Whipplecharged Mercruiser 502 mpi Operating Temp
 

I have a 1997 502 mpi with a sidemounted Whipplecharger (Whipple is a 2001 model). Boat has run fantastic for many years with this set-up, but I have a few questions that I'm looking for advice on...

Lately, I have noticed my temperature gauge creeping up toward 180 after some runs up and down the lake....even at just cruising speeds. I do not have a thermostat and was wondering if this sounds high? Even though outside temperatures have crept up into the 80s and 90s (and water temp is consequently warmer as well), I am paranoid that this is starting to run too hot. A couple thoughts.....could it be my impeller starting to go bad (standard Bravo I drive)? Or, do the impellers just kind of go bad all at once and it would be obvious it had failed (instant overheating)? Or, could it be that my intercooler is malfunctioning? As far as I know, the Whipplecharger (including the intercooler) has never really been serviced. Does coolant need to be added every few years? I'd also like to add....as weird as this sounds, I have noticed my engine exhaust sound suddenly get louder as I have been running down the lake (again, not full speed and only toward the end of the day after running at cruising speeds for a while). When I hear this louder exhaust sound, my gauges all read "normal" (other than the aforementioned temp gauge approaching 180). And, when I stop and let the boat idle for a second and take off again, the sound is back to normal. What in the world could cause the exhaust to suddenly get significantly louder....and, could it be related to my paranoia over the overheating?

When was impeller last changed? How many hours on it?

It has probably been 6-7 years since it was replaced (approx. 200 hrs?). I just wasn't sure if.....when an impeller dies, does it go all at once and it would show immediate overheating? Or, can it be a gradual failure over time where my operating temp might start creeping up higher than before (as I'm describing)? Like anyone, I don't want to replace if I don't have to.....but obviously if this sounds like a textbook example of a dying impeller, than I'll go ahead and do it.

Coolant ?? you're running closed cooled..........change the impeller and back flush the system

Used Impellers can get relaxed, can lose some of impeller, and impeller housing can get scored.

When you replace housing and impellar check for any blockages in sydtem, especially frt of oil cooler, fuel cooler, etc. Impeller, sea weed, pebbles, organisms, etc can block some tubes and thus water flow. If real old or used in salt water ar any times, rust chunks can get stuck beginning of exh riser passages.

Thanks. It is water cooled (not closed cooling like in the 496 or newer HP engines). It has never been run in salt water either. All of this is great info.....thanks. BUT....is anyone able to comment on the proper operating temp for a Mercuriser 502mpi w/a Whipplecharger (no thermostat) after several runs up the lake at medium throttle? I mean....maybe I'm just more observant than I used to be, and, it has always been creeping toward 180 on hot July days. Does anyone know what temp I should be running with that system?

with no thermostat it should not see 180 deg.as already stated change the impellor and check the coolers for trash.

Without a thermostat the temperature is dependent on the integrity of the cooling system. And at this point it appears the thermo-efficiency of your cooling system might be compromised at the impeller. With your setup I would be on top of the impeller changes every year. A hotter engine is more prone to detonation. Change out the impeller and housing new and see where you are at. It's a simple change.

It died about 4 yrs ago(LOL)! I think mercury states every 3 years max

Yes, under 140f. My ATI 502 MPI ran gawd awful low water temps eiyh their crossover and no t-stat. Usually under 120 and s lot needle sitting at 100f because of our lake being cool/cold 1/2 the time of boating season.