Over Heating

[Wind Chime]

I need some advice,

We have a 2000 with the Suzuki DF50 that has over heated 3 times this year.

The temp light comes on, over heat beeper alarms sounds, can not get over 3000 rpm's or it stalls. If I wait at idle for about five minutes, it is fine.

This only happens when we run at WOT to empty ballast. Usually only around 10 minutes or so, sometimes a little longer when I need to get the navigator home cause she's had enough.

I took it to the machanic, and he says he can't get it to repeat...of course.

The specs say the engine should run 5900-6500 rpm's at wot. We run wot at 6600 rpm's, making 16 knots.

Should I change the pitch of the prop to solve this problem?

I understand that for every "one inch in pitch +/- = 200 rpm +/- ". So if I increase prop pitch up one inch, that would get my rpm's down 200 to about 6400. Would that be enough to correct this problem?

p.s. impeller and cooling intake and p-hole is ok.

Help ...

[kmclemore]

When is the last time the water pump was serviced, and are you in salt or fresh water?

[Wind Chime]

The motor is 8 years old and we've had it 3. There is no previous owners service record for it and never had any work done on the pump, but was just in the shop for tune-up and spring check and given the OK.

Always in salt water, and flushed after every use.

thanks for any help

[Boblee]

Our etec has only given the temp alarm once and I believe there was a bit of weed over the hole when running wot but stopped and idled and it has been ok since.

[noahvale]

I usually replace my water pump every couple of years. Also I never run OB engines anywhere near max rpm. A larger prop will decrease your rpm and possibly give you more power, but there is no way to tell without changing the prop.

[kmclemore]

Water pumps don't last as long in salt water than they do in fresh. Most manufacturers recommend changing them out annually, but I think that's overkill. That being said, the first thing I'd do is to drop the lower end and replace that pump, particularly as you don't know how long it's been in there. Like as not, it's the original one!

[TAW02]

Wind.

Get the motor manual for that thing. That would be the first thing on the shopping list. Be suprised how that blows the fog away.

It's been my experience with motors that the rated specs are normally Minimum/Maximum. So if Max is 65K that means total warrantied Maximum. That also means if you run an extended period of time at the Max rate, you can expect all kinds of things to happen. Shortened life in the powerhead doesn't even rate compared to life down there in the lower-end (gear case). Doing 1K rpm over that, expells your warranty. Not familiar with Suzis, but many like Etec can record histories. Dealers can tell immediately what you've been up to when they dump flash memories on these units.

Be careful. Be easy on the max rpm.

Big T

[Moe]

You're probably WAY overdo for a water pump impeller replacement. I'd replace it every 3 years in fresh and 2 years in salt water. Overheating is a good way to ruin a motor.

If you are going to do your own maintenance, the service manual is priceless. For example, you wouldn't know to disconnect the shift linkage up high just under the bracket without it.

The service manual and water pump rebuild kit can be ordered from Brown's Point Marine Service.

[Wind Chime]

Good advice guys, ... thanks!

I am going to:
1. buy a new prop with 1 more inch of pitch, so that when I need to be at WOT, I will still be under the max rpm of 6500.
2. replace the impeller at the least, if not the whole water pump.
3. buy the full-on service manual (and actually read it). I have the short mini-manual (if I can find it), and I think I looked at the cover once.

The navigator hates it when reality things like engine trouble creep into our paradise. We have an ongoing list of; I hate sailing, let's sell the boat , and, I love sailing let's keep the boat (for another year).

Thanks again guys ... very much appreciated.

[Moe]

1. buy a new prop with 1 more inch of pitch, so that when I need to be at WOT, I will still be under the max rpm of 6500.

If you're getting 6,600 rpm when unballasted, I wouldn't. 100 rpm isn't worth worrying about. The DF50 has a rev limiter that won't let the rpm go above 6,800 rpm (you'll find that in the Service Manual when you get it). The DF50 is a small, displacement (for this boat), high-revving 4-valve per cylinder OHC motor that doesn't have a lot of torque. It can use the reduced pitch when ballasted, plus at least theoretically, the boat speed at idle is a little slower, so maneuvering around the docks.

[bo stout]

hi, new to the site. i too have had similar overheat problems on my '97x w/nissan 50. i pulled it, replaced impeller and put on stiffer prop, still overheats at near full throttle. when the buzzer sounded again i put in nuetral and felt water temp exiting motor and it is just luke warm. i spoke to the owner of marine repair shop about possible overheat buzzer malfunction and he said probably not, he had a theory about possible air bubbles from hull turbulence causing water pump cavitation this makes the most sense to me so far. when i trim the boat up at WOT it happens more quickly than when trimmed all the way down. i have yet to check if i can lower the motor on the transom. any thoughts?

[James V]

Mecury recomends checking the theromostat every oil change. You may have blockage.

I would not worry about max RPM's of only 100 over. Just find a few hundred pounds of stuff to put in the boat and it will lower.

You can also check the plugs and get some cooler running spark plugs.

[Ivan Awfulitch]

I had something similar happen with my Honda. Seems that I had set the trim out a bit too much and the prop was cavitating. I trimmed down a bit and haven't had the problem since. Only happened at or new full speed and wide open throttle. And there was a stream out of the pee hole when this happened.