fastech

I have a pair of 502 mag mpi's raw water cooled in a 1999 Formula 353 Fastech. My starboard side engine overheats when the boat is run above 4800 rpms. The engine cools off when dropping off plane. The outboard exhaust riser is warmer than the inboard side at all rpm. Replaced my raw water pump with no change. Boat is run in fresh water only. Any information would be appreciated. Thank you

johnny b good

I am not an expert on this, but I would back flush your cooling system,hoses,oil cooler, etc. oil cooler could have some blockage such as pieces of old impeller, seaweed,pebbles etc. take winterizing drains out and make sure you don't have sand built up in the engine. Might not hurt to check/replace thermostat in case its not fully opening. You can probably find a ton of info on this by doing a search on this forum. Good luck.

madbouyz

' search function ' ... oh yeah , you'll see a ton of stuff on this come up !

The first thing you really need to do is make sure you're getting good 'feed' to that engine at the water (raw) pump.
Don't waste any more time changing parts . Compare it's flow to the engine that's OK and then go from there.
And don't forget the very last thing it seems that comes up on overheating threads ... the transfer tube through the trans plate . It corrodes down and closes up the flow . will puzzle the heck out of you ... my friend just went through this with a pair of 350 mags.

obnoxus

Id start with backflushing.

If you can get to the cooler even better,,, I just did a boat we backflushed and still ran warm.

Pulled the cap off the rear cooler and found 12 pieces of impeller jammed in there

fastech

Thanks for the tips everyone. We purchased the boat in July of last year, it ran great almost the entire season. To shed a little more light on the problem, we were following 2 other boats out of a shallow area. we must have picked something up on the way out because the starboard engine overheated a short way down the lake. When we arrived at the marina I pulled the water lines from the circulator pump, oil cooler and risers. There was quite a bit of sand and debris. I also pulled the plugs from the block and manifold drains. All were full of sand.I have also changed the raw water pump on that engine. The old pump impellar was intact.

266ltd

on the 2000 502' mag, which is what i have, usually the first cooler will dam up all the imperller parts and keep them from going farther. The holes for the water through it, are really small and honeycomb looking. i belive it is the power stearing cooler, which is on the back of the motor. i would disconect the raw water hose after the pump and check there. I have had the same prob. a coulple of times and low and behold there the rest of the impelers were. I back flushes with slightly high presure and they would not, and i mean would not come out, had to use needle nose vice grips to pull each one out, and there were several, and it was tuff to pull them out even with grips, lucky i didnt have more of a heat problem. also fine round pebles can clog some holes in the coolers, coat hanger is about the same diameter for poking them out.
good luck

obnoxus

Ah,,,, OK,,, pul the block plugs and run the motor,,,,, see what comes out.

The block is packed with sand.

Griff

You've still got sand in the engine. the sand packs itself in and is a biotch to get out.