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Jumpy Oi Needle

Old 04-24-2002, 07:32 PM
  #1  
pmcrespo
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I had my 27' w/stock carb 502 out last weekend and I realized that every time the rpms went passed a certain point, at about 3,500, my oil pressure gauge needle started to bounce erratically betwwen like 50 and 25. But then, as soon as I throtled down, the needle would become stable at about 40-45. It continued doing it every time above that mark. It almost appeared like pressure would dissapear and then reappear before it ever hit 0.

Before I start replacing half the boat until I solve the problem; Do any of you have any idea of what could this be? Obviously, first part in mind is the sender.... But someone mentioned once something about some oil pressure controller actuator with some spring that could make this happen...??? Any ideas?
 
Old 04-24-2002, 08:23 PM
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You have just described the classic symptoms of too much oil in an engine. With an overfilled crankcase at high rpm the crank whips the oil into a foam. Foamy oil will not hold pressure because the air in it is compressable.

Too little oil will cause a similar condition.

I would check the oil level. The manuals say to check it while the boat is in the water.

If the level is ok check for a loose ground or signal wire on the gauge and sender. If all the connections look good replace the sender.

Hope this helps

Ron
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Old 04-24-2002, 08:38 PM
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pmcrespo,

Mine did the jumping thing. It ended up being a bad sender. You can pull it and see if it is plugged but for peace of mind I'd just replace it. If you have Gaffrig gauges I'd recommend going with the Gaffrig sender. My oil pressure now reads 20 lbs. more. The merc sender that Fountain uses doesn’t match the gauges.


Dan
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Old 04-25-2002, 10:20 AM
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mine did the same thing (96 27 w 502MPI) and it turned out to be a loose wire on the sending unit.
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Old 04-25-2002, 11:49 AM
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Thanks guys. I will have to check both the level and the sender. I'll also check the wire at both ends indy.

Ron, you just answered another question. I had been checking the oil while on the trailer. I presume it gives a different reading since the boat is much more leveled.

Dan, thanx, I will just go ahead and replace the sender too as I am in the process of ordering new Gaffrig gauges.
 
Old 04-25-2002, 12:22 PM
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Default While on the oil subject...

Sorry about the seemingly ignorant questions, but I just got the boat and I am trying to learn as much I can from you experts on Fountains.....

I am using Marine Racing 50 weight oil. Any recommendations on this? How about additives such as Prolong and the such?

The previous owner also recommended to use that "Liquid Horsepower"/Octane Boost for the fuel. Do they "really" make a difference? I am not really running any advanced timing or anything along those lines, stock carb engine with just a K&N filter and HP Ignition coil....
 
Old 04-26-2002, 12:25 AM
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I had a 92' carbed 502 in a Checkmate. I used 89 octane. It didn't run as good on the 92 octane. I know the 502's with knock sensors had to run on 87 octane or the computer wold retard the timing because it didn't since any knocking. I ran my timing at 12 degrees initial advance with a total of 36 at wot. It was a lot crisper at idle. I used 15W40 Mobil One in that engine. I now use straight 40 and change it often. Usually 20 hours or less. I use to run Delco filters but have switched to Wix filters available at Nappa.

I would repost this in the tech section. I'm sure you will get many more responses.

Dan
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Old 04-26-2002, 08:21 AM
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The manual on my 500hp carb says to run 87 octane. I usually run 89, but never 92+. It doesn't run as good. I don't ever use any additives in the boat or cars. Some people swear by them and some swear they do nothing but damage. if you're running a stock 502 I recommend 89 octane. Especially if you buy your gas on the water.
 
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