Temperature creep

[egaito]

We're still getting some creep after descaling our 8v92's. We're find below about 1200rpm's, but as soon as I push beyond, the temp creeps up proportionally on the stb side. I give up at 2000rpm with about 180. As soon as I slow down, the temp drops back down again.

I'm thinking, no, hoping actually, that we've got a stuck thermostat. Impellers and thermostats were replaced between 150 and 200 hours ago. It's about time for impellers again based on age if nothing else, but the thermostat is easier to get to.

Questions:

Can I run without a thermostat for awhile without doing a lot of harm, as I used to do with my cars to test the theory? Water temp here is about 80 currently, so I don't think believe it will run too cool.

If it's not the thermostat, I'll try the impeller, since it's getting to be time again.

If that doesn't do it, I guess I'm looking at heat exchanger issues, no?

Thanks in advance for any input.....

[Top Shelf]

Is that a new issue for you? My 892TAC's always run at 180 at cruise (1850 RPM). That's via IR on each thermostat housing as well.

I remember a thread here long ago about max temp on 892's at 190 or 200 and there seemingly wasn't much of a buffer between "normal" and overheat on these. But I'm pretty sure 180 is normal.

Karl or others can correct me if I'm wrong. But then again if you've been running alot cooler and this is new something is up. Thx.

[egaito]

Is that a new issue for you? My 892TAC's always run at 180 at cruise (1850 RPM). That's via IR on each thermostat housing as well.

I remember a thread here long ago about max temp on 892's at 190 or 200 and there seemingly wasn't much of a buffer between "normal" and overheat on these. But I'm pretty sure 180 is normal.

Karl or others can correct me if I'm wrong. But then again if you've been running alot cooler and this is new something is up. Thx.

It's not terribly new...we just don't push the boat hard enough, frequently enough, to get either of them to creep up, and the Stbd has always been a few degrees higher than the Port.

It is possible that I'm worrying too much. Temps on both remain steady at any given RPM, and drop down just as quickly with declining power settings. 180 just sounded high to me, and I'm not sure how high I should let them go before I begin to worry.

[chris piazza]

I don't think 180 is high. I have 892's and at cruise in my boat (1950rpm, 18.5kts) I am steady at 185. With that said I am on the great lakes and water temp hardly ever goes over 70. Right now I would be surprised if it was 50. It still will hold at 185 even in cold water.

Chris
Superior Nights 53C

[Pascal]

180 sounds fine at 2000rpm if it doens't creep any higher, does it?

didnt' you guys change the impellers recently? I recall angela borrowing my impeller puller, that was few months ago... cant' be that many hours.

if they're holding 180 at 2000, i'd leave it alone.

[Genesis]

180 is ok.

"Never exceed" is 195F. The thermostats are fully-open between 180-185.

You cannot run without the thermostats - they are a bypass design and you WILL overheat (BADLY!) if you run with them out.

If you are holding at 180F you're ok, especially with the crazy-warm raw water down there. Just don't let it go over 185F; beyond that you have NO MARGIN and will go from 185F to 195 and beyond REAL FAST.

[ron6785]

180 is normal in the southern waters, are your wheel totally clean, if fouled will go much beyond 180.

[ron6785]

180 is normal in the southern waters, are your wheels.. totally clean, if fouled will go much beyond 180.

People get nuts about changing impellers. If your props are not clean and the bottom is dirty, then she'll heat alittle. You don't seem to have much of a problem.

[SKYCHENEY]

I guess I'm nuts then.

I've never seen an impeller that's been in more than 2 years that hadn't started to crack at the base of the vanes. They are easy to change and it should be the first thing to check if you have heat issues. Also look for wear on the cover plates when you reinstall. The last thing you want is for an impeller to shred itself up and end up scattered throughout your cooling system.

[egaito]

I guess I'm nuts then.

I've never seen an impeller that's been in more than 2 years that hadn't started to crack at the base of the vanes. They are easy to change and it should be the first thing to check if you have heat issues. Also look for wear on the cover plates when you reinstall. The last thing you want is for an impeller to shred itself up and end up scattered throughout your cooling system.

OK, I'll agree with all of this EXCEPT the easy to change part! This set should come out more easily given the liberal use of grease on the shaft when installed, but the set I took out of there was a real pain, even with a puller, (which should really be called a shredder), and there wasn't enough access to tap them back in without making my own "tool" to transfer force from an angled approach.

Easier than rebuilding a heat exchanger for sure, but not easy!