87 w/ 5.7 Mercruiser - what is a typical operating engine temp?

[CobaltRick]

We ran the new-to-me DV18 (1987) for at least 5 hours yesterday and I periodically looked at the gauges to see how things looked -- everything looked fine except what bothered me -- the water temp.. The needle never seemed to leave the 120F section of the dial.. IF that was in fact about the temp it was running at that could indicate that the thermostat is wide open (or near wide open) and cooling the engine way too much..

I think I read somewhere else that they ought to run at about 160F? Is that about right for this era Mercruiser? Does this era engine have a thermostat? I'm assuming it does.

Of course it could be the case that the temp sender is DOA and the meter is just not reading anything.. Thoughts??

[akorcovelos]

‘87 Merc 260 would have a 160* thermostat, pre-‘85 had 140* and depending on where you boat the 140* might be better. Water temps by me can hit 90* so I ran the 140* on my old boat, but if you boat a cold water lake the 160* will be better.

Without a IR thermometer the best way to check (carefully) it to touch the top of the exhaust manifolds. At operating temp you should be able to hold your hand on them without getting burned, the port side will be colder than the starboard, but both should be warm, not hot.

You can also pull the two outlet hoses off the thermostat housing and make sure the check valve balls aren’t stuck, just pull on each one to make sure it opens freely.

120* seems cool, which won’t really hurt anything other than fuel efficiency, better cool than hot.

[Big Block Power]

Volvo came out with a bulletin stating to replace the 140 with a 160. Mostly because the oil was never getting warm enough to get rid of moisture in it. I change my oil every 10 hours because that's all I can put on in my garage in 1 season.

[CobaltRick]

Thanks so much guys!! I’ll look into this before I take it out again. According to my Humminbird fish finder, the water temps where we were the other day in the SF Bay Area were between 75-79F..

Hopefully I can figure out what’s going on. Thanks!

[ajcampen]

Replace t stat. Stuck open

[CobaltRick]

I did open up the thermostat housing based on where it would be on a Chevy small block and it was exactly where I assumed it would be. The gasket came out easy enough but the t-stat itself refused without a lot of persuasion.. I’m sure it’s dead now but it looks like it’s been in there for a long time.. hopefully I can snag a new one at West Marine or another boat supply place nearby. I’m also going to replace the fuel filter/separator which has a date on it from May 2017..

[akorcovelos]

Just get one from your local auto parts store, it a regular old 160* thermostat. No reason to pay the 100% markup a marina is goin to stick you with.

[CobaltRick]

It’s really that easy..? What do I tell them for engine type.. it’s a 305Cid engine.. I’m assuming the closest engine is either a ford or Chevy..

[akorcovelos]

If it's a 5.7 Mercruiser 260 that's a GM 350CI based engine. The problem may be finding an automotive one rated at 160 as most are 195 for that era GM small blocks.

Here is the Sierra kit number: Sierra International 18-3648 Thermostat Kit.
Link to Amazon: https://www.amazon.com/Sierra-Internati ... 9360124641

If you don't want to wait on shipping NAPA should stock Sierra Marine parts as well, but it will be more than Amazon, less than a marina.

[CobaltRick]

I'll check some of the local auto shops to see what they can come up with.. my thermostat (the old one) doesn't look like the one in the picture..

Mine isn't a Mercruiser 260, but a Mercruiser 230.. Not sure what that changes in the grand scheme of things. My t-stat looks like this.. and yes, this one is a bit bent up from its removal..

IMG_7669.jpg

IMG_4251.jpg

[akorcovelos]

Should be the same thermostat, the 305 and 350 share the same block. I just saw the thread title and assumed we were talking about the same engine.

[CobaltRick]

ok.. I'm back.. Yesterday I bought a replacement thermostat from a local marine store just because it was convenient and I was already getting a few other things. Its a MerCruiser part that was claimed to work with my engine. Well, the long and short of it is that the t-stat didn't seat the way the old one did and I closed it up the best I could and eventually ran the engine but it was leaking through the bolts holding things together. So, I ended up watching a few YouTube videos on t-stat replacements on these boats and it appears there's a sleeve that's either plastic or brass (Depending on age perhaps) that is supposed to hold the t-stat in place down the "throat" of the opening.. It does in fact appear that I have a brass sleeve down in mine but I've got no ideas on how to remove it... Does this ring a bell with anyone here? I found a thread with some pics associated with this.. I guess I need to find a way to remove & replace my own sleeve .. I've got no idea whether I need a cut-out on mine or not.. If there are multiple designs for my year I'll have to look into that. Unfortunately I need to spend more time on this and just haven't had a large block of time to devote to it in the past couple of days. Hopefully I can get the sleeve out and put a new one in whether its plastic or brass and whether it has a cut-out or not...

Here's the link to the other forum thread (on another site) : https://forums.iboats.com/forum/engine- ... tat-sleeve

[akorcovelos]

Mine had the brass sleeve, you should be able to pull it out with a set of small needle nose pliers. I know the housing on mine wasn’t perfectly true anymore after 30+ years so I just doubled up the gasket and it sealed fine.

[CobaltRick]

Ok.. I’m nearing the end of this task.. the problem im having is that once it’s all bolted together again, as soon as I start the engine, it starts leaking at the place where the block meets the upper water connections with the two hoses on it. I’ve tried the supplies new gasket as well as the old one.. the old one was worse than the thinner new paper one. I might try the rubber o-ring in addition to the rest even though it’s not called for.. plz let me know if this is a bad idea

[CobaltRick]

Ok.. the rubber o-ring is out.. I couldn’t figure out how to install that without leaks elsewhere unless I put it next to the cork gasket on top of the t-stat.. the only other thing I can think of would be the liquid gasket stuff in a tube but am hesitant to go that route if there’s a better way