Mercruiser 260 Thermostat replacement

[Reorandy]

I went to replace the thermostat due to heating issues on my '87 Mercruiser 260 V8 5.7L Sea Ray, only to find no thermostat in the housing. Engine SN 0B652010. I bought #18-3651 Sierra Thermostat Kit, but there are too many gaskets and rings and I do not know where they go. I scraped off all the old gasket material off the bottom and top of the housing, but not sure where all the gaskets go. See pic of bottom housing in the boat and pic of the kit. I believe they are in order to place them on the bottom housing from left to right with gasket first, rubber O ring, thermostat, housing cover, but not sure. The other three gaskets at the bottom of the pic I am not sure if they are used. Do I need to use any gasket goop or just the way it is?

 

[84EdH]

Re: Mercruiser 260 Thermostat replacement

First things first. What kind of "heating issues" are you having? Not having a thermostat in place should not cause overheating, the thermostat keeps the water circulating through engine until about 150 degrees, then opens, lets water out to exhaust manifolds. The normal procedure is to suspect impellar first for overheating issues.

also, no gasket goo needed, but the surfaces have to be Clean. I can still see the polka dot pattern from the old gasket on the housing piece in your pic. emery cloth, steel wool etc.

 

[84EdH]

Re: Mercruiser 260 Thermostat replacement

https://webapps.brunswick.com/literature/literaturePartsInfo.do this link shows a diagram that matches up to your serial number

 

[Reorandy]

Re: Mercruiser 260 Thermostat replacement

Thanks for the info. I will try to get the surface cleaner with steel wool. I know I need to check other things to solve the overheating problem, but figured it couldn't hurt to change out the thermostat. The link said "Image not available", so I could not view it. I don't believe I need all the gaskets for the job, but still not sure which order to put the needed ones on.... I think you are right on about the impeller and I will get that changed out too....

 

[Bt Doctur]

Re: Mercruiser 260 Thermostat replacement

http://www.mercruiserparts.com/Show...r=210&bdesc=STANDARD+COOLING+SYSTEM(DESIGN+I)
Item 8 is open ,not closed as shown.

 

[Reorandy]

Re: Mercruiser 260 Thermostat replacement

Thanks. Diagram is a little hard to see for sure, but it looks like from the bottom up- the lower housing, thermostat, round brown "speckled" gasket, "sleeve", gasket and housing cover. I didn't get anything with the kit that resembles a thermostat sleeve (#7) in the pic. Just skip it? Also, what about the round rubber "O" ring that came with the kit? The O ring is not in the diagram. Also not sure what you mean by #8 (gasket) is "open".... Thanks for your ideas, I just got hung up on clarity and wanna make sure this gets in there right... Thanks again...

 

[Badfish95]

Re: Mercruiser 260 Thermostat replacement

Do not skip the sleeve. It's usually a brass sleeve that will hold pressure against the thermostat sealing it against the upper gasket and lower cork gasket. You'll want to take a small wire brush or something to the internal thermostat seat area since it looks pretty corroded. It looks like you have the right diagram. Make sure you do, otherwise you may end up blocking important passages. I just changed mine and the dealer gave me the sleeve you need. It was not right for my application so I took it back, but looks like the one in your diagram. They changed these housings up quite a bit over the years. It still gets me how many thermostats are pulled from these engines...

 

[Reorandy]

Re: Mercruiser 260 Thermostat replacement

Thanks for the input. I just assumed everything I needed to put the thermostat in came with the kit. There was no sleeve with the kit. So the correct order for things on top of the lower housing is: thermostat, round brown cork gasket, sleeve, gasket and housing cover? That's what the diagram shows, but it doesn't really appear that the seal on the thermostat would be that great this way the diagram shows. I put the thermostat directly on the housing and it had to be seated perfectly to cover the hole. Round rubber O ring is not used? Just want to be sure that I am doing this right. I was floored when the thermostat was missing when I opened the cover.....

 

[Badfish95]

Re: Mercruiser 260 Thermostat replacement

The reason your kit did not come with the sleeve, is that the parts distributor assumed you are replacing a thermostat, not installing it all over again. The sleeve could be reused if it hadn't been tossed by the PO. The "extra" gaskets/o-ring are supplied so that regardless of cooling system design(I, II, or III) you should have the gaskets to complete the job. It looks like you have design I where I had design II. Your kit would work for me if I had the correct sleeve. I would toss the cork gasket and flow through top gasket and use the o-ring where you would toss the O-ring and solid top gasket and use the cork gasket and flow through top gasket. My sleeve was plastic and had two cutouts, yours is a solid brass ring.

There is a photo of the sleeve you need in my post here:

http://forums.iboats.com/mercruiser...rottle-hestiation-question-5-0lx-611191.html?

Again, it was incorrect for my application, but is what you need to complete yours. I hope this post makes sense and helps you out.

 

[Reorandy]

Re: Mercruiser 260 Thermostat replacement

Yes it does help, thanks. I just ordered a sleeve. Thanks to all for your help. Really appreciate it!!