Mercury 525efi rebuild question
09-05-2024 | 01:01 PM
#11
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Not looking for any more horsepower, just need as much reliability as possible. This is primarily a fishing boat (29' Fountain Sportfish Cruiser) that I regularly take 50-100 miles offshore. Oil temps creep up and hold at 200 degrees if I'm in rough seas and have to stay off plane and run 1400rpm at 7-8mph. Temp drops to around 150 as soon as I plane out. I run two water pickups into a sea strainer. One on the drive and a 1.25" transom mounted unit. I also run the stainless double water pump. Water pressure never drops below 10 psi even at low idle. Oil temperature and headers used to get hot before I installed the dual pump and transom pickup. Oil would hit 220 degrees and headers would get really hot and turn gold. They stay cool now.
09-05-2024 | 02:15 PM
#12
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From: Washington State
Sending the oil out for testing is a great idea. Not sure why I didn't think about that. Especially since I send my truck's oil out once a year. Maybe I'll get lucky and only need to do a little work on the heads this year. The motor runs good but that oil pressure just really worried me. The slight loss of compression on two cylinders is something I have to fix now that I know about it... What 20/50 are you running? I will give it a shot and see if that gets the pressure back up a bit.
09-05-2024 | 02:20 PM
#13
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Sending the oil out for testing is a great idea. Not sure why I didn't think about that. Especially since I send my truck's oil out once a year. Maybe I'll get lucky and only need to do a little work on the heads this year. The motor runs good but that oil pressure just really worried me. The slight loss of compression on two cylinders is something I have to fix now that I know about it... What 20/50 are you running? I will give it a shot and see if that gets the pressure back up a bit.
09-05-2024 | 03:32 PM
#14
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From: St-Hyacinthe, quebec, canada
200 oil temp is fine, what oil have you been running and the weight? Nm i see you posted that. i like 20-50 in all the big blocks i build, your oil pressure loss is probably oil bearing clearance. Send in a oil sample to see. If nothing comes back then you just have a bad oil pump, Very rare for a bbc oil pump to fail.
At 230 there is clearly a thermosthat opening somewhere cause it drops pretty fast
what oil are you using? Not many x-50 available like it used to !
09-06-2024 | 12:49 PM
#17
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From: Waldorf, Md
Pretty sure that is what comes in those engines. At least every Mercruiser Big Block I have worked on had one.
09-07-2024 | 03:07 AM
#18
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From: BC
Running a 20/50is a great way to test out your low oil pres at idle. I would do it even to get info before teardown.
09-07-2024 | 07:32 AM
#20
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From: St-Hyacinthe, quebec, canada
For some reasons, each engines i tested on dyno were less powerfull on each pull using synthetic oil vs mineral, like losing 2-3 hp each time for 3-4 pull
i would then tear it down, hone it, reassemble, warm up and do couple pull, each time it was more powerfull and kept the same hp thru each pull...
go figure why, but it is what it is...
i would then tear it down, hone it, reassemble, warm up and do couple pull, each time it was more powerfull and kept the same hp thru each pull...
go figure why, but it is what it is...
