 5W30 unless I had a problem (like an occasional oil light flicker when hot) that suggested oil pressure was low with that.

Out of all the SHOs I have owned, I only had one that I used 5W40 in because it apparently had looser bearings and I would occasionally get an oil light flicker at idle on a hot day with 5W30. It ran fine with 5W40.

Keep in mind that lighter oil provides lower pumping losses so you lose output power by going to a heavier oil. So you only want to go heavier if you have a real reason to do so.

 

[1badsho]

RUBY .... ARENT U THE ONE WHO BOUGHT ALL MY SHIMS WHEN I GOT OUT OF THE sho BUSINESS lmao ,,,,YA right