you do need the stats as the engines will not come out of closed loop , the preset engine parameters a fuel injected computerized engine runs on until it reaches operating temps.
i believe the engines have fuel coolers and powers steering coolers. alot of times debri, old impelleer material, mostly eel grass and other shreded water bourne debri get caught in these areas and cant be back flushed without seperating the joints between each cooler, when you try tobackflush without doing this the debri dislodges from say the p/s cooler but ends up lodges in the outlet side of the oil cooler being it is up stream from it nad yuor back flush. the n you start the engine and force the debri back intop the p/s cooler. by flushing each component of the cooling system seperately you truly remove all debri.

its worth a shot as this is a very common issue i come across probably 15 to 20 times a season.

Thanks for the info,
I will email it to my brother and maybe over the weekend we can get down there and take the sytem apart.
I was suggesting swaping the oil coolers from one engine to the other and see if the problem moves with the cooler.

I will tell him to put the thermostat back in for sure. I should have known it would cause that issue we see it race cars all the time.

I guess I just expect the car thing to be different.

Thanks again guys.

hi oil temp
 

change to a large wix or fram oil filter had the same problem, this did the trick.

Isn't there an oil thermostat on merc motors. I seem to remember replacing one once. In fact I know for a fact there is on the hp 500.

Mercury OIL THERMOSTAT
OIL THERMOSTAT

Merc Part Number Variations
812307
8 12307
81 2307
812 307
81 23 07

Do you have a kinked line or a line to a cooler that is collapsing inside? Also have you verified flow thru your oil cooler??? Also how long have you had this set up? Have you done any perf upgrades? Is it possible that your cooler is too small? Just food for thought.. ;) Jamie / Lakeside

What are your water temps and oil pressure doing? Are you burning oil?

oil temp
 

my 94 fever w/502 mpi mag runs 245 all day long.if i run hard,rpms around 4000 i might see 250.i had the engine apart last winter and no signs of heat issues.i was told also that 245 was not a problem.i wonder though if that kind of temps is probley why my oil turns dark after about 15-20 hrs.i dont know.i wil say the motor had 445hrs on it before i r/r and was running great.

Any luck on resolving your oil temp issue yet?

I have had three fountains and all of them have had oil temps run right around 200F with oil warmed and running at cruise speed. Always interested when someone highlights an out of normal instance.

Eneryone else has basically torn apart the oil plumbing system in the previous posts . Not to revisit any discussion thus far, but what kind of oil is being run in the engines? There was an article by Bob Teague in Powerboat maybe six months back where this same condition was occurring, and the issue turned out to be that owner was running 10W30 motor oil in the engine. The oil couldn't handle the amount heat being rejected and immediately bypassed the filter, and was causing all sorts of weird indications.

I figure your probably running at least 40W in your engines or 20W50 so I would be surprised if this was the issue.

I switched to the AMSOIL AHR 60W last year and my 525s really like that oil. Hardly any soot on the transom and the oil is staying much cleaner. And the oil pressure increased about 10PSI over the entire operating range.

Just a thought.

Is there really an oil thermostat on 502 mpi's?