Engine overheating

dhagen · June 27, 2022, 05:36:00 PM

Today, when motoring out of the marina, the engine was working fine until I ran it over 2,000 rpm. At that point, the engine overheating alarm sounded and the temp was almost 240. I shut the engine down and checked the raw water strainer, which had a few pieces of seaweed, but not much. I cleaned it out. After sailing, I headed into the marina at idle speed, water was coming out the exhaust, and I had no overheating. In the slip, I ran the engine at idle and checked the exhaust and all was well. Temp was 160. I moved up to 1500 rpm and all was well. Same at 1800. But once I got over 2,000 rpm, it started to head to 200. I am assuming I have a cooling inlet hose that is collapsing at 2000 rpm. Does that sound reasonable? I haven't taken the water pump apart to check the impeller, but will. I don't know that the hoses have ever been replaced. La Buena Vida is a 2001 C34 mkll, with the M-35 B engine. To replace the hoses, does anyone know how long each is and the diameter of each? I printed the diagrams on the WIKI, but the I don't know if the diameter of the B hoses is the same as the older ones on the WIKI. Any help or advice would be appreciated.
Dan

mark_53 · June 27, 2022, 06:49:13 PM

Did you check if the thru hull was clogged? Take the strainer off and shove a dowel through the thru hull to clear any obstruction.

AndyBC · June 27, 2022, 08:53:50 PM

Yes good idea to check the condition of the impeller. Also, did you check the coolant level? When was the last time it was changed?

Is the freshwater/coolant pump functioning properly?

Have you checked the heat exchanger?

dhagen · June 28, 2022, 11:44:07 AM

The way mine is plumbed, I can't just push a dowel through the strainer. I am getting water out the exhaust, so I don't think that is the problem. The impeller is fine. The coolant was changed a couple of years ago and it shows full. I'm not sure where the coolant pump is. I am thinking it may be the thermostat. I know that hasn't been changed since new.

Ron Hill · June 28, 2022, 12:01:47 PM

Dan : FYI all of the suction hoses should be wire reinforced so they should NOT collapse. The other hoses on the pressure side of the raw water pump might be wire reinforced?, but they don't have to be!! I'd check all hoses and make sure there is no kink in the hoses that might cause a reduction in the flow of raw water.

A prime suspect is your impeller - check it and make sure that all blades are intact. As mentioned also make sure that the RW thru hull is fully open and clear of seaweed!!

A few thoughts

Stu Jackson · June 28, 2022, 06:05:40 PM

I have successfully cleared a blocked thru hull by removing the hose from it to the raw water pump and blowing back through it with a dinghy foot pump.

Also, check that your raw water pump faceplate is flat, flat, flat and not scored.

It sounds like you are on the right path of the usual suspects.

KWKloeber · June 28, 2022, 09:54:12 PM

Dan you cannot ass/u/me anything.

Without you saying how new (or old) the hoses are it's hard to guess what is the cause.

If the hose is the problem, squeezing it will tell you if it could collapse under suction. A wire-wound hose in good condition you cannot squeeze closed with your hands. The only hoses that are under suction would be the one from the Hx back to the coolant circulation pump and the supply hose to the seawater pump.

I'd think it likely might be a blockage in the system (weeds or a piece of impeller stuck in the Hx -- pull the inlet side end cap and check for junk.) Partial blockage of the Hx would have a similar result as the old M-25 owners who had the original 2" Hx. No overheat at low RPM but overheating when pushing the engine. Or an issue with the Seaward brand pump/impeller.

scgunner · June 29, 2022, 10:42:22 AM

Dan,

Your system is designed to draw more water as the RPMs increase. If there is a partial restriction, the first thing I'd suspect, it won't draw enough water to cool the motor at higher RPM. It's also possible it could cause a hose collapse. An easy check can be done at the slip. At idle the exhaust water will "spit" out intermittently the spitting will increase in frequency as the RPMs increase and should continue to increase until max RPMs are reached.

If the volume of exhaust water stops increasing somewhere before max RPM is reached there's probably a restriction. Another indicator would be the exhaust water itself, it should never be more than warm to the touch.

karista · June 30, 2022, 08:44:39 AM

Had the same problem about one year ago, ran fine and cool at lower RPM's but quickly went up over 2200RPM. Did this consistently. Checked all the obvious such as belt tension, hoses, Impeller etc. The final fix was removing the HX and cleaning it out, let it sit overnight in a bucket filled (per Ron's suggestion) in Lime away mix. Then flushed it clean installed it and no more over heating, running a consistent 160 degrees.
I don't believe you can adequately clean the HX by only removing the end caps, most of the little Small holes in the inside flanges were closed up.

Ron Hill · July 01, 2022, 01:52:59 PM

Dan : You can do what Bernd did, but leave the HX in place.

Take the exhaust hose off the raw water pump. Hold it higher than the HX and slowly pour Line-a-way into the hose. Hold it for about 10 minutes and then do the same again. It will dissolve the deposits and help clear the inside piping of the HX. I do that every couple of years as simple Preventive Maintenance!!

a few thoughts

dhagen · July 02, 2022, 01:57:45 PM

I replaced the thermostat. It was not the problem. When I opened the manifold, it was dry, even though the expansion tank still had coolant. So I filled the manifold and did some other work. Awhile later, it was empty again. It turns out it is leaking into the bilge. I believe it is from the 1-1/8" wire reinforced hoses to the thermostat and the heat exchanger, which are original. I've decided to change out all the hoses to prevent future problems, since they are all 20 years old.
I do have a couple of questions:
Why was there no coolant drawn out of the expansion tank? That hose is good. The fitting at the manifold is clear. I can't tell where it the passageway goes from the hose fitting entering the manifold at the pressure cap to see if that is plugged. Should it be open all the time?
Second, does anyone know how long the hoses are from the engine to the water heater?
Thanks

KWKloeber · July 02, 2022, 04:35:12 PM

Quote from: dhagen on July 02, 2022, 01:57:45 PM
I replaced the thermostat. It was not the problem. When I opened the manifold, it was dry, even though the expansion tank still had coolant. So I filled the manifold and did some other work. Awhile later, it was empty again. It turns out it is leaking into the bilge. I believe it is from the 1-1/8" wire reinforced hoses to the thermostat and the heat exchanger, which are original. I've decided to change out all the hoses to prevent future problems, since they are all 20 years old.
I do have a couple of questions:
Why was there no coolant drawn out of the expansion tank? That hose is good. The fitting at the manifold is clear. I can't tell where it the passageway goes from the hose fitting entering the manifold at the pressure cap to see if that is plugged. Should it be open all the time?
Second, does anyone know how long the hoses are from the engine to the water heater?
Thanks

Dan

Coolant is drawn back into the manifold from the overflow/reservoir tank when the engine cools down, and the coolant contracts and creates a (slight) vacuum in the closed system. If there's a leak ANYWHERE in the closed system then that vacuum cannot form and no coolant is drawn from the reservoir.

The hose to the overflow/reservoir tank is always open at the neck of the pressure cap -- there's a check valve in the pressure cap that lets coolant get sucked back from the overflow/reservoir tank into the manifold neck when the slight vacuum forms, but prevents coolant from going out from the manifold to that hose when the closed system is under pressure (12-15 psi.)

If the closed system overheats and pressure builds to above the pressure cap rating then expanding coolant gets pushed into the overflow/reservoir tank via a different (spring-loaded) valve in the pressure cap.

https://www.google.com/search?q=how+does+a+radiator+pressure+cap+work

Did you pressure test the Hx? Coolant can go to the bilge of the end cap is leaking, or out the exhaust if the (a) Hx has a pinhole or (b) manifold exhaust flange gasket is bad. Or in another scenario coolant can go into the closed potable water system if the water heater Hx has a pinhole.

Stu Jackson · July 03, 2022, 11:44:21 AM

Quote from: dhagen on July 02, 2022, 01:57:45 PM

>>>>>>>>>>>>>>>>
Second, does anyone know how long the hoses are from the engine to the water heater?
Thanks

From Critical Upgrades (a VERY important topic)

https://c34.org/bbs/index.php/topic,3769.0.html

Ron Hill · July 03, 2022, 02:03:31 PM

Dan : You need to change out all of the engine hoses that are painted the same color as the engine!!!

Just remember that all hoses on the suction (inlet) to a pump need to be wire reinforced. Also all hose that make an acute turn need to be wire reinforced. All other hoses can be nylon reinforced and can be purchased at an auto parts store!!

A few thoughts

dhagen · July 03, 2022, 06:09:29 PM

Thanks all. I can see coolant leaking from above the heat exchanger. I believe it is from the 1-1/8" hose painted gray that goes into the heat exchanger. Also the 1-1/8" hose from the manifold to the thermostat is shot. I will start by replacing those. Once those are replaced, maybe the coolant overflow tank will work properly.