SailNet Community - Reply to Topic
Thread: Yanmar coolant light on Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

  Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below

  Topic Review (Newest First)
03-28-2014 05:40 AM
Re: Yanmar coolant light on

Make seven more brief posts on this or other threads to get your post count above 10 then take a few pictures and post them. Somebody on here will recognize the engine.
03-28-2014 01:53 AM
Re: Yanmar coolant light on

Thanks very much! I have had someone look at it and not only did he come to the conclusion that it is the thermostat but also that it is not in fact a YSE8. It is a vertical cylinder as opposed to a horizontal. All YSE are horizontal. The next problem was finding out exactly what type of engine I actually have!! It turns out it's not a 1GM, and it looks like a SB or a SVE. Problem is we can't tell if it's an8 or a 12 horse power or whether it is an SB or the earlier SVE. As I now also need a cylinder head gasket and an exhaust manifold gasket I am not sure which parts to order as I am not sure exactly which engine it is and whether the parts will be the same or not. Frustrating!!
03-17-2014 06:56 PM
Re: Yanmar coolant light on

Raw water cooled Yanmars generally have alarm temps of about 120F. This is below the temp to damage parts if action is taken to shut the engine down. Long term operation above about 140F will cause plating of salts on heat transfer surfaces. Action is needed to prevent further increase in temp as engine damage will occur if action is not taken.

I am not familiar with the construction and specific instrumentation of the YSE8 but I am familiar with other small raw water cooled Yanmars and offer that I would investigate three things in the first troubleshooting -

First I would remove the thermostat and test it on the stove. Put it in a pan of cold water with a cooking thermometer and turn the stove on and check to see that the thermostat opens when the temp of the water approaches 110-120F and is fully open by about 130F. If you have or can get the expected exact values for your engine use those temps instead. Then take the thermostat out of the pan and run cool water over it and check to see that it closes. Drop the thermostat back into the pan and check that it opens again...repeat as needed to convince yourself it's operating normally.

Check the thermostat when you remove it to make sure that it is not fouled preventing flow.

Second I would check the water pump impeller - inspect and replace it if needed. Check for dry rotting of the rubber/plastic vanes and for missing vanes that could be blocking passages. Even if you are seeing flow out the exhaust with the engine running the flow rate could be too low due to damage to the impeller or blocked passages.

Third I would remove the temp sender for the alarm and heat it with a hot air gun (being careful not to overheat the plastic parts) while checking the switch contacts to make sure they are opening and closing normally. If the contacts seem to operating normally you can heat a pan of water to measured temps to check the opening and closing points of the sender.

If this is found to be normal I would pull the exhaust manifold and clean it.

Hope this helps. Good luck.
03-17-2014 04:29 PM
Re: Yanmar coolant light on

I had to replace my sensor unit on the mixing elbow area with similar symptoms, but a fresh water system. I would unplug the sensor unit/temperature sending unit, and see if it solves the problem upon start up, while the engine is still cool.

If you are concerned about overheating, feel how hot the mixing elbow and the exhaust water is with your hand while it is running. You might also check the engine temperature with an infared thermometer.

If the engine is overheating, how is the water flow out of the exhaust on the transom? Is it normal or impeded? If impeded, perhaps your system needs to be back flushed with fresh water. Check your impeller and water pump to see if the front end is functioning properly. You might also have a clogged raw water intake.
03-17-2014 04:19 PM
Re: Yanmar coolant light on

I had a similar problem. It ended up just being a bad thermostat. The thing was stuck open, so she started up, the coolant in the reservoir just dumped into the closed water system. The alarm wouldn't go off until the temperature was high enough for the coolant to actually be needed. Hope that helps

Sent from my iPad using Tapatalk
03-13-2014 07:03 AM
Re: Yanmar coolant light on

Hate to ask this, no disrespect meant, but are we certain it is the temperature alarm and not the oil pressure alarm? Those lights on the older Yanmars can be hard to differentiate from each other!

03-13-2014 06:32 AM
Re: Yanmar coolant light on

I am no mechanic... if it were my Yanmar 3jh2e I would verify the coolant was full via the pressure cap (when cool) and the reservoir tank had enough coolant. The opaque reservoir tank should be marked full and low. I would also verify the sending unit connections and ground were secure and clean. I would also check the sending unit unlikely it goes bad but may need a cleaning. If still having problems would consider flushing the system and installing yanmar recommended 50/50 coolant. IMHO use only Yanmar parts and products on your engine. I would also get, if you do not already have, the service and parts manual specific to your Yanmar. There are a lot of good sources online. I am a new customer to Merri Mar Yacht basin inc. in Newburyport MA for Yanmar parts. Torrenson Marine is another good source for parts and products.
03-12-2014 11:24 PM
Re: Yanmar coolant light on

Hey thanks for your response. It's raw water cooled. I have recently made a big trip on it where I had the engine running for hours on end and had no problem except on one occasion when I turned it I the light and alarm stayed on for a few minutes and then stopped so I thought it wouldn't be an overheating issue as it was in the beginning before it gets hot. However the last time it happened it came on after being on for five minutes so I got worried it was over heating and turned it off. I only bought the boat a few months ago so haven't myself flushed the coolant. The history of the boat shows that the previous owner had it serviced on an annual basis. I am a first time boat owner so am lacking in knowledge with this sort of thing, I don't even know how to flush the coolant!! Thanks again for taking the time to respond. If you have anymore ideas as to what I could do it would be much appreciated.
03-12-2014 10:45 PM
Re: Yanmar coolant light on

Raw or fresh water cooled? Could be your sender is bad (not likely) or you've got a short somewhere...or worst case scenario, you're actually overheating. There may be scale in your heat exchanger, your impeller could be bad, the coolant could be gelling up in your passages.

When was the last time you flushed your coolant and/or had your exchanger cleaned/replaced?
03-12-2014 08:09 PM
Yanmar coolant light on

Hey there! I have a compass 28 with a yanmar YSE8. A couple of times when I have started it the coolant light and alarm have stayed on. After a few minutes it stopped again but I knew something was up. Recently I went aboard just to let the engine run for a bit and it started normally with the light and alarm going off as soon as it started but after running for about 5 minutes it came on again. This was the first time it has done so after being running for an amount of time. Water is running out the back as usual so not sure what is wrong!! Can anyone help please? Thanks!

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

For the best viewing experience please update your browser to Google Chrome