saltwater 5.0 weak points

[vroom ZOOM]

Hello, just picked up another project boat but this one has seen saltwater for 15 years (I think), and then sat for 5 more, it has twin 2005 5.0 MPI engines with dry joint exhaust. My concern is that these are open loop motors. What rots out on these engines first? I will be replacing the manifolds and elbows, but is there anything else to look for? Should I be pulling the heads? Intake manifold? One engine turns freely, the other I have not gotten to yet.

Although the anodes on the drives are rotted away, they must have done their job really well because the paint on the 20 year old drives is like new and shows very little corrosion, they are in surprisingly amazing condition for what I think is a wet slipped boat.

 

[Bondo]

What rots out on these engines first?

Ayuh,... A prime failure point is the intake manifold, under the t-stat housing,....

 

[Scott Danforth]

Even the dry joint manifolds fail in salt water taking out the motor.

Intake manifold and heads can rot thru
Having twins, my guess this was a moored boat?

If you got it cheap enough, throw two 350 short blocks in there and add heat exhangers

 

[vroom ZOOM]

Even the dry joint manifolds fail in salt water taking out the motor.

Intake manifold and heads can rot thru
Having twins, my guess this was a moored boat?

If you got it cheap enough, throw two 350 short blocks in there and add heat exhangers

Luckily, they didnt, and will be replaced before starting the engine up again
I would then need to reflash the ecm to update it to 350 spec. Sorry, this aint carb stuff. At that point I may as well build two 6.2s. Also I think the 305 heads wont fit a 350 short block? I do like the closed cooling idea though. I forgot to mention that the boat will now be used in freshwater only.

 

[Scott06]

Luckily, they didnt, and will be replaced before starting the engine up again
I would then need to reflash the ecm to update it to 350 spec. Sorry, this aint carb stuff. At that point I may as well build two 6.2s. Also I think the 305 heads wont fit a 350 short block? I do like the closed cooling idea though. I forgot to mention that the boat will now be used in freshwater only.

Yes need a reflash for either 5.7 or 6.2 displacement yes the 5.0 heads may have different chamber volume to keep compression at 9.4 don’t recall exact diffs but while folks have bolted them up to 5.7 s I think performance is Down

 

[Lou C]

I would evaluate what you have depending on budget. I’ve had the experience of running a raw water cooled cast iron GM marine engine for 15+ years in salt & what you’ll see is the exhaust is the first place to suffer corrosion. Beyond that the intakes can rust through under the stat housing, and the cooling passages of the heads can erode to the point where they won’t seal well against the head gaskets. So if the engines start & run OK and there’s no water in the oil, I’d do a compression test & see what you have. If any doubt you can pull the stat housings & check the intakes & if your comp test is low you can do a cyl leak down test. If no water in the oil your lower ends may be ok. To replace heads on 2 engines isn’t that bad of a job depending on access. I did mine without pulling the engine.

 

[tank1949]

That old of a boat and used in salt water, for peace of mind, I'd rebuild a 350 from a junk yard to a 6.2 and add close cooling (antifreeze). Pitch old salt water exposed iron.

 

[vroom ZOOM]

I would evaluate what you have depending on budget. I’ve had the experience of running a raw water cooled cast iron GM marine engine for 15+ years in salt & what you’ll see is the exhaust is the first place to suffer corrosion. Beyond that the intakes can rust through under the stat housing, and the cooling passages of the heads can erode to the point where they won’t seal well against the head gaskets. So if the engines start & run OK and there’s no water in the oil, I’d do a compression test & see what you have. If any doubt you can pull the stat housings & check the intakes & if your comp test is low you can do a cyl leak down test. If no water in the oil your lower ends may be ok. To replace heads on 2 engines isn’t that bad of a job depending on access. I did mine without pulling the engine.

Thank you for the info, I am not really limited money wise, more time wise. I think I will slap a new intake and exhaust on the existing motors and build some new ones over the winter.

 

[vroom ZOOM]

That old of a boat and used in salt water, for peace of mind, I'd rebuild a 350 from a junk yard to a 6.2 and add close cooling (antifreeze). Pitch old salt water exposed iron.

This is what I was really thinking hard about. Should I budget to bore the wrecking yard motor, or is a hone, line hone and re ring usually good? Do I need a forged or just plain cast stroker crank? I guess I will have to buy the mercruiser cam and lifters though so I don't run into trouble with the tune?

 

[vroom ZOOM]

Yes need a reflash for either 5.7 or 6.2 displacement yes the 5.0 heads may have different chamber volume to keep compression at 9.4 don’t recall exact diffs but while folks have bolted them up to 5.7 s I think performance is Down

I see new heads all over fb marketplace for peanuts, if I go to build a 5.7 or 6.2 I will grab a rust free wrecking yard motor to start off with, and for the $500 it will already have the correct heads.

 

[vroom ZOOM]

I apprecieate the insight from everyone, I think I will put a new intake and exhaust on my current 5.0 engines (Just checked yesterday and they turn freely, hooray!). Over the winter I might grab some wrecking yard blocks and build myself two 6.2 engines and sell the 5.0 ones to recoup some of the cost (or it all of it)

 

[Scott Danforth]

5.0 heads are 58cc with small valves

5.7 heads are 64cc with big valves.

The 5.0 motors are not worth that much as they are $300 from u-pull-it yards

Cost to rebuild a SBC has gotten stupid lately

 

[Pmt133]

Cost to rebuild a SBC has gotten stupid lately

My machinist told me their cost for a stock rebuild on a 350, nothing special, has almost tripled. I know for a fact I used to be able to get a full rotating assembly and gaskets for ~$600 for a stock .030 over 350 and maybe about the same for a 383 without searching for a deal... I took a quick peek and it looks like those same parts are in the $1200 range now....

I got a custom billet cam ground last year and the price was less than a cast off the shelf grind from someone like comp today for say the xm264hr...

 

[Scott06]

5.0 heads are 58cc with small valves

5.7 heads are 64cc with big valves.

The 5.0 motors are not worth that much as they are $300 from u-pull-it yards

Cost to rebuild a SBC has gotten stupid lately

I noticed when I did my repower a few years back right about the time GM discontinued the 5.0 that a lot of marine suppliers the 5.0 was more than a 5.7 . I guess if you needed a 5.0 instead of converting to a 5.7 and reflashjng ecm or tuning a carb they were going to tweak you cost wise

Now the new bases engines are about $2k maybe $2500 more than in end the of 2015

 

[Scott Danforth]

Today, if I was repowering a boat, I would most likely get low mileage LS or LT 6.2s from a u-pull-it, run a carb and install a heat exchanger and have 375-400hp for about $2500-3000 installed

To build an SBC 6.2 today to that level will cost $4k just for a long block

 

[nola mike]

Today, if I was repowering a boat, I would most likely get low mileage LS or LT 6.2s from a u-pull-it, run a carb and install a heat exchanger and have 375-400hp for about $2500-3000 installed

To build an SBC 6.2 today to that level will cost $4k just for a long block

I didn't think an LS or LT was straight forward? What about exhaust/intake?

 

[Pmt133]

I didn't think an LS or LT was straight forward? What about exhaust/intake?

Crusader and volvo have manifolds and elbows. All you have to do is fit them to the y pipe (some fabrication) or go through hull. Otherwise it's the same swap stuff as anything else. Mounts, wiring, etc.

 

[Scott Danforth]

Carb intakes for LS are on amazon for $140 they are chinese knock-offs of the holley and edelbrock that is only $350

Ls exhaust manifolds are less than SBC manifolds from BARR, etc. Crusader, Indmar, Ilmore and VP have all used the LS since it came out

for ignition, there is the front timing cover that has a dizzy (originally developed for racing to meet rules) or you can run a stand-alone ignition

 

[nola mike]

Ls exhaust manifolds are less than SBC manifolds from BARR, etc. Crusader, Indmar, Ilmore and VP have all used the LS since it came out

Nothing that will bolt to a Merc I/O I assume...I haven't ever seen anyone doing a conversion on here though.

 

[Scott Danforth]

Nothing that will bolt to a Merc I/O I assume...I haven't ever seen anyone doing a conversion on here though.

same flywheel housing pattern. GM didnt change that.