Rebuilt 7.4 Mercruiser losing oil??

[12guns]

Only have 10 or so hours on a rebuilt 454 in a 24' Arriva. Runs GREAT, strong as always. Today I heard the engine sounding a touch "off". I raised the engine cover and could hear the valve noise, just ever so slightly louder than normal. Engine was running cool as it should, but the oil level was low. Not sure how low, cause it was not touching the dip stick....Bad, I know. So I loaded it up and have been wondering where that oil has gone. I changed the oil filter a couple weeks ago, but didn't think there was enough oil in the used filter to make the level drop.
There is no excess oil in the engine bay, just misc fluids from the years of use. So where else could the oil go?
Have I caused any damage by running slightly low on oil? Like I mentioned, even w/ low oil, it was not getting hot and was still pulling strong, so I hope adding oil will cure my problems.
The owner of the boat said there something in the oil/water cooling system that can leak, causing oil to be blown out with the exhaust...Can you explain further? I don't recall any smoking from the engine or exhaust, just need to track down my leak and make sure she's ready for the summer! Thanks for any help!!

 

[Pete104]

Re: Rebuilt 7.4 Mercruiser losing oil??

He was refering to engine oil cooler. Who rebuilt the motor? Who didn't check/replace the oil cooler?

 

[12guns]

Re: Rebuilt 7.4 Mercruiser losing oil??

A guy named Roger Carter in Heber Springs, AR. Great mechanic, been doing it all his life. I'll have to ask if he replaced the oil cooler. Would it be clogged up? Worn through holes leaking into the water system? Where is the oil cooler located, and is it an easy repair? I've done starters, oil changes, and such, just not sure how big of a job I'm looking at.

 

[Pete104]

Re: Rebuilt 7.4 Mercruiser losing oil??

If it's not going into the bilge, it must be entering the cooling system water. The oil is under pressure where the water isn't. I have no idea which 454 you have, it's usually located port side under the motor mount. It's a combination engine oil/ power steering fluid cooler. Rule number 1 never use a used oil cooler with a fresh motor! I think you would know, it's roughly 500 bucks.

 

[12guns]

Re: Rebuilt 7.4 Mercruiser losing oil??

I have no idea if there is a used oil cooler in it or not, but I'll find out tomorrow when I call the mechanic. I would give you more info on the motor, but it's been worked on so much I'm not sure it's all original anyway. It's on an 89' Arriva, but that's about all I can tell you. I'll have to clean and check the bilge again too, need to make sure it's not just a leak. Thanks for the replies. Sounds like if it's not a simple leak, I can check the oil for water when I change it. That may tell me if the heat exchanger has a leak?

 

[12guns]

Re: Rebuilt 7.4 Mercruiser losing oil??

Any other thoughts about losing oil? It will be a couple weeks, but I'll change the oil/filter and see if there's any water in it. Other than a leak, anywhere else the oil could have gone??

 

[joncrisler]

Re: Rebuilt 7.4 Mercruiser losing oil??

new or newly rebuilt engines tend to use more oil, but it sounds like you are down at least 2 quarts over 10 hours- that is too much. The engine could be burning the oil, if so its going out the exhaust. Can you run it on muffs and check the exhaust for the tell-tale blue smoke ? I would recommend a compression test as well.

 

[OldNBold51]

Re: Rebuilt 7.4 Mercruiser losing oil??

new or newly rebuilt engines tend to use more oil, but it sounds like you are down at least 2 quarts over 10 hours- that is too much. The engine could be burning the oil, if so its going out the exhaust. Can you run it on muffs and check the exhaust for the tell-tale blue smoke ? I would recommend a compression test as well.

+1. 454 use some oil but 2 qts in 10 hrs is high. I've 20 hrs on my rebuild and I've used 1/2 qt. I've found wfo throttle will use more by quite a bit. Fact is, my usage came after a 35 minute wfo throttle trip at the 18 hr mark. No usage prior to that with normal rev's of 2600-3000.

 

[boat1010]

Re: Rebuilt 7.4 Mercruiser losing oil??

If you changed the filter you have lost just about a quart of oil depending on which filter you use. How much oil did it take to get back on the full mark? Was the boat sitting level when you checked the oil? I have a 89 Arriva and just had the motor replaced. Like oldNbold said I would have a compression check done and have the mechanic that worked on it look it over. There should be some sort of warranty.

 

[12guns]

Re: Rebuilt 7.4 Mercruiser losing oil??

I'll look into it. We'll be changing the oil next weekend, so I'll see if there is any leakage. It was running cool and strong (52+ mph w/ SS prop) right before I realized the oil was low. If there's no water in the oil, I'll assume the cooler is not cracked. I'll watch for smoke, but I'm 90% sure it's not burning enough oil to see any smoke.
I hate to admit it, but I didn't check the oil after replacing the filter. I did not think it held enough oil to matter. Guess I was wrong there. Thanks for all the replies, and don't beat me up too bad...
So between the newly rebuilt motor, and the filter change, I'll hope that is the cause for low oil. The mechanic will help track down the leak if there is one, just don't want to have to take it back if It's something I can do. He's a good guy but he's busy. Rest assured, if there's a major problem, he'll get it back, just prefer to do it myself. Thanks again for all the help.l

 

[OldNBold51]

Re: Rebuilt 7.4 Mercruiser losing oil??

A boat mechanic i know stated he can't stand the 7.4L's as they use oil and the owners are too lazy/stupid.....whatever.... to check the dipstick. He's replaced many big blocks due to them running out of oil. I quizzed him as to where the oil is going and he couldn't really put a finger on a cause but he made the blanket statement "they all seem to use oil, some more than others". I asked if it were the rings and break in procedure and he really couldn't blame anything.....but he did say what seems to work best for them is the "hard" break in procedure. He stated that every boat he's rebuilt that the owners babied the initial break in were using oil.

 

[HT32BSX115]

Re: Rebuilt 7.4 Mercruiser losing oil??

A boat mechanic i know stated he can't stand the 7.4L's as they use oil and the owners are too lazy/stupid.....whatever.... to check the dipstick.

Mine doesn't use oil..........Just because he calls himself a "Boat Mechanic".......doesn't make him a competent one.......

but he did say what seems to work best for them is the "hard" break in procedure.

Strangely enough, he got that part right!

If there's no water in the oil, I'll assume the cooler is not cracked.

DO NOT make that assumption.

There's little or no water pressure when the engine is not running.....and not a lot of pressure when it is................but 40 PSI or more engine oil pressure when it is running.......you could absolutely have an oil leak into the cooling system water through the oil cooler.

I would remove the oil cooler, get some fittings and pressure it up to about 50 (air) psi and hold it under water..........look for bubbles.


Regards,


Rick

 

[12guns]

Re: Rebuilt 7.4 Mercruiser losing oil??

Great advice. I'll check it when I change the oil next week.

I've read ALOT of info on "hard" break in's. I'm sold on it. However the mechanic my friend used is not. He's old school and since the boat is not mine, we broke it in by the book. It is comforting to know the 454's use oil. I don't have a problem checking the oil everytime we take it out. My friend (son of the boat owner) did not check it when he launched the boat or he would have seen that it was low.
Thanks again, great tips. I'm hoping for no water in the oil and no leak in the cooler, but we'll see.

 

[joncrisler]

Re: Rebuilt 7.4 Mercruiser losing oil??

Does your filter sit upside down (so it might drain) or the traditional way? If upside down, then its hard to say how much oil was removed with a filter change. If allowed plenty of time to drain, it might only be 1/4 to 1/2 quart. If it sits the traditional way (opening faces up) then you could have easily lost 3/4 to more than 1 quart. Also, what weight oil are you using? I had a buddy with the same complaint with a 5.7, and it turned out he was using 5w30, which is a bit too light for boat engines. Switching to 20w50 brought oil consumption back to normal.
My 454's in my boats do not use any appreciable amount of oil in a season. I run a full synthetic 20w50. My Suburban 97 454 4x4 uses about 1 quart in 3k miles using synthetic 5w30.

 

[cr2k]

Re: Rebuilt 7.4 Mercruiser losing oil??

If the heads were not rebuilt it could be the valve guides.

 

[12guns]

Re: Rebuilt 7.4 Mercruiser losing oil??

Topped off the oil, pressure is back up to 55 at idle...I didn't run it up to temp b/c it was 10 pm here and I scared even myself when I started it up! Valve noise is gone. I'll run it on the lake tomorrow evening and make sure all is well and there's no water in the oil. Then to start on my list of "to do's"! Thanks for the help.

 

[12guns]

Re: Rebuilt 7.4 Mercruiser losing oil??

Ran the boat today, oil pressure back up to 60 and steady, 45 or so at idle. Looks like after messing w/ the temp sending unit, my temp gauge even works now! I checked the oil, still clean and water free. I'll keep a closer watch over it, but looks like all is well. Thanks for the help

 

[flipbro]

I just rebuilt a Mercruiser 454 Magnum 1998, and it is consuming a lot of oil, 1 quarter every hour. No smoke at the exhaust, no oil at the bilge. Oil pressure goes down to less than 30 psi when running.
Next week,as a first step, I will change the oil cooler, which is very old, and recheck oil again. If it does not work, as a second step I will perform a compression test, if OK, then I will check the the valve guide seals.

30 psi on a rebuilt engine? You've got bearing clearance issues.