High Oil Consumption after Rebuild 4.3L Merc.

[tomdcat]

The engine is a 4.3L mercruiser 1989 vintage with carburetor. I believe the ring where installed properly. However, I am still getting excessive oil consumption at high RPMs (>2500). I suspected the rings until I checked the Positive Crankcase Ventilation System by removing the breather and associated hoses to the valve covers. I ran for 45 mins. at both high RPMs and low?and no oil burn (too low to notice). Concurrent, I added a half of treatment of oil thickener.


Also, the oil pressure consistently stays at 80 psi while cold and between 70-80 psi when warm. Anytime it runs over 2000 rpm the meter is pegged. The upper read out limit is 80 psi but pegs about a half in further. My understanding is this is pretty normal.


I do suspect a clogged positive crankcase ventilation system. However, I do not know where the valve associated is or what exactly I need to do.

Any suggestions?

 

[Don S]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Have you ever rebuilt an engine before? Did you hone the cylinders to the proper cross hatch? Did you have the ring gaps in the proper locations per the manual? Did you plastigauge the bearings? All of them? What exactly is the oil consumpthion in question?
There isn't a PCV system on most marine engines.

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Thanks for reply.

No but had expert helping...Yes we used plastigauge and had to go oversized.

They manual I am using for my engine states clogged PCV system and first reason for high oil consumption....I am little confused with what this means

1) bored 30 over....used summit racing brand parts
2) Yes honed
3) complete new valve job and heads were resurfaced, all new seals and gaskets
4) ~15-20 hours on rebuild
5) oil consumption with breather depending on driving (high RPMs) up to 1 quart an hour of drive....however it appear w/o breather no oil consumption..haven't tested this on water and afraid to for safety reasons
6) using straight 30 weight...decent brand....I believe Pennzoil...but I have tried others

 

[Don S]

Re: High Oil Consumption after Rebuild 4.3L Merc.

however it appear w/o breather no oil consumption..haven't tested this on water and afraid to for safety reasons

15 to 20 hours on rebuild, and you haven't had it in the water and under a load??????? That's not good. How have you been running it?

However, I am still getting excessive oil consumption at high RPMs (>2500).

Exactly what manual are you using for this marine engine?

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Sorry for the confusion I have ~15 hours on water. about ~5 hours testing in driveway with garden hose.

I am reading the SELCO Mercruiser 1964-81 Repair Manual "Stern Drives" Section 3-11 titled EXCESSIVE OIL CONSUMPTION

Attached is some pix of the components.

 

[Coors]

Re: High Oil Consumption after Rebuild 4.3L Merc.

#1 toss the selco, and get a factory manual.
#2 A boat has no pcv
#3 If taking off the hoses helps; the rings ain't seated
#4 5 hours break-in in driveway... no good; Cam wasn't splashed good, rings need variable load, etc.

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.

I broke the engine in with muffs. 30 mins at idle then 30 mins at 1500 rpms then back to idle then 30 mins at 2000 rpms then back to idle...etc. I do recall seeing little vapor coming from valve covers but not much. I didn't run 3500 rpms with the first 5 hours of break-in.

 

[Don S]

Re: High Oil Consumption after Rebuild 4.3L Merc.

The first 30 minutes of an engines life should NOT be at idle, nor should the first 5 hours be without a load.
Sure you should start and engine and idle for a bit to set timing and adjust the carb, but it should be above idle (around 12 to 1500 rpm) for warm up and leak checks. Then is should hit the water for under load breakin. The cam is probably fine, but the rings never will seat.

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Don do you think is glazed?

Have you hear of BonAmi thru the carb to address glazed cylinders?

As if you can't tell, I am getting little desperate. And really don't want to pull engine.

 

[fishrdan]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Are those aftermarket valve covers, do they have oil baffles in the breather holes? Remove the breather hoses from the valve covers and look for rocker arms, if you can see rocker arms they don't have baffles and will lead to excessive oil consumption.

I had this problem with a set of aluminum aftermarket valve covers, the carb would suck oil droplets that passed by the breather (PVC valve in my case) and made me think I had a serious engine problem, when it was the valve covers causing the high oil consumption.

Another question, did you install a high volume oil pump and was the low pressure bypass spring installed (they normally come with the high pressure spring installed from the factory). 80PSi at idle and a pegged gauge leads me to think it's a high volume pump with the high pressure spring installed. Since the oil pump is driven by the distributor, excessive resistance from the oil pump can cause the distributor and cam gears to wear excessively I had this happen on an engine I built, cam MFG said I needed the low pressure spring in the high volume oil pump. This also happened to my neighbor on his 383 stroker, went through 5-6 distributor gears until he installed the low pressure bypass spring, along with replacing the cam...

 

[fishmen111]

Re: High Oil Consumption after Rebuild 4.3L Merc.

You did put in 30 over pistons and rings, right? The ring gaps were measured and staggered, correct? If so, I agree that you have probably glazed the walls from improper break-in. BonAmi trick can work, but can also fix your pressure issue by trashing your bearings. If you have a hp/hv oil pump without a larger capacity oil pan, get it out of there. Did you go oversize on your bearings? If so, was the crank turned, or did you use the 0.0001 over "backyard rebuild" bearings?

 

[chiefalen]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Brain on vacation when posted. Due to new meds.

 

[Coors]

Re: High Oil Consumption after Rebuild 4.3L Merc.

valve seats not machined correctly.

WHAT?

 

[bomar76]

Re: High Oil Consumption after Rebuild 4.3L Merc.

valve seats not machined correctly.

Of all the things under the sun it could be, this is absoulutely NOT one of them.

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Fishrdan these are fairly inexpensive aftermarket valve covers. Could I test this theory by sending the hose exhause on valve cover to collection point? Or would the oil just be burn.

The cam was polish and miced.....we used over sized bearings per shops suggestion. Cylinders were homed and rings were staggered correctly. I do suspect oil pump is source of problem (HV-HF). But if I need to pull engine to repace it with standard...I probably just need to go ahead with new set of rings and homed again the cylinder walls.

I just hate to do all this turn out it's just valve covers or something like this.

 

[Don S]

Re: High Oil Consumption after Rebuild 4.3L Merc.

I think you really need to plastigauge all your rod and main bearings while you have it apart. Don't ever assume just throwing in oversize bearings will work. You need to have the proper sized gap. To little will cause high oil pressure and less lubrication. Usually ends in spun bearings and blown engines.

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.



I setup test...I duct tape two aluminum cans with large holes to catch any oil spray. I should catch anything that is being shot out of valve cover.

 

[bomar76]

Re: High Oil Consumption after Rebuild 4.3L Merc.

Never use a High Volume oil pump in a marine engine with a stock pan...they can suck up oil out of the pan faster than it can recover.

Have you actually put a temporary mechanical oil pressure gauge on it?
It sounds as if you could have the wrong sender.

How about performaing a compression and leakdown test

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.

http://www.hotrodders.com/forum/high-oil-consumption-aftermarket-valve-covers-137568.html

 

[tomdcat]

Re: High Oil Consumption after Rebuild 4.3L Merc.

bomar, I have the equipment to do compression test but don't see the point since I am only getting oil consumption at high RPMs or under load. I feel like leak test in driveway will not offer any insight to the problem.