Changing thermostat on 4.3MPI

[TexasA&M]

Was at the dealer today to pick something up from them, so I figured I'd get a new thermostat since mine is stuck open. The thermostat alone was $25, and didn't come with any gaskets, so I passed it up to try and find it somewhere cheaper.

Auto thermostats are only a couple of bucks, and I can't imagine that the marine version is any different.

Who here has replaced the thermostat before? Where are you getting parts? Anything difficult about the job?

FYI, I've got a 2005 185 Sport, with 4.3MPI.

Thanks for the tips.

- Steve

 

[Presentation]

Step #1) Get your engines serial number. This is on the engine cover, that plastic thing over the flame arrestor.

Step #2) Go to the official Mercury website http://www.mercurypartsexpress.com/us/ and click on “Part Search by engine serial number” then find the parts you need, print any schematics you need.

Step #3) Google the parts to find the best prices.

Substitute automotive parts at your risk.

 

[TexasA&M]

Sweet. Thanks for the tip on searching by serial #. I'll give that a whirl when I get home tonight.

 

[midway]

I have an o4 carb version of the 4.3L, I pulled and cleaned mine twice before replacing it. Trash from the water gets caught in it and holds it partially open, engine will not heat up then to open so trash falls out. I did replace it finally and have had to clean the new one out twice since.

 

[Presentation]

I have an o4 carb version of the 4.3L, I pulled and cleaned mine twice before replacing it. Trash from the water gets caught in it and holds it partially open, engine will not heat up then to open so trash falls out. I did replace it finally and have had to clean the new one out twice since.

Just to explain this, you remove the thermostat as you normally would to replace it.

Somewhere here I typed a step by step guide with schematic for a 5.0L engine on how to replace a thermostat.

Next you heat a pot of water on the stove. You dunk the thermostat into the water until it opens.

By the time the thermostat diaphragm opens the water is very hot.

Once the diaphragm on the thermostat opens remove the thermostat from the pot, don’t use your hands, use a tongs or some other kitchen utensil that will really upset the wife. You are already invading her space using her stove and her pot so do it right and use the fancy tongs she only uses on Thanksgiving and only with her family, not yours.

Now take a small metal pointy object like a spark plug gaping gauge or since you are in the kitchen and you found the kitchen utensil drawer, grab a a nut picker and scrape the edge of the thermostat that is now exposed with the diaphragm open. It’s a process similar to what I think the dentist does inside my mouth but I’m not a dentist.

Rinse the thermostat under cool running water and see if it closes all the way. If the diaphragm closes all the way tight you are done. If not, repeat the heat water, dunk thermostat, remove, and scrape process.

In my opinion; the correct way is to replace the thermostat with a new one. The reason to do the above is if you have an engine that just takes forever to get warm and you don’t have a spare thermostat available at the time.

Cleaning and reusing a thermostat is like cleaning and reusing your marine head's duck valves or using a coat hanger to hold your muffler on your car. I’ve done all three due to not having the correct parts on hand, or fifty cents for a clamp in the case of the muffler on my car when I was in college, but all three are considered temporary fixes or "Jonnie rigging." Its like being a ghetto macgeiver.

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[quailrunner]

Several descriptions on the web indicate that marine thermostats open at lower temps that auto, and that the materials used to make them may be different. I know that my mechanic gave me a long lecture when I asked what the difference was between a marine impeller and the ones used in cars.

 

[Presentation]

Several descriptions on the web indicate that marine thermostats open at lower temps that auto, and that the materials used to make them may be different. I know that my mechanic gave me a long lecture when I asked what the difference was between a marine impeller and the ones used in cars.

Some things I will substitute automotive parts due to availability or cost, some things I will not. I don’t tell others to substitute, it’s their business.

An example of an item I will substitute an automotive part on my marine engine is a serpentine belt. When I can replace a Mercury serpentine that would cost me $120 with shipping Mercruiser # 865615Q03 and instead buy a Gates K061066 for $23 with shipping from Amazon.com I do it .

 

[TexasA&M]

Pulling up an old post here, but I finally got around to buying a new thermostat today. Any tips on pulling the housing apart? I haven't been able to find any stop by step directions online, but it should be pretty straightforward. Any/all tips are appreciated.

 

[flarepoman]

Texas try this next time. And the thermostats are not the same as a car one.

http://www.ebasicpower.com/pc/OSCMC552-SB/MER8B-IB/Thermostat%20Base,%20Mercruiser%20GM%20262%204.3L%20V6,%20305%205.0L,%20350%205.7L%20V8%20GM%20Center.html

 

[TexasA&M]

Thanks for the link. I picked up the 160* thermostat kit for $31 after tax. The site has it for $22.95, but shipping to Texas is $13, so I got a better deal this time. Still WAY too much for a $3 automotive part, but that's life on the water. Hopefully it is as easy as changing the thermostat on an auto..............

 

[TexasA&M]

Aight, I got the thermostat changed out... pretty straight forward, although I did scratch my head for a second trying to figure out how to get the tstat out of the housing.

The old one was definitely stuck open by debris. The new one is much prettier too! Not sure if this will solve my intermittent alarm, but I'm not getting my hopes up.

Question: There are two sensors in the housing. One is temp, and I assume the other is flow. How does this sensor work? I didn't remove it, but I looked at it as best I could, and I don't see how it could get clogged. I'm wondering if my alarm is being sounded by this sensor for some reason?

Also, I found a loose ground wire in the bundle that hooks to that sensor. It was obviously never hooked up to anything, but I went ahead and grounded it to the manifold anyway.

There is a diagnostic port in this bundle as well. Is there any way to use it other than having a tool?

One final thought... I only needed one of the many gaskets that were included in the $35 kit... next time, I'll be buying a $4 automotive thermostat, and a $1 gasket.

 

[Fun Times]

The old one was definitely stuck open by debris. The new one is much prettier too! Not sure if this will solve my intermittent alarm, but I'm not getting my hopes up.

Because your thermostat had debris then there's a chance that your water PSI sensor is seeing a low PSI as well sounding your horn do to the debri in the intake water flow system someplace.

Question: There are two sensors in the housing. One is temp, and I assume the other is flow. How does this sensor work? I didn't remove it, but I looked at it as best I could, and I don't see how it could get clogged.

The other sensor you see in the T housing is not a water PSI sensor, They are both water temp sender/sensors, One to the helm, And one to the engines ECM unit.

I'm wondering if my alarm is being sounded by this sensor for some reason?

Only if the sensor was reading hot for some reason.

Also, I found a loose ground wire in the bundle that hooks to that sensor. It was obviously never hooked up to anything, but I went ahead and grounded it to the manifold anyway.

The ground wire goes to nothing really, at least on your engine set up anyways, But you did not hurt anything by hooking it up either.

There is a diagnostic port in this bundle as well. Is there any way to use it other than having a tool?

No sorry, not at all.

One final thought... I only needed one of the many gaskets that were included in the $35 kit... next time, I'll be buying a $4 automotive thermostat, and a $1 gasket.

I highly recommend that you do not do that next time, The gasket between the housing and the intake manifold needs the rivets for grounding purposes so the sensors will work correctly, And the thermostat is stainless steel, That is one reason why it is more $$$.

Your water PSI sensor should normally be on the power steering cooler.:thumbsup:

See number 17 in this link below.
http://www.mercruiserparts.com/Show...8550&bnbr=260&bdesc=Power+Steering+Components

 

[Daniel P Thomas]

Presentation

Thanks for the link for part look-up by serial number.
Could not understand why I had 2 different temp thermostats when I pulled them to winterize.

One was a 160 and one was a 140 degree.
Only place I could find correct info was through your link!
As there are a new and an old configuration for the t-stat, housing and related hoses.

Thanks
Dan

 

[TexasA&M]

Because your thermostat had debris then there's a chance that your water PSI sensor is seeing a low PSI as well sounding your horn do to the debri in the intake water flow system someplace.

The other sensor you see in the T housing is not a water PSI sensor, They are both water temp sender/sensors, One to the helm, And one to the engines ECM unit.

Your water PSI sensor should normally be on the power steering cooler.:thumbsup:

See number 17 in this link below.
http://www.mercruiserparts.com/Show...8550&bnbr=260&bdesc=Power+Steering+Components

Excellent info!!! I was thinking that I could be getting a low flow reading as well since the thermostat never closed... I'll cross my fingers and hope that the new tstat does the trick. Unfortunately, it may be a while before I get back on the water to test it.

That second sensor sure did look like a temp sensor, so I'm glad that you confirmed that. Makes sense that there are two... I like having an old school gauge that doesn't run through the computer system.

In regards to the water flow sensor/power steering cooler... where exactly is that located in the engine bay?

 

[TexasA&M]

I highly recommend that you do not do that next time, The gasket between the housing and the intake manifold needs the rivets for grounding purposes so the sensors will work correctly, And the thermostat is stainless steel, That is one reason why it is more $$$.

Even so, I should be able to get the correct marine tstat and gasket for less than $30... no need to buy the whole kit.

 

[flarepoman]

Some things need to be marine grade,like thermostat's gaskets.

If someone cannot afford something as little as that they should sell the boat. I don't get it.

Boating costs!!!! no getting away from that.:huh:

 

[TexasA&M]

Fair point, but I see no need to spend money on 5 other gaskets that are not needed and I will only throw away. I'd also say that at least part of the time, the only difference between 'marine grade' and standard auto is the price.

Boating doesn't ALWAYS have to be expensive... If I had a ton of money, I'd have a bigger boat and just let the dealer work on it. I don't though, so I have to save where I can; working on it myself and saving money on parts. $15 goes a long way at my house, so if I can save $15 without sacrificing safety or functionality, you can bet I'm going to do it.

 

[Gunn]

An example of an item I will substitute an automotive part on my marine engine is a serpentine belt. When I can replace a Mercury serpentine that would cost me $120 with shipping Mercruiser # 865615Q03 and instead buy a Gates K061066 for $23 with shipping from Amazon.com I do it .

Where did you find the cross-reference on belts?

I'd like to change out a serpentine built on my port engine, but I have the 4.3. From your link to mercruiserparts.com, it looks like my part # is 57-865615Q04 instead of Q03 like yours. $86.27...

Tom

 

[Chipshot]

Take your OE belt number to your local NAPA Auto Parts store and they can interchange it for you. NAPA belts are made by Gates btw.

 

[TexasA&M]

UPDATE:

Finally got the boat out on the water for the first time since changing out the t-stat. Engine warmed up just like it should and ran great all day. Best of all, no more alarm! Ran wide open with trim as far up as needed, and no trace of an alarm. Hopefully it will be a long time before I hear that constant beep again..............