Compression Test Number 2004 5.7 350 MAG 260 Sundancer ... Real or Fake???
- Thread starter DjNiki4
- Start date
DjNiki4
Active Member
@Lazy Daze @scoflaw I looked over the survey that was send to me though the dealership i bough it it and this was their sea trial since i was not able to do sea trial when i bough it in February.
when i did 4690 rpms i was at 30 kts
when i did 4690 rpms i was at 30 kts
So they gave you a "diagnosis" and price without doing a leak down test? If so, run Forest run.
Moral of the story is always attend the survey and sea trial when selling. I would try to get the parties back to do a sea trial with you aboard. Then see what happens.
Moral of the story is always attend the survey and sea trial when selling. I would try to get the parties back to do a sea trial with you aboard. Then see what happens.
scoflaw
Well-Known Member
- Aug 10, 2011
- 6,395
- Boat Info
- 1999 Powerquest legend 260 sx 502 mag
2005 Baja 242 islander 496
- Engines
- 502 mpi Bravo 1
496 mag B1
LD should know how fast that boat should go. 32 sounds slow to me
LUnaCY
Active Member
If its your broker he needs to represent you better. If its their broker then they are trying to get a good deal. Let them be out the $ on the survey. Negotiate less. They want it and will pay. I hate games.
I agree - that is slow.
Is that speed via GPS? I suspect it is since the speedo is not (usually) labelled in knots. I was able to consistently touch 40mph (gps) on my 260DA (same hull), however I had the 260HP 5.7EFI as opposed to your 300HP 5.7MPI. My boat was never "light" with equipment, either. The 32kts sounds a little more inline although still slower than it should be. I did not have a tower or a genny - if you have those, that will account for some of the speed difference between yours and mine, but certainly not all of it.
DjNiki4
Active Member
@LUnaCY my broker which is why i am upset he didnt do shit to make the deal happened he let em walk.
@Lazy Daze - No generator but i do have a tower arch full tank of water amps subs gear etc. cooler and fridge both full ill have another mechanic look into it just to have a clear set of mind. and i might go on a ride tonight ill take more videos and data...
@Lazy Daze - No generator but i do have a tower arch full tank of water amps subs gear etc. cooler and fridge both full ill have another mechanic look into it just to have a clear set of mind. and i might go on a ride tonight ill take more videos and data...
BillK2632
Well-Known Member
I don't think there is anything wrong with your engine - yet. I would check the compression myself and if the risers have more than a few years on them I would consider replacing them. If the compression is a little low (even if it is still in spec) in the two middle cylinders it indicates water getting in through the exhaust. It doesn't take much, just a little after shutdown, then rust and corrosion go to work while you are not using the boat.
Not sure this helps you but here are my compression numbers for a 350MAG. The mechanic said they were perfect for what that is worth.
DjNiki4
Active Member
@BillK2632 thank you i dont think so either. i think the mechanic didn't do it properly. and/or has no idea wtf hes doing.
the manifods and risers were done end of season 2016.
the manifods and risers were done end of season 2016.
Here is the page out of the manual ....minimum 100psi and look at footnote 4
scoflaw
Well-Known Member
- Aug 10, 2011
- 6,395
- Boat Info
- 1999 Powerquest legend 260 sx 502 mag
2005 Baja 242 islander 496
- Engines
- 502 mpi Bravo 1
496 mag B1
Those are good numbers for a pre vortec engine. Vortec motors were about 25 pound higher.
The info you posted about the 100 psi is nothing more than a Mercruiser disclaimer.
Any engine guy knows a motor with that low compression will be a total turd, but it will run.
The info you posted about the 100 psi is nothing more than a Mercruiser disclaimer.
Any engine guy knows a motor with that low compression will be a total turd, but it will run.
When you take another run, definitely post back. Something is not jiving with your 4950RPM and 34/35MPH. Speed should be higher at that RPM.
Oh... take some of the extra stuff out of the boat. It's easier for us to judge/compare if you're just running with the normal equipment. Whether you do the compression test yourself or have someone do it, it should be pretty easy and quick - the bilge of that boat is a joy to work in.
Oh... take some of the extra stuff out of the boat. It's easier for us to judge/compare if you're just running with the normal equipment. Whether you do the compression test yourself or have someone do it, it should be pretty easy and quick - the bilge of that boat is a joy to work in.
Last edited:
boatman37
Well-Known Member
- Jun 6, 2015
- 4,256
- Boat Info
- 2006 Crownline 250CR. 5.7 Merc BIII
Previous: 1986 Sea Ray 250 Sundancer. 260 Merc Alpha 1 Gen 1
- Engines
- 5.7 Merc BIII
And if you do get similar results do a leakdown test. That will tell you where the leakage is and help point to the problem. But I agree with 100 being low. Also don't forget to factor in the calibration of different gauges. Sure you shouldn't be seeing a huge discrepancy but if your numbers are all 10 higher or lower don't panic, as long as they are all similar and withing about 10%
DjNiki4
Active Member
mnm99
Well-Known Member
He wasnt wrong about the numbers. 30psi is more than 10%.
