Engine overheats at idle, cools at 15k RPM's.

R

Rocky Coast

.
Nov 27, 2021
8
Catalina C30 Portland
1984 Catalina 30, Westerbeke 25XP diesel. New boat to me, on the hard running on hose to salt water intake, no load. When boat idles it runs hot, up to 190-200, I won't see how hot it will get. Push up to 15k RPM's and temp drops to normal. Had water heater that is still plumbed with engine coolant, leak in tank on sink water side so bypassed. There is a valve diverting coolant to hot water tank, when valve is closed, pushing water through water heater, it overheats at idle and runs 160ish at 15K rpm's. When water heater diverter valve is open, allowing direct flow through heat exchanger, it runs 160ish at idle and 140ish at higher rpm's.

Heat exchanger just serviced and tested, 160 degree thermostat, functioned properly in pot of water with meat thermometer. Engine starts easily with pre heat and runs smooth (no load) minimal smoke at start up. Engine running temp spec is 165-195. Fairly new fresh water pump. Makes good water of of stern (there is some pressure from hose). Have not tested gauge but is very consistent with symptoms.

Any insight? Experience with similar situations?
 
D

dlochner

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Jan 11, 2014
12,955
Sabre 362 113 Fair Haven, NY
How is the impeller? At low rpms it may not be pushing enough water, at higher rpms it does.

Be careful using a hose to feed the cooling water. Safer to use a bucket. Put a hose in the bucket to the pump and fill the bucket with a garden hose as needed.
 
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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
23,139
CAL 35 Cruiser #21 moored EVERETT WA
Rocky Coast said:
15k RPM's
Click to expand
WOW... At the speed you could lift off...
I think that has to be... 1500 or 1.5K...

@dlochner has a great point. The pump is designed to draw water in not to have it force fed. A direct hose connection could add air to the water cooling and create cavitation in the system. Better to draw the water in from a bucket.

Until the temps get up to a certain point the thermostat is shut. A low RPM i.e. 6-800, the thermostat would be shut allowing the engine to heat up.

That may be a factor in seeing the high temp till you increased the rpm and increased the raw water flow through the system.
 
Don S/V ILLusion

Don S/V ILLusion

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Sep 25, 2008
7,435
Alden 50 Sarasota, Florida
jssailem said:
WOW... At the speed you could lift off...
I think that has to be... 1500 or 1.5K...

@dlochner has a great point. The pump is designed to draw water in not to have it force fed. A direct hose connection could add air to the water cooling and create cavitation in the system. Better to draw the water in from a bucket.

Until the temps get up to a certain point the thermostat is shut. A low RPM i.e. 6-800, the thermostat would be shut allowing the engine to heat up.

That may be a factor in seeing the high temp till you increased the rpm and increased the raw water flow through the system.
Click to expand
Good point plus we don’t know if it’s just a figment of an old thermostat reluctant to open.
 
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R

Rocky Coast

.
Nov 27, 2021
8
Catalina C30 Portland
Thanks for the replies, 1.5k RPM's, excuse the typos please. Thermostat works well in pot of hot water with meat thermometer but is a potential culprit. Also with hot water loop open it runs at temp at idle and cool, 140ish, at high rpm"s? Hose is from shallow well and barely open valve, sea strainer not full, but fair point on pressure water. Has worked fine on other boats. will try bucket feed. Thought system might be air bound due to having it apart to refurb heat exchanger etc.. Have not checked raw water impeller yet. jssailem, stat is on fresh water side and runs close to 200 at idle before I increase rpm's and that sends temp down, it is curious.
 
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Stu Jackson

Stu Jackson

.
Feb 26, 2004
23,047
Catalina 34 224 Maple Bay, BC, Canada
1. Make sure about your plumbing to the water heater. If it is shut off, it could also shut off the freshwater coolant flow. Depends on how it's plumbed.

2. Engine Overheating 101 - How to Burp Your Engine (Reply #6) Engine overheating problem (with Instructions "How To Burp!")

3.
Winterizing an Engine on the Hard (Thanks to Maine Sail) - NEVER connect a hose to your raw water pump inlet - NEVER!!!


Also:

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too :) This includes a link to the Critical Upgrades topic which has more engine information please read it too.

Diesel Engine - c34.org
 
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R

Rocky Coast

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Nov 27, 2021
8
Catalina C30 Portland
Hi Stu

1) Water heater is plumbed with a bypass, either through water heater or with open valve close loop to heat exchanger and water will take path of least resistance.

2) I do not really think it is air bound since it functions properly, (heats and cools) just erratically.

3) Thanks for the informative video. I am struggling to understand how an engine could get hydro locked with a hose attached to raw water side when the the raw water and fresh water are isolated from each other, perhaps if the heat exchanger failed and pressure water was pushed through heat exchanger into engine. I have been winterizing that way for years without issue.

My current theory is raw water impellar is tired and that is why RPM's affect performance. Going back in tomorrow AM.

Thanks for the feed back and will explore Engines 101.
 
D

dlochner

.
Jan 11, 2014
12,955
Sabre 362 113 Fair Haven, NY
Rocky Coast said:
3) Thanks for the informative video. I am struggling to understand how an engine could get hydro locked with a hose attached to raw water side when the the raw water and fresh water are isolated from each other, perhaps if the heat exchanger failed and pressure water was pushed through heat exchanger into engine. I have been winterizing that way for years without issue.
Click to expand
The water goes through the heat exchanger and is then injected into the exhaust. It fills the exhaust and backs up through the exhaust manifold. Same thing can happen if the sea water intake is open and the engine won't start the water pump will fill the exhaust system but not have enough power to push it out the exhaust, it fills and backs in through the exhaust manifold.
 
R

Rocky Coast

.
Nov 27, 2021
8
Catalina C30 Portland
So if the exhaust is still pushing water is it still a problem? I always make sure it is making water.
 
D

dlochner

.
Jan 11, 2014
12,955
Sabre 362 113 Fair Haven, NY
Rocky Coast said:
So if the exhaust is still pushing water is it still a problem? I always make sure it is making water.
Click to expand
Depends, if the exhaust is powerful enough to keep pushing the full flow. Worse than hydrolocking while trying to start is hydrolocking while the engine is running. All the moving parts suddenly stop.

You could use the hose a dozen times and be fine, but what about the 13th? The damage that can be wrought is just not worth the slight inconvenience of using a bucket as an intermediary step. You may of course have a different opinion of the risk.
 
R

Rocky Coast

.
Nov 27, 2021
8
Catalina C30 Portland
Thanks for the reply

I can see how it could be a probem if some part of the system is not functioning properly. I will draw from bucket going forward.
 
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