M5411 Thermostat

Don S/V ILLusion · Jul 5, 2011

I can't think of a reason NOT to replace the thermostat. It is a regular maintenance item often overlooked and should be replaced periodically even when it seems to be performing well and especially so in a raw water engine.

There are solutions specifically intended to flush marine engines. I forgot the name or brand but it has been discussed here previously and a search on the archives would be prudent if you have not already.

You might also widen your query to more than the C30 subset of this forum as the 5411 was used in many different boats.

Anonymous 121765 · Jul 6, 2011

Sean,

The 5411 was in my 1980 C30 and in Florida conditions grossly underpowered.

I assume you are salt water cooled. If this is the case, the interior or your engine is cladded with a protectant coating to stop rust. I changed to the 3M20A in 1993.

Did you look to see if the blockage could be from the old thermostat deteriating? Over time all things begin to break down. I would change the thermostsat (do not use any teflon tape as the fitting needs a ground connection). Check your intake strainer also to ensure as much water flow as possible.

If your engine ran hot, remember that it depends also on ambient water temperature, and the sea is warming up. The fact you ran hotter could have disloged some scale and it collected in your thermostat housing.

Do these checks/changeouts and monitor how things go pal......

CR

Jack - La Paz Mx · Jul 6, 2011

We have had our C30 since 1995. It has been in saltwater its whole life. I really like the 5411 engine down here in the Sea of Cortez as it uses little fuel. I ran the sink drain to the water intake on the 5411 where with the raw water intake closed, the sink valve open, I flush the engine with a full sink of fresh water after each use. Can do this anchored out with tank water too. The boat sits unused in her slip for 7 months and before leaving her I flush the engine with fresh water including a container of radiator anti corrosive. This engine should run at 135 degree temps. You can back flush the cooling system with a hose at the slip. Replace the thermostat, check the water output at the stern, it spurts after warmed up. The cooling water is recirculated. Steam coming from the stern is common with this engine (specially here in CA with 50 degree sea temps), but as long as the engine temp is 135 degrees not a problem. The steam is a result of the point of water injection into the exhaust system. This location will become clogged over time due to the seawater injection and may need to be replaced (can cause reduction in water flow in cooling system). Replacement is easy, ordinary plumbing piping.

jrowan · Jul 6, 2011

I assume that all the C 30's with the 5411 like mine are plumbed the same. Mine also runs at about 135 to 140 degrees normally. If I leave the valve open that runs to the thermostat cooling water discharge pipe, it allows the cooling water to flow directly back into the raw water intake line, & circumvents the water muffler discharge end. This allows water to never flow peoperly out of the exhaust, which always made me nervous, as I'm used to seeing a steady stream out the transom exhaust as it does on all diesels. If I close the valve to the thermostat intake, water flows normally through the engine, then through the exhaust manifold, the riser pipe, then out through the exhaust as its supposed to. I've had two diesel mechanics look at it, & both agree that it's o.k. to run it this way. The thermostat just allows the motor to heat up more quickly to operating temperature by sending the raw water that went through the block back through to the impeller intake again. But in my 5411, water never flows out properly through the exhaust of this line to the thermo is left open.
I worried that the exhaust muffler begins to overheat when it isn't getting enough raw water cooling. As the last post mentioned, it's prone to creating vaporized steam from the exhaust end. Try running without the thermo & see how it runs. I guarantee it will run cooler. Also, if the thermo is removed it's less likely to catch debris & cause a potential blockadge. The thermo would only be needed in really cold temps. In summer the 80 + degree water temp. keeps the engine running at about 140 for me all summer long. Just my 2 cents worth.

Twice Around · Jul 7, 2011

My step-father's 5411 runs at 150 degrees...his doesn't pump (hardly any) water out the exhaust until the t-stat opens..everyone always worries about it when they see the engine running and only steam coming out. It has not overheated anything in 20 years, except when I forget to open the raw water intake.

Maine Sail · Jul 8, 2011

sean0965 said:
Thanks all for the interesting replies. I've order another thermostat for (GULP) $86 at Catalina direct. I'm going to try to run the engine without the t-stat now that the Maine waters have warmed up little bit. Stay tuned.

Sean,

You're probably due for a thorough cleaning of the engines cooling passage ways. Rydlyme is a great product for this. Those engines really should not run much above 140f or so or the salt can drop out of suspension and clog the cooling passages.

You'd need a cheap 12V pump that can handle Rydlyme for about an hour +/-. Harbor Fright pumps will usually suffice. You'll need to remove the t-stat so you can circulate the Rydlyme concentration from a five gallon bucket and back to the bucket for a decent amount of time.

Here's a pic of the process on a FWC engine.

HX was removed and the HX supply & return hoses used..

Maine Sail · Jul 8, 2011

sean0965 said:
Thanks Maine. I always worry about driving fluid back into the exhaust manifold and into the cylinders. How do I prevent that from happening?

Pull the hose off the injection elbow and use that as the return to the bucket... For your engine it is simple, remove impeller, or start after the RWP, pull the t-stat and circulate...

Stu Jackson · Jul 9, 2011

sean0965 said:
Thanks all for the interesting replies. I've order another thermostat for (GULP) $86 at Catalina direct. I'm going to try to run the engine without the t-stat now that the Maine waters have warmed up little bit. Stay tuned.

Sean, gulp is right!!! Can't you get a new thermostat from a Kubota tractor dealer? My local Universal dealer wanted $43 for a T stat for our M25. I bought one for $16 from a local tractor dealer. I actually bought two and came out ahead of the game.

I Googled Kubota dealers. Or use www.tractorsmart.com. Or use the Kubota website and find local dealers. Even if you can't find someone close to you, they can ship them to you --- from anywhere!!! Don't forget to order the gasket while you're at it (if you have a gasket, I'm sure one is needed, but don't know your engine.)

Anonymous 121765 · Jul 9, 2011

Guys,

When Westerbeke bought them out, all the prices tripled.
Everything now goes R B Groves in Miami........

CR

Maine Sail · Jul 13, 2011

sean0965 said:
Anyone know the typical flow rate GPM for the oberdorfer pump on a M5411? I haven't yet had a chance to flush the engine as Maine suggested above. I did however receive my pricey new T-Stat from Catalina direct.

Before installing the new T-Stat I was curious to see how much flow came out of the engine while running at idle speed. I blocked off the recirc line outlet on the t-stat and started the engine and idled ~1200 rpm. I thought water would be shooting straight up out of the T-Stat housing....it was just kind of bubbling out......I'd say at most 1 gpm. That seemed a bit low to me. I was expecting like 6 gpm. If there is significant blockage in the engine/manifold will there be that much slippage/bypass in the impeller vanes? I opened the pump and the impeller looked fine. Any thoughts? I'm definitely going to order the pump from harbor freight and start flushing as Maine had suggested.

I put the new T-Stat in and everything seemed to be working as I've always experienced. Engine would run around 150F +/- 5F.

Sean,

I have seen these pumps suck a five gallon bucket empty in about 45-60 seconds depending upon the RPM, so 5-6 gallons per minute is within the reasonable range. If you pinched the bypass and remvoed the stat it should have been flowing pretty hard..

If your engine is running at 150F you'll be likely clogging the cooling passages with salt sooner than you want or need to. This engine should run closer to 140F than 150F.

If you want less expensive stats take the one you got from Catalina direct over to NAPA and have them match it up. Should be about $6.00 - $18.00. There are only a few t-stat manufacturers out there. I've never not had them find me the stat I needed, except for those funny looking Yanmar RWC stats.

Gowen Marine in Portland often has Rydlyme in stock. I also keep some on my shelf but have less than 2 gallons right now......