Mercruiser 5.0 engine help for dummies

[Learning Still]

Firstly- yes, complete newb but not from lack of trying. Where I am, marine mechanics are hens teeth, and I am a first time boat owner learning on my own. I’ve repaired cars and RVs and gone through enough forums to know that dumb questions aren’t the best intro but yep, we are not full time boaters and what’s second nature to boaters is still not for us (my son brought the boat back with the plug in and when the cover collapsed I discovered we’d drowned the engine). So I’m not sure if anyone feels inclined to help, but even just pointing me in a starting direction would really be meaningful as I’m so tired of toys being ornamental.
Problem #1: 5.0l mercruiser engine not starting after winter, not sure what to check first.
Background: 5.0l engine was summer and winterised by a mechanic no longer in business, but had several outings in 2019, none in 2020. Batteries are charged.

Problem #2: 3.0l mercruiser engine not starting after winter, not sure what to check first.
Background: New engine in 2016 due crack, new engine never performed and frequently stalled on start up, despite many trips back to mechanic it continued to run rough with low power and stalled between 800-1000rpms. Mechanic finally said “well that’s what you get with a second hand engine…” It was a brand new engine, seller a reputable boat engine supplier, mechanic says out of the box looked like it was just in another boat. Lived in the shop 2016/17/18/19, then gave up. Now decorates the lawn.Bought the 5.0 for a trouble free experience but wasn’t able to sell the 3.0 in current condition.

Ive been warned about breaking things so don’t do any work on them at home, but decided that has to change.
Where would one start??

 

[Scott Danforth]

First, welcome aboard

Second, how were the engines winterized.... Be specific

Does the 5.0 turn over?

Does the 3.0 turn over?

 

[CaptnKingfisher]

Welcome. The day I started wrenching on my own engines was the day I found a new passion. I think I enjoy the maintenance as much as I enjoy the boating. Specially when it's not my boat I'm working on

My first recommendation is get yourself a service manual for each engine. A ton of good technical information and some really handy flowcharts for diagnosing different conditions. I highly recommend getting the service manual published by mercruiser. The manufacturers manuals are usually far better than clymer or seloc or whoever else makes those things.

I would suggest you get ahold of a good multimeter (I'd recommend buying one that is capable of measuring dwell and includes a tachometer, these two features come in handy and are not on a typical electricians multimeter), an adjustable spark tester (adjustable adds a whole other dimension to your ability to diagnose weak spark conditions), and a quality compression tester. These run close to $100 and not a tool you need to use everyday so you could loan one from your local autoparts store if youre not inclined to buying one. Don't buy the cheapest one on Amazon, read the reviews and you can get a decent one without paying a fortune.

With these three tools you can diagnose most engine problems by running a few simple tests. Basically any engine needs three things to start: compression, spark and fuel. So that's what you're going to test for.

Some simple tests I would start with, given the history of the boats: I'm going to bold terms that you can search on YouTube for an example of how to do this test.
1: fuel quality test. Get a clear glass jar and siphon some fuel out the tank. Make sure there's no water in your gas tank.
2: test for spark at each cylinder. adjustable spark test.
3: if spark is weak, or no spark, before hunting down issues in the ignition circuit id do a voltage drop test on the battery. Could just be a weak battery. If no spark, and battery good, post and we'll help you troubleshoot.
4: if spark is good (jumps 1/2" gap) and the fuel in the tank is good, next I'd do a compression test on each cylinder.
5: if compression is good, spark is good and fuel in the tank is good, then we can conclude we've got a fuel issue. I like to keep a can of fresh fuel around and at this point I try dripping a little fuel directly into the carburetor and cranking to see if that allows the engine to start. If it still won't start with fuel getting to the carburetor, strong spark and good compression then I know it's time to rebuild the carburetor. On the other hand, if dumping fuel into the carb allows the engine to start up (and then stall out when it runs out of fuel) then I know the carb is fine and it's a fuel delivery problem. So I clean the fuel filter, try again. If no improvement I suspect fuel pump needs to be replaced.


I skipped over what to do if you have a no spark condition or what to do if compression is bad. Mainly cuz I suspect thats not your problem. But if you do have bad compression or no spark post the results and we can guide you through troubleshooting. By the way when you're doing these tests and posting results, it's much easier to help when your specific about the results. We like data here. Good luck and welcome aboard

 

[Learning Still]

First, welcome aboard

Second, how were the engines winterized.... Be specific

Does the 5.0 turn over?

Does the 3.0 turn over?

* Whoops, bigger engine is 5.7L.

No details on winterising as he has since closed/relocated. But I did get a discount as the 5.7l was less labor intensive being a closed cooling system.

The 5.7l IS turning over and has fresh batteries (24 and 27)

I have the 3.0l battery charging at our local Napa.

Due not doing anything in 2020 only 1 of the 3 new 2018 batteries survived. *lesson learned. I can’t get power to them so I’ll be removing and storing on a trickle charger this winter inspire of how difficult it is for me to get them out/back in (mentioning in case someone like me is reading).

I have a SELOC Mercruiser Stern Drive 1992-00 Repair Manual that came with the 5.7l engine.

 

[Learning Still]

Welcome. The day I started wrenching on my own engines was the day I found a new passion. I think I enjoy the maintenance as much as I enjoy the boating. Specially when it's not my boat I'm working on

My first recommendation is get yourself a service manual for each engine. A ton of good technical information and some really handy flowcharts for diagnosing different conditions. I highly recommend getting the service manual published by mercruiser. The manufacturers manuals are usually far better than clymer or seloc or whoever else makes those things.

I would suggest you get ahold of a good multimeter (I'd recommend buying one that is capable of measuring dwell and includes a tachometer, these two features come in handy and are not on a typical electricians multimeter), an adjustable spark tester (adjustable adds a whole other dimension to your ability to diagnose weak spark conditions), and a quality compression tester. These run close to $100 and not a tool you need to use everyday so you could loan one from your local autoparts store if youre not inclined to buying one. Don't buy the cheapest one on Amazon, read the reviews and you can get a decent one without paying a fortune.

With these three tools you can diagnose most engine problems by running a few simple tests. Basically any engine needs three things to start: compression, spark and fuel. So that's what you're going to test for.

Some simple tests I would start with, given the history of the boats: I'm going to bold terms that you can search on YouTube for an example of how to do this test.
1: fuel quality test. Get a clear glass jar and siphon some fuel out the tank. Make sure there's no water in your gas tank.
2: test for spark at each cylinder. adjustable spark test.
3: if spark is weak, or no spark, before hunting down issues in the ignition circuit id do a voltage drop test on the battery. Could just be a weak battery. If no spark, and battery good, post and we'll help you troubleshoot.
4: if spark is good (jumps 1/2" gap) and the fuel in the tank is good, next I'd do a compression test on each cylinder.
5: if compression is good, spark is good and fuel in the tank is good, then we can conclude we've got a fuel issue. I like to keep a can of fresh fuel around and at this point I try dripping a little fuel directly into the carburetor and cranking to see if that allows the engine to start. If it still won't start with fuel getting to the carburetor, strong spark and good compression then I know it's time to rebuild the carburetor. On the other hand, if dumping fuel into the carb allows the engine to start up (and then stall out when it runs out of fuel) then I know the carb is fine and it's a fuel delivery problem. So I clean the fuel filter, try again. If no improvement I suspect fuel pump needs to be replaced.


I skipped over what to do if you have a no spark condition or what to do if compression is bad. Mainly cuz I suspect thats not your problem. But if you do have bad compression or no spark post the results and we can guide you through troubleshooting. By the way when you're doing these tests and posting results, it's much easier to help when your specific about the results. We like data here. Good luck and welcome aboard

This is awesome, thank you. I spent the afternoon getting the boats in cosmetically good shape and investigating engine bays, I’m going to get started on the homework here above and should have an update on whether the 3.0 engine cranks with a battery (that’s the one that was submerged in the yard- there’s a lot of corrosion apparent on what I believe is the starter and the alternator).

Also looking for Mercruiser manufacturer manuals .

 

[Scott Danforth]

throw the seloc manual away, or use it to prop a couch corner up. because as a manual it sucks. suggest getting factory manuals. https://publications.brunswick.com/

if you didnt use the larger boat in 2020, you need to completely drain and clean the fuel systems as fuel doesnt last that long. fuel probably turned.

the boat with the 3.0 that sat since 2016 may need to have the tank cleaned. what ever was in the tank is now varnish

is the 5.7 carb or EFI?

need year of manufacture or serial number of the two motors (cant quite read the pic) that way we know what ignition system is on them. the 3.0 appears to have the EST

most likely the stalling on the 3.0 was a mis-adjusted lower shift cable. performance may be wrong prop.

 

[Learning Still]

throw the seloc manual away, or use it to prop a couch corner up. because as a manual it sucks. suggest getting factory manuals. https://publications.brunswick.com/

if you didnt use the larger boat in 2020, you need to completely drain and clean the fuel systems as fuel doesnt last that long. fuel probably turned.

the boat with the 3.0 that sat since 2016 may need to have the tank cleaned. what ever was in the tank is now varnish

is the 5.7 carb or EFI?

need year of manufacture or serial number of the two motors (cant quite read the pic) that way we know what ignition system is on them. the 3.0 appears to have the EST

most likely the stalling on the 3.0 was a mis-adjusted lower shift cable. performance may be wrong prop.

The 3.0- they kept saying it had been fixed then we’d take it on the lake and it wouldn’t start or kept stalling again (this was the new engine). It would sputter on take off but if you could get it past that point it would run ok but then stall when you came to idle. Two different mechanics worked on it- first (the one who replaced the engine) replaced gaskets, switches, adjusted throttle and timing. Second mechanic said timing was way off and adjusted. Symptoms were always the same. First mechanic came on the water with me in 2018 to see first hand, did more work and declared fixed, it wasn’t, then in 2019 I found the second mechanic. When it didn’t improve with his tweaks I decided we would just always double pump to get through the 1000rpm danger zone and not go slow, which was problematic across every facet of boating.
Attaching pic of 5.7l engine specs. This one I think I have better chance at getting started.
-fresh batteries
-covered since last use
- fuel treated in 2019 but still has half a tank, looking for ways to remove fuel.
- looking at the basic or advanced manual from link above, happy to get the advanced one but wondering if it’ll be more like taking a college course without an instructor.

 

[76SeaRay]

Sounds like you need to focus on one engine at a time which sounds like the 5.7L. Work with it until you either get it running, determine it needs major work, or it is completely toast. Remember that you need 1) spark, 2) fuel, 3) air, and 4) compression for the engine to run. You can diagnose them in any order but most people start with spark and then to fuel as those are the most common issues on a fail to start. All of these have quick and dirty checks. 1) lay a spark plug on the block with the spark plug wire attached. Crank it over and see if you have spark. 2) open the throttle plates and while looking into the carb see if some fuel pumps when pumping the accelerator arm. Even before these you can try a little (very little) starting fluid into the carb to see if it fires over briefly. ALWAYS have a fire extinguisher at hand on any of the checks.

 

[Grub54891]

Don't know where you are at, but it sounds like you need to learn how to repair them yourself. The mechanics aren't so awful good from what I see.

 

[Learning Still]

So an update:

Still waiting for Mercruiser manual from Brunswick.
Found a NEW mechanic who offered to diagnose both for $99 each if I hadn’t fixed by check in date (today). I had not, so took both in.
Within an hour he said I needed a new battery and an oil change before he could test if it would start, $650. I declined and brought the bayliner 3.0l home, recharged the battery and changed the (water filled) oil.
I’m happy paying $99 for the “change the oil” advice (the battery was my bad as I forgot to put on charger).
So current status is:
5.7l full charge batteries and pending $99 diagnostic
3.0l pending battery replacement/oil change (bought the wrong filter so have to go back tomorrow)