200hp Mercury Overheating

[winstontj]

Hi all, New here and new to mercury 2-strokes so please forgive my basic questions.

I am a volunteer at a local boating center and because I know about car motors they assume I know about outboards as well.

The boating center has an 80's vintage (will get SN and year and post) V-6 Mercury 200, its a V-6 with three carburetors, black square cover.

It is overheating. Boat was donated - condition unknown and TOTALLY unknown to me. Starts, runs & drives fine - but overheats. Impellor and water pump were changed and it still overheats.

Where can i find the temperature sensor? What temp should the outside of the block be on an infared heat gun? Could a loose wire cause a faulty signal?

I have not yet pulled the plugs or started the motor. Can anyone provide some words of advice before I start taking things apart on this? I fear its a head gasket but don't want to just tell that that without knowing for sure.

What compression #'s should I get if I do a comp test?

Thanks all... OH anyone in Boston know anything and want to help? its volunteer work so the best i can do for you is pay you in beer

 

[hkeiner]

Re: 200hp Mercury Overheating

It is overheating. Boat was donated - condition unknown and TOTALLY unknown to me. Starts, runs & drives fine - but overheats. Impellor and water pump were changed and it still overheats.

If you are certain that it is overheating, then using a water pressure gauge can be an effective way to troubleshoot this. Installing a water pressure gauge is easy to do and not very expensive. The below guides may be of help.


http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49

 

[Irv964]

Re: 200hp Mercury Overheating

If you are certain that it is overheating, then using a water pressure gauge can be an effective way to troubleshoot this. Installing a water pressure gauge is easy to do and not very expensive. The below guides may be of help.


http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49

Great info/link hkeiner, I was enquiring about how to install a water pressure gauge in another post and never received an answer. I have already saved it in my favorites!
Another question, last week-end while anchored I pulled a large amount of seaweed up from the bottom and later I noticed some had gotten into my water inlet/intake port on the starboard side. I pulled it out carefully but I am not sure I got it all (it was only in 1 of the 4-6 vents) My pee'er still felt strong and the water was warm so can I assume I got it all? It is a 2007 90hp Merc 4 stroke.
Do you think the pressure gauge will be an easy install on this motor? Also, where does one purchase these kits? Thanks in advance and thanks for sharing your info........Irv964

 

[hkeiner]

Re: 200hp Mercury Overheating

Do you think the pressure gauge will be an easy install on this motor?

I am not familiar with your particular motor layout but in general as long as you can identify the correct hose to tap into with the T-connector, it should be no more difficult than on any other motor. The only challenge is to route the tubing from the T-connector all the way to the dash where the gauge is installed.

Also, where does one purchase these kits?

You can buy them here on iboats (preferred), on ebay, a local boat shop, or you can do a search on the internet to find a variety of sellers. A good search term would be "water pressure gauge kit".

 

[Irv964]

Re: 200hp Mercury Overheating

Thanks hkeiner, I will be sure to look here first for the gauge. Hopefully it is an easy task on my motor?
What is your take on that piece of sea-weed I mentioned? I have no idea how much got in, if any for that matter. Would the impeller more than likely chew that up? It was the real fine slimy sea-weed if that makes a difference? Thanks for your help!.........Irv964

 

[hkeiner]

Re: 200hp Mercury Overheating

What is your take on that piece of sea-weed I mentioned? I have no idea how much got in, if any for that matter.

My take would be that the seeweed did not clog things up enough to cause the overheat condition, but this is only a guess. You can try checking things out by removing the lower unit and inspecting the water pump housing and impeller and while dismantled, you can try runing some water through the intake toward the water pump area using muffs to see if the flow looks good. If it were my motor, I would first install the pressure gauge and see what the gauge readings indicate before taking things apart. A water pressure gauge kit costs about $50.

 

[winstontj]

Re: 200hp Mercury Overheating

Thanks for the replies. I'm not 100% certain that its overheating. I'd like to check the gauge on the console as well as the temp sensor and this other water relief valve I've seen mentioned - but I know nothing about them or how to test/where to find them.

Where are the temperature sensors located? Can I remove them, place in hot water and test the resistance?

 

[hkeiner]

Re: 200hp Mercury Overheating

You can also use temp sticks or an infrared thermometer to independently check if the motor is overheating and confirm that the temp gauge on your dash is accurate. If these tests confirm that the gauges/senders on your motor are accurate, you won't have to do the more complicated bench tests to confirm their accuracy. Please note that the temperature measured on the suface of the motor block (with the temp stick or IR unit) will not be exactly the same termperature as reported by the sender/gauge on the boat, but it will be close enough for testing purposes. Just my thoughts...

http://www.iboats.com/Thermomelt_Te...8555994--**********.806358773--view_id.366448


http://www.google.com/products?hl=e...&lnk=pruser&hl=en&price1=20&price2=30&btnP=Go

 

[j_martin]

Re: 200hp Mercury Overheating

Thanks for the replies. I'm not 100% certain that its overheating. I'd like to check the gauge on the console as well as the temp sensor and this other water relief valve I've seen mentioned - but I know nothing about them or how to test/where to find them.

Where are the temperature sensors located? Can I remove them, place in hot water and test the resistance?

It sounds like you're getting pretty involved with this machine. It would help a lot if you got an OEM service manual for that engine. Most if not all your questions are answered in the manual. Basic procedures for testing components, and troublshooting problems, such as overheat are also there.

To answer the question, there are two sensors on it. One on each head. One has two wires to it, and is a temperature gauge sending unit. The other has one wire going to it, and is a snap switch set to trip at about 240 degrees, grounding the wire going to it and sounding the alarm buzzer in the controls. Other than that, they look similar, and mount in a similar fashion.

hope it helps
John

 

[sonnet]

Re: 200hp Mercury Overheating

I may should have started a new thread but I have a 90 model 200 Mercury outboard OC serial # that overheats and has low water pressure. I have lowered it further and further in the water and Still it will get hot when running all out 5600rpm or so.
I have changed the waterpump housing and lower O-ring as well as the plate impeller, thermostats and am checking the poppet valve now.
Question: Does the poppet valve come out of the block from the outside?
I was attempting to verify that it was not stuck open...the diaphram was flush with the powerhead so I guess it is not stuck open...
I guess the next step is to replace the diaphram and outer housing gasket and see if things change. My water pressure never gets above 5 or so and I have a new guage and line ran back to the motor and teed at the port where comes from the block. Any suggestions would be appreciated as I am unsure about some of this to say the least...

 

[hkeiner]

Re: 200hp Mercury Overheating

I suggest that you start a new thread. You will probably get more replies that way. Many forum posters may not read through a long thread to see that a new question has been posted.