bago Baja

Hi all,

I've read several threads elsewhere about oil consumption in big block chevy marine engines. The discussions have all centered around 454 mags and 502's. The consensus seems to be that these engines often use a bit of oil, especially under hard throttle. I've read that these engines have forged vs cast pistons and different oil rings resulting in the oil consumption. Many posters have indicated a quart of oil usage every 4 - 15 hours.

I have a stock 1988 7.4 liter / 330 HP motor with ~ 650 hours that burns a quart every 6 - 10 hours depending on how hard I push it. I'm running straight 40 wt. non synthetic oil. No smoke or soot and runs great.

I run ~ 4200 rpms at WOT, should be 4600 so I'm lugging it a bit. Not sure if this could be involved in oil consumption or not.

I just bought the boat (Baja Force 235) last spring and when I changed the oil I could only get 5 quarts out. Took it to the shop and had them change oil. They could only get 5 quarts out. Mechanic said it should be 7 for sure. They put 7 back in and told me to mark the stick in the water. Mark is 2" higher than before. No aeration or other problems with the higher oil level. Dip stick number checked out OK. Maybe running low oil level caused consumption problem?

Comments and advice welcome.

Tom

mopower

2 , 1989 , 330/454 Last season 57 hours and just over 1100 mile (gps) and each engine used a quart and a half and that's with 720 hours on the clock. Most of it was 3000 to 3500 rpm range aside no wake zones. Top rpms...46/4700 , so no lugging here

blue thunder

I believe you have cast pistons, so that should not be an issue. I would be wary of the 7 qts in the pan. Watch oil pressure like a hawk at WOT to see if it starts dropping. I personally would put it back to the line on the dipstick.. this would not cause oil consumption.

4200 is way too low. I'd reprop to spin the engine at about 4800rpm. This will be three inches in pitch and should make your engine run better. I think this will help your consumption problem, but not sure. The other thought is if hasn't had a valve job, it is probably time. Could be loosing a little oil around the valve seals. Also, you may make more power after this resulting in a better WOT rpm. I usually do vavle job at 500 hrs max. This will also give you an opportunity to service the exhaust system.

BT

bago Baja

Thanks for the feedback mopower and blue thunder,

I just sent my prop (Mirage 23P) to Houston Propeller in exchange for a labbed 21P (plus a few bucks of course). I told Darin I wanted to be up tp 4600 rpm. The book says thats max on this engine. Different than 454 mag.

I still think there's a problem with the stick or tube. I found out about my oil consumption problem this summer after not checking oil level for too long (won't do that again!). Oil pressure dropped to ~20 psi. Checked the dip stick and just the tip had oil on it. Idled back to the dock with pressure at 10 - 20 psi (I carry spare oil now!). No noise from the engine during the whole episode so I don't think any damage was done. Funny thing was, 2 quarts brought it back to full on the dip stick. When I changed the oil, only 5 quarts came out.

Doesn't seem like two quarts down on a 7 quart oil pan should result in low oil pressure. What do you guys think?

Tom

DJRITTER

Lower than normal oil level won't necessarily result in a low oil pressure reading. Of course, if the oil level ddrops to the point where the pickup is uncovered you might see the pressure fluctuate. Low oil level can cause a higher-than-normal oil temp, which could give a lower than normal pressure reading after returning to a no-wake speed after a hard run.

mopower

Bago B,
If I run mine up @ 38/4000 for a while my oil pressure will drop a little too and @ idle have about 20 lbs. Leave it idle for a few minutes and it's back to 35/40 at and idle and 50/55 at speed.
It's just the oil getting hotter..

bago Baja

Thanks again guys,

The day I found out that I was 2 quarts low and had 20 psi oil pressure, it was at ~ 3200 rpm. I was cruising along and looked down at the the oil pressure guage and couldn't believe that it was bouncing around 20 psi. It normally ran ~ 55 or so at that rpm. I'm pretty sure that the oil pump was sucking air at that point. When I shut down and checked the dip stick, just the tip had oil on it. Started back up and idled home with pressure bouncing between 10 and 20 psi. I'm convinced that the stick or tube are screwed up. I haven't run it enough with the higher oil level (7 quarts) to see if oil usage is better or not.

I probably need to run compression checks on the engine. blue thunder may be right about the the valve job. If I go that far I may think about some modifications to increase HP.

Tom

Montauk Crossbow

Bago, I also have 1988 330'swith 200hrs as of this season,I don't burn any oil, and upon oil change,I only use 5 quarts ,I'd be weary of adding 7 Good luck

bago Baja

Thank you all for your comments. It's great to be able to get feedback like this. Everyone seems to be telling me to be careful about adding the 7 quarts. I'll have to re-evaulate this situation next spring and decide what to do.
Thanks again
Tom

mopower

Yeah 'Bago,
7 qts is an initial fill up and the total that it holds. You never get everything out when you drain them.
I'm doing new engines in the spring with 9 qt pans , 2 qt filters , plus hp500 style cooler and lines. This will probably wind up at 12-121/2 quarts on initial fill. After that maybe 11qts for a change