2005 Merc Opti. 776 hours. All 6 cylinders between 85 and 90 psi. Are those compression numbers low, or do you all think they're acceptable? Got that info from a dealer that has a Ranger I'm looking at. Thank you, guys!
2005 Merc Opti. 776 hours. All 6 cylinders between 85 and 90 psi. Are those compression numbers low, or do you all think they're acceptable? Got that info from a dealer that has a Ranger I'm looking at. Thank you, guys!
Not sure if they're low for that motor, but good that they are all within 10%. My guess, they may not have had the engine to running temp. That can give low number. I know my OMC Fucht tested to around 90psi and that was considered good cuzz they were all 90. They should also do a leakdown test for you.
2017 Phoenix 819
2016 200ProXS, s/n 2B359849, Mod 1200P73BD
Depends on the accuracy of the gauge and if the test was completed on a warm motor, with the throttle plate wide open.
Click on this >>>>>Performing Compression Tests
Ugh, yea, I've been reading a lot more since posting this. Seems like a lot of variables. I can't help but think that compression in the 80's for pretty much any reason is not a good thing.
I wouldn't give up the ghost just yet. Ask the dealer what the deal is and ask for a leakdown test too. Maybe the dealer isn't doing their part to do it correctly. On the other hand, there are A LOT of good deals to be found so don't get hung up.
2017 Phoenix 819
2016 200ProXS, s/n 2B359849, Mod 1200P73BD
Compression tests are really just for diagnostics, like looking for a dead or very weak cylinder.
If you want to know the performance potential of a powerhead, a leak down test is needed.
"Better to remain silent and be thought a fool than to speak out and remove all doubt."
OK, they're doing a leakdown test for me. Is there a % or range or something that I should be looking for?
Most of the earlier 200 & 225 Optimax (non XS0) motors came from the factory with around 90psi because of the compression relief notches on the top of the exhaust port. I do agree that a leak down test will tell you more about the condition of the cylinders. Anything over 7 or 8% and I would be looking for something wrong.
Thanks much, guys. Awaiting that leakdown test result now.
I went through this process about 9 months ago with a 2004 optimax. The motor only had 256 hours on it. the biggest thing that I learned is that the compression should be within 15% across the board. My readings were In the 125 range with the low being120 and the high being 130. A second gage once I got it home read 10lb less across the board. both brand new gages. get the leak don test and make sure across the cylinders you stay within the 15 %
If you would, please take a moment to review the Forum Announcements, and be sure to provide the Required Info when posting. Thanks!
Compression, when done CORRECTLY (see Post# 3) should be consistent. 90-110 range, max variance of 15 psi between lowest and highest cylinders.
Depending on the serial number, it's possible you might see slightly elevated numbers on 3 and 4 (not uncommon with some models).
Leakdown is an excellent measure of bore health. If you don't own this engine, don't even consider it with more than 6% leakdown. Most any reasonably healthy engine of this series will be at 4% or lower.
Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor
Thanks guys. Very informative info and I learned a lot.
Any updates?
2001 Ranger 518DVX Comanche / Mercury 200 Opti (OT306368)
Someone bought the boat while I was going back and forth with the sales guy. Never heard any response from the leakdown test.
Forum rules state that you have to start a new thread.Originally Posted by Richie B
Reply With Quote
