7.4 MerCruiser Oil Capacity

[Freeebird]

I've been questioning this for years and finally broke down and called Mercury this morning. I've owned a number of boats with 7.4/454 engines, and the owner's manuals say 7 quarts which is also the case with Chevy trucks I've owned. The Chevy's always came to the full mark on the stick after adding 7 quarts. Problem is, 5 quarts is what it takes to bring the oil level to full on a MerCruiser. This has been the case on every one I've ever owned, including the ones in my 41. Yes, it's oil time change again, and it's got me to thinking... again.

The guy I talked to told me the specs did in fact call for 7 quarts, but then he went on to say that I should go by the dipstick. This despite the fact he confirmed there was never a 5 quart oil pan installed on a 7.4. That advice seemed to be somewhat contradictory to say the least. He then went on to say that measurements are approximate, and that there will always be some residual oil left in the pan after an oil change. Sorry, but not two quarts.

All things being equal, I'd rather be two quarts low than two quarts too much, so I guess I'll keep using the stick. That being said, I would sure like to know why the numbers don't add up.

[Bob Bradley]

Probably because its a Mercruiser and not a Crusader.

[MikeP]

"All things being equal, I'd rather be two quarts low than two quarts too much, so I guess I'll keep using the stick. That being said, I would sure like to know why the numbers don't add up."

Totally agree. In addition to oil consumption issues with overfilling, too much oil can become not enough oil due to crankcase windage. Mopar did a test many years ago that showed that a 426 hemi motor without a windage tray but NOT overfilled could wrap 5 quarts of oil around the crankshaft at 7k+ RPM in a sort of "tornado foam" of oil which basically took 5 quarts of oil away from what was available in the pan for engine lubrication. I don't know if the Mercs have windage trays but overfilling can cause the problem because it raises the oil level too close to the crankcase or may even cause the crank to dip into the oil…and turn it all to froth.

[drburke]

I think the pans on a Cummins 6B are shallower on the marine vs. road engines, the issue being installed height.

Is it possible they *did* use a shorter 5 quart pan but the difference in capacity is residual oil in the coolers/heat exchangers and lines?

Just wondering...

DAN

[Freeebird]

Not sure why it would matter Crusader vs MerCruiser as it's still a GM engine.

I got the feeling the Mercury guy was just reading from the same manual I have as to capacity. One thing he did ask was if I had measured the amount of oil I took out of the engine. I answered no, but it's pretty obvious if I drain the oil and put 5 quarts in, 5 quarts is the most that can come out. Not sure where he was going with that.

[thoward]

5 quarts includes refill of oil filter?

[Freeebird]

Yep, that includes the filter.

[MikeP]

FWIW, 5 quarts with filter was a pretty common figure for standard US V8s back in the day with an oem oil pan so it seems like a pretty good number for the same motor assuming the marine version doesn't have a larger oil pan. Pics I have seen of mercs and the actual Crusaders I have owned had the same pans as the car versions.

[34Hatt]

Problem with dipsticks and quantity of oil is also dependent on Angle of motor in boats !

[Freeebird]

Problem with dipsticks and quantity of oil is also dependent on Angle of motor in boats !
Two quarts worth of variation on the stick? I don't think so. Besides, mine set at almost a zero angle. The MercCruiser guy said they never made five quart pans for a 7.4, and I've never seen an automotive five quart pan either. Besides that, as I said earlier, I've owned other boats with 7.4's and had the same issue. With that, I can't be the only one who has ever asked this question. Somebody somewhere has to have the answer.

[dottieshusband]

Randy, I've had both the 7.4 and 8.1. (454/496) They both took close to 8 quarts with filter. Are you sure you are getting it fully drained? On the 7.4, I used a manual pump that screwed to the dip stick holder. The 8.1 had an oil exchanger on the pan drain plug.

[Freeebird]

Paul, I'm sure I'm getting all the old oil out. I always get the engines hot, and there's only so many ways to suck oil through a dipstick tube. Like I said, I had the same experience with other boats with the same engine.

That being said, I did use a different method this time since my dedicated 12V oil change pump didn't wanna play. I have an oil change container with a built in pump which worked much better (faster) than I expected never having used it before. Several pumps pressurized the tank and quickly sucked all the oil out of the pan like magic. I'll be refilling tomorrow, so we'll see.

[dottieshusband]

Capacity changes through the years, both my 454 and 496 were 2001+ just be glad it's not 10 Gallons, and another 9 for the tranny!

[Freeebird]

Been there, done that, and I AM glad!

Once again, both engines showed full at five quarts. Go figure. Oh well, I've never had any problems with 7.4's and five quarts, so I'll just keep doing what I've always done.

[roundIII]

Just did my 1988 454 Crusaders yesterday. Original motors on a 40' MY. 6 quarts with filters. Right to the full line.

RR

[34Hatt]

Surprised no one asked are they steel pans or Aluminum? Pretty sure all the aluminum ones are 6 quarts or more.

Some good pictures and measurements someone like Dave could tell by looking at it?

The angle can make a 1 quart difference plus you never get it all out, unless you pull the plug it adds up but you said yours are level so it does not apply here. I would figure maybe 1/2 quart left behind so yours look like maybe 5.5 quarts seems a little short for a marine application.

My 330 Bs are pretty level and I get an extra 2 quarts out by pulling the front plug but its a longer pan.

[Boatsb]

Been there, done that, and I AM glad!

Once again, both engines showed full at five quarts. Go figure. Oh well, I've never had any problems with 7.4's and five quarts, so I'll just keep doing what I've always done.

Stop bitching. You saved $15 a side. That's something to be proud of here.

[krush]

It may be more than 5. You have an oil cooler that holds some oil. Also, the dipstick tube that you suck through may not go all the way to the bottom of the pan. Pull the plug next time and see if more comes out!

I'm seem to recall my 454 mercruisers only take around 5-6. I use diesel oil.

[lake of the woods]

Since we are talking about oil and gas engines I would like to ask what oil / filters (brand / older engine oil, synthetic, etch) some of you use for your gas engines.

I have 1989 454 crusader engines that start and run very well with less than 700 original hours each. It has been a fresh water boat since birth. I have been using Shell Rotella triple protection for the last few years but have been considering going to Rotella 6T synthetic. What do you think? I aloe just use a Fram regular oil filter. Should I use one of there filters that claim to provide more protection?

[Freeebird]

Stop bitching. You saved $15 a side. That's something to be proud of here.Who on here is paying $7.50 per quart for oil? :D

[Freeebird]

Since we are talking about oil and gas engines I would like to ask what oil / filters (brand / older engine oil, synthetic, etch) some of you use for your gas engines.

I have 1989 454 crusader engines that start and run very well with less than 700 original hours each. It has been a fresh water boat since birth. I have been using Shell Rotella triple protection for the last few years but have been considering going to Rotella 6T synthetic. What do you think? I aloe just use a Fram regular oil filter. Should I use one of there filters that claim to provide more protection?I've always used MerCruiser filters and MerCruiser oil just because that's what it's always had in it. I'm sure other oils and Fram filters would work fine, but when you're only doing one oil change a year, why take any chances?

That being said, I've used Mobil 1 synthetic in the cars/trucks I've owned over the years and have put well over 100K miles on several with no problems whatsoever. Not sure why, but I've had a number of people advise against using it in marine applications.

[Freeebird]

It may be more than 5. You have an oil cooler that holds some oil. Also, the dipstick tube that you suck through may not go all the way to the bottom of the pan. Pull the plug next time and see if more comes out!

I'm seem to recall my 454 mercruisers only take around 5-6. I use diesel oil.The dipsticks go all the way to the bottom of the pan, and I doubt very seriously it would make any difference to drain the oil through the pan plug vs the dipstick tube. They are specifically designed to pump oil through and even have threaded fittings at the top of the dipstick. Getting to the pan plug and not making a huge mess would be almost impossible.

[krush]

Since we are talking about oil and gas engines I would like to ask what oil / filters (brand / older engine oil, synthetic, etch) some of you use for your gas engines.

The only "worry" is that these engines are flat tappet lifters. I say "worry" because internet nerds seem to go nuts saying modern engine oils don't have zinc, etc blah blah and it wipes the lobes on flat tappet cams.

Does this really happen? I don't know. But Diesel oil should take care of this problem...or toss in some STP or whatever.

[Boatsb]

The only "worry" is that these engines are flat tappet lifters. I say "worry" because internet nerds seem to go nuts saying modern engine oils don't have zinc, etc blah blah and it wipes the lobes on flat tappet cams.

Does this really happen? I don't know. But Diesel oil should take care of this problem...or toss in some STP or whatever.

Valvoline blue. Plenty of sink for the Cummins so I'd say it's a good choice for gas engines.

[krush]

Valvoline blue. Plenty of sink for the Cummins so I'd say it's a good choice for gas engines.

I've been using Rotella T6 synthetic.