Yanmar SB8 Overheating Problem

[stollo770]

Hello,

I own a 1979 Hunter 27 with a Yanmar SB8 engine in it (hours unknown). Recently the engine has been overheating and I have no idea why. The engine starts up and runs fine for about 10-15mins or so but then starts to smoke out of the handle used for cleaning the oil filter. If the engine is left to run for another 5 minutes smoke becomes visible from the oil filler cap and is very thick. The smoke is whitish blue in color and is also visible in the exhaust. I am aware that this is from the oil vaporizing from the extreme heat within the engine and on one occasion, after turning off the engine, I could hear the oil boiling in the pan. I also managed to remove the oil filler cap and saw the same whitish blue smoke coming up from inside it.

I have already performed matiainence on the varous possible overheating causes. I have changed the impeller, made sure my raw water intake was clear, changed the oil (currently running SAE 30), and made sure that nothing was obstructing my exhaust pipe. Nothing worked, and the engine is still overheating. Whats weirder about this is my exhaust is perfectly normal right up until the whitish blue smoke appears. The exhaust water is clear, plentiful, and the exhaust gases are also clear (until the smoke starts). Also, no warning lights of any kind come on. I think they must be broken because one day the engine got so hot that it stalled out right in the middle of the bay. I figure that if the engine is so hot it stalls, then atleast the c.w. max temp light would be on, and if the oil is boiling then the oil pressure light should also be on.

Anyways, im completely out of ideas as to what might be causing the overheating. Tomorrow I will attempt a final Hail Mary at resolving this issue; I plan to remove and clean the oil filter and change the oil down to SAE 20. I figure the oil filter must have some cloggs that are impeding oil flow and causing heat to build up, and I also figure that a thinner oil will circulate around the engine better which will help to further reduce heat. If this doesnt work then its off to a marina to have a mechanic look at it. However, mechanics are expensive and if I can fix this problem myself then I would prefer to. So does anyone have any ideas or suggestions for me? Has anyone also had this problem and remembers how they fixed it? Ill take any and all suggestions.

Thank you for your time,
-Stollo770

 

[kloudie1]

Thermostat clear and functioning? Open the housing on the back of the engine and check the thermostat; it may not be opening and forcing the water through the block.. it may be bypassing all the water straight out the exhaust.
I would not go to a 20 wt oil you may not have damaged the engine yet but if you go with a lighter oil, you will most likely do that if it overheats. The noise you heard was probably water boiling inside the block and not oil.. Pull the zincs and make sure they aren't blocking a passage.. Good Luck.

 

[Bill Roosa]

Yea, like kloudie1 says thermostat. Just pull the thermo housing off remove the thermostat and reinstall the housing without the thermostat. Start the engine and if she does not over heat that is your problem. you could also test the thermostat on the stove with a thermometer in a pot of water but you have to know what you are looking for as the thermostat opens to determine if it is actually opening fully and not "jerking" open. Operating without a thermostat will not harm the engine but you should get a new thermostat soonest as the engine will operate at a very cool temp which is great for making carbon on stuff like rings, exhaust manifolds.....etc.
good luck

 

[stollo770]

Thanks for your suggestions. I'll avoid lowering the oil weight and I'll check out the thermostat. One question, where exactly on the back of the sb8 is the thermostat? I have never maintenced it before and have no idea what it looks like. Thanks for your help.

 

[David in Sandusky]

Raw water cooled?

Our SB8 was raw water cooled. In that case, there is no thermostat.

 

[Alan Gomes]

Our SB8 was raw water cooled. In that case, there is no thermostat.

Are you sure about that? Being raw water cooled doesn't have anything to do with whether the engine has a thermostat. My 1GM is raw water cooled and it most definitely does. Being raw water cooled does mean the engine doesn't have a heat exchanger, though.

This link shows a thermostat for the SB8 engine: https://www.frenchmarine.com/YSB-8-364 It's Yanmar p/n 105582-49200.

 

[MLampner]

I have the owners manual from my old YSB 12 as a PDF if it's of any value I can either post it here or get it to you some other way. I do know the 12 which was a very similar engine did have a stat but is been 4 years since it was pulled and replaced by a ym series engine so I am not exactly sure where you would find it but the manual would.

 

[kloudie1]

The little rubber water hose that ends in the exhaust .. It starts at the therrmostat housing on the aft of the cylinder head. I think four bolts hold it onto the head.. There may be a two bolt cover over just the thermostat.. This thermostat, like many Yanmars, is not a simple flow restrictor as in an automobile engine.. The Yanmar thermostat re-directs flow either through the block to cool the engine or through the bypass ports when the engine is cold..

 

[stollo770]

Hello,

Thank you for your help with the location of the thermostat. I found it and was able to replace it. Unfortunately the engine is still over heating. It lasts longer then it did before, about an hour now compared to 20mins before I replaced the thermostat, but it still over heats. The problem starts the same way, smoke becomes slightly visible from the oil filter cleaner handle and builds until it comes out of the oil fill cap. I turned the engine off before it died on its own but if i left it running for another 10mins it would have. I am now completely out of ideas as to what might be wrong with the engine. Any ideas would be greatly appreciated.

 

[celticwinds]

I think you need to connect a mechanical temp. gauge to the engine while you look for the problem so you can shut the engine off before it overheats. It sounds like some kind of obstruction in the water supply. Check to make sure the raw water strainer is clean. Remove the water line at the mixing elbow or wherever the water leaves the engine and measure to see if the proper amount of water is circulating through the system. If your system has a raw water strainer then it will have an element inside that could be clogged. If the old impeller had pieces missing they could have caused a clog. Does your seacock have a screen or some type of cover on it that could have any obstructions underneath the boat?

 

[celticwinds]

also remove the hoses one at a time and look for obstructions in them.

 

[MLampner]

Given the age of these engines it is also possible that there is a build up of corrosion in the water jacket as well as silt, and salt. I forget how but there are ways to clean some of this out without a complete tear down. If my memory serves me there are a couple of freeze plugs that can be removed and water can then be forced through them to dislog some of the gunk. There may also be a chemical cleaner that can be used but I would be real careful with anyho g like that given the age of the castings.

 

[kloudie1]

Stollo, next thing to try is to remove the thermostat and hook a water hose to the pipe that goes to the exhaust elbow. Plug the other hose in the thermostat housing. Remove the hose from the water pump at the block.. Have a way to control the waterhose at the thermostat housing..and .. very slowly.. open the water so it flows backwards into the thermostat housing and out where the waterpump hose connection is. This should get some gunk out of the block.. slowly increase flow from the hose to get a good clear flow out the water pump connection.. You should be able to get a good bit of flow.. once that is clear.. re-install the thermostat and hoses and test again.. Good Luck

 

[stollo770]

Hello,

Thank you all so much for your help and advice, it has been invaluable. I am pretty sure that I have finally solved the problem with my engine after days of attempted fixes. Following the advice here I checked to see if water was properly flowing through my engine block and through the thermostat by hooking a hose up to the intake water line and removing the bypass hose so I could observe water flow. I also removed the thermostat so water flow would not be impeded. When I turned on the hose water instantly came out the bypass on the thermostat, which told me that the thermostat housing was clogged or one of the water jackets in the engine was clogged. Not wanting to take apart the entire engine I only removed the thermostat housing, the exhaust manifold it plugs into, and the exhaust elbow. In the manifold that connects the thermostat to the engine I noticed two water passage ways that lead from the thermostat into the engine block; one of a small diameter and another of a slightly larger diameter. Thinking that a clog was in one of those passage ways in the engine block I sent some water through them and to my surprise, the water went through the engine with out a problem. I then turned my attention to the passage ways in the exhaust manifold leading up to the thermostat and found that the smaller diameter passage way was completely blocked and the larger diameter one was 50% blocked. The substance blocking them was a thick, tar like sand/sludge mix that took a drill bit to remove. I put everything back together after I removed the blockages and the overheating problem was totally fixed. A test with a hose revealed that water now was circulating through the engine and thermostat and after that test I ran the engine for an hour at full throttle with no problems. I even took the boat up and down my channel a couple times after that to make doublely sure. No smoke and no more overheating. Everything is fine once again (for now). Thank you all again for your help.

 

[kloudie1]

Great to hear the news, Stollo .. !
Happy Sailing !

 

[MLampner]

Great news, the YSB series were incredible engines simple, strong and reliable. The only reason I retired mine was it was badly undersized for some of the conditions we took her out in and while the sails do the heavy lifting there are the inevitable times one needed the engine and often against some of the stronger currents we encountered we could be doing 1/2 a knot.

When the ring gear lost a tooth due to an issue with the starter and we were going to need to pull it we decided it was time for it to retire, at least from our boat. While I don't miss the long slow trips against current from Cape May it was a good power plant. Some of the trips we make in this region no matter how well you plan will require fighting the current and when the wind goes soft as it does this time of year in the Chesapeake the added power can make a big difference.

 

[Nelsonhow]

Des calling?

Given the symptoms your motor might be ripe for a decaying with an acute store solution.

 

[Nelsonhow]

Sounds like you may need to descale the motor with a Descaling acid. (Boiler acid)

 

[stollo770]

Descaling acid? Where do you buy it and what brand do you recommend? What effects does it have on the engine? How do you apply it? My engine is running fine right now but if it can be better, then I'm willing to try the acid.

 

[Nelsonhow]

You need a small electric pump.

The pick up of the pump goes into a 5 gal bucket. But not right on the bottom. Maybe 3 inches off the bottom. The output of the electric pump bypasses the Yanmar water pump and connects to the Yanmar water pump putout hose.

You remove the thermostat. ( yes the Yanmar 8 haste one).
Put the the thermostat cover back in place.

Next you need a temporary hose to bring the cooling water from the back of the engine into the 5 gal bucket . This goes in place of the hose the dumps water to the exhaust riser.

Put the a it solution into the 5 gal bucket unsung the correct dilution.

Turn the pump on. The pump pushes the acid into the Yanmar block and it comes out the exhaust cooling hose into the bucket. I suggest you try it with plain water before you add the acid. There should be no leaks.

Run the pump for a few hours. You'll probably see a lot of junk flushed into the bottom of the bucket.

Then replace the a it solution with water and flush the block well. Remember to neutralize the acid as directed before you discard. Backing soda works well.

Reconnect the Yanmar pump and run the engine for a good long time with fresh Easter. Then remember to put the thermostat in and run it again for a good long time.

Don't know the connection process for a fresh water cooled motor but is should be a variation.