Engine Hot at Low Speeds

[mdiggs]

My 67/68 Donzi 16 with Ford 351 has a funky quirk lately. The engine seems to get hot when I run it a lower speeds/rpms. Any time I'm in a no-wake zone putzin' along for several hundred yards, the engine temp starts to rise.

Any suggestions on why? How to fix it? I'm incline just to go faster, but there's gotta be a better answer. Is it possible that the water cooling intake on the outdrive is not getting enough water when the boat is going slow, not planing, creating a bigger wake with a bigger well?

[MOP]

First thing is to establish just how much water is flowing from your pump at low speed, this is done on a cold engine at idle. Remove the outlet hose from the raw water pump and put it in a bucket, start the engine at idle it should put about 3/4 of a gallon in the bucket. 1/2 is just acceptable or should I say bordering marginal. If you have through hull exhaust you can get a good idea of how much water is getting out, there could be some blockage in the manifolds risers.


Phil

[Tony]

I had the same problem one year at AOTH. Turns out I had a hairline crack in the plastic inlet fitting just inside the transom. While on plane at speed I was fine, but at idle or off plane it was sucking enough air to not cool the engine.

Also, on my last boat, the 38 year old raw water pump housing had worn down enough to not pump strong, even with a new impellor.

Good luck!

[jl1962]

Interesting thread.

I'm just back from a few weeks at Lake George. The boat ran great but for the first time, the thermostat would spike 40 or 50 degrees when coming off plane. After 30 seconds or so (it always seems longer), the thermostat would drop off to normal almost as fast. The boat normally runs very cool (under 150) but would spike to over 180 when coming off plane. The boat is OK at idle and OK at speed.

Tony - was your AOTH issue w/ the Ski Sporter?

Jay

BTW - Welcome to the Board Mdiggs - that's a special boat! And only 10 hulls away from mine. Take good care of it and get up to LG sometime.

[MOP]

To test for air intrusion into the cooling tract, take a clear hose and put it between the Tstat housing and the inlet to the manifold.

Volvos usually suck air at the swivel Oring as the boat goes on plane when the mid section of the drive rises out of the water. The inner fitting being cracked is a rare one, Tony's is the only one I have heard of.

[Tony]

Jay, it was my 22' that had the hairline crack at AOTH.
Your Ski Sporter has a relatively new (5,6 years?) raw water pump housing, so your current problem shouldn't be related to that.

:beer:

[maddad]

I was getting air in my cooling loop from my Volvo outdrive. Switched to a through hull water pickup and all my overheat issues vanished.

[mdiggs]

Interesting thread.

I'm just back from a few weeks at Lake George. The boat ran great but for the first time, the thermostat would spike 40 or 50 degrees when coming off plane. After 30 seconds or so (it always seems longer), the thermostat would drop off to normal almost as fast. The boat normally runs very cool (under 150) but would spike to over 180 when coming off plane. The boat is OK at idle and OK at speed.

Tony - was your AOTH issue w/ the Ski Sporter?

Jay

BTW - Welcome to the Board Mdiggs - that's a special boat! And only 10 hulls away from mine. Take good care of it and get up to LG sometime.


Thanks. It's the family boat. Dad bought it new when I was about 4, gave it to me last year because, at 79 y/o, he decided he was ready for a pontoon boat. After driving it across the country from Maryland to Oregon last year, I'm not sure we'll be taking it anywhere but to the Columbia River ;-) That continental divide was something else!!

[mdiggs]

First thing is to establish just how much water is flowing from your pump at low speed, this is done on a cold engine at idle. Remove the outlet hose from the raw water pump and put it in a bucket, start the engine at idle it should put about 3/4 of a gallon in the bucket. 1/2 is just acceptable or should I say bordering marginal. If you have through hull exhaust you can get a good idea of how much water is getting out, there could be some blockage in the manifolds risers.


Phil

I'm a mechanical dunce, but I figure I can look at the exhaust. The manifold is new (see my post from June) but it had the same problem before we swapped out the old manifold for the new cast iron ones. I'll get a real mechanic on it right away.

[jl1962]

Thanks. It's the family boat. Dad bought it new when I was about 4, gave it to me last year because, at 79 y/o, he decided he was ready for a pontoon boat. After driving it across the country from Maryland to Oregon last year, I'm not sure we'll be taking it anywhere but to the Columbia River ;-) That continental divide was something else!!

Ahh....my bad - I thought it was another certain red '67 Ski Sporter! Take good care anyway!!!

:wink:

[mdiggs]

Ahh....my bad - I thought it was another certain red '67 Ski Sporter! Take good care anyway!!!

:wink:

No bad on anyone's part. Most people with Donzis "have Donzi....will travel" to other places for events. We're having fun on the Columbia...nothing like flying a 16 across the wake of a huge Navy vessel or tug pushing old growth trees down the river.

[mdiggs]

Interesting thread.

I'm just back from a few weeks at Lake George. The boat ran great but for the first time, the thermostat would spike 40 or 50 degrees when coming off plane. After 30 seconds or so (it always seems longer), the thermostat would drop off to normal almost as fast. The boat normally runs very cool (under 150) but would spike to over 180 when coming off plane. The boat is OK at idle and OK at speed.

Tony - was your AOTH issue w/ the Ski Sporter?

Jay

BTW - Welcome to the Board Mdiggs - that's a special boat! And only 10 hulls away from mine. Take good care of it and get up to LG sometime.


BTW, Hull number is 16369. Gotta love it.

[thescooter]

try repalcing the raw water impeller. also ,check to see if you have any leaks of air suction. the easy way is to put a clear hose like a fresh water supply hose on all your intake water lines before your pump. if you see air bubbles you have a air leak with the motor is running. on the vovlo their is a black rubber gasket on nthe drive that sometimes needs replacing. you can all so pumpwater out of a 5 gallon bucket to check the above problem to more locate your exact location of troble shooting the problem. go luck thescooter scooternicky@yahoo.com