Operating temp for Mercruiser 165 L6?

Guys, I got to run my boat all week while vacationing on a local lake and got to wondering what the proper operating temp for my engine should be. It idles about 140 but on a 25 mile cruise at 30 mph @ 3,000 rpm the temp steadied at a hair over 160. One thing that had me concerned after my fairly long cruise was that now at WOT I am getting some spark knock and the temp will spike to 180 just a few seconds after the spark knock is heard. As soon as I heard the spark knock I backed off to a lower speed and the temp came back down. It still idles at 140 but runs rougher than before.

This had not happened on WOT before the 25 mile cruise. Before it would run smooth as silk for a few minutes at WOT 4,300 rpm/42 mph (gps) without any sign of spark knock. The engine is now idling a little rough and has me wondering if my timing has slipped a little advanced. The distributor feels tight but I am going to check my static timing in the morning just to make sure that isn't the problem.

The only thing different I did before the cruise session was top off my tanks and add some lead substitute. I had also been running my port tank but switched shortly after topping off. I hope this additional info doesn't confuse the situation any.

Also, my tune up is very fresh with new plugs, wires, rotor button and cap. I run a Pertronics ignition and all seemed fine until after the long cruise at moderate to high speed day before yesterday.

Any ideas? Need more info that I didn't already note?

Thanks,
Bill

Re: Operating temp for Mercruiser 165 L6?

hi pb. glad ya made it back from yer vacation in one piece. hope ya caught a lot of fish too.

the 140-160* is right on for rwc. a t-stat will vary from those numbers when operating proper. 180* is a shade high. i river run 51 miles one way to my favorite marina. my temp gage stays in it's normal operating area. i run in the 2500-3500 range. sorry i'd give ya the numbers, but my temp gauge is either green or red, no numbers. mine is consistant though. only time mine goes above normal is after i stop after a hard run. after a restart temp will go avove normal if i wasn't stoped to long, but comes right back down real fast to normal again after the restart. the detonation would be real concerning for sure. think i'd start with confirming all my tune up numbers. timeing, dwell, pull the plugs and inspect them. maybe find one of them sparkplug reading guids on line somewhere or in a book. see if the plugs have any abnormality. reel poor had a spark plug reading thread going real recently too. might look at that. http://forums.iboats.com/showthread.php?t=202188&highlight=spark+plugs
ya might also think about doing a compression test just to be sure everything inside is ok and that nothing has changed. though to me. something is amiss since it was ok before, and has now devoloped a symptom.

don't know if the fuel tank thing means anything or not. was the fuel in the starboard tank fresh too? did the issue go away if ya switched over to the port tank? if not, i wouldn't think that'd be the issue.

when did ya last do yer impeller? for overheats. 1st thing i'd suspect would be the impeller.

Re: Operating temp for Mercruiser 165 L6?

Did some checking this morning. First I checked the timing which was dead on 6 degrees BTDC as it should be at 500 rpm. Funny thing it seems to have gone back to it's smooth as silk idle since I started it up this morning. Idle temp on muffs is still 140.

I have a couple or 3 thoughts on what may have happened.

1st, I may have fouled the chambers and plugs running the long cruise. (too rich) I will pull the plugs and check them as soon as some shade arrives this afternoon.

2nd, my distributor has a vacuum advance lever which is not currently tied down securely. I set the base timing with the lever at the full retard position and didn't think it would move on it's own. I could be wrong with that assumption however. ;-) Should there be a vac advance lever on my distributor? I am thinking no for a marine application.

3rd, I still haven't checked the mechanical advance. It could be sticking in a full advanced position causing the rougher idle when I throttled back down after the short WOT run. It may have returned to normal this morning when I cranked it up. My Blazer's 350 had that happen once and it burned the spark plug boots right off some of the plugs. Freed it up and it worked fine since.

My peak temp of 180 happened just after the WOT run but it soon came back to 160 and less when she was idling. I'm hoping it's an easily fixable timing glich and nothing more.

Any other thoughts you may have? I'm all ears.

Re: Operating temp for Mercruiser 165 L6?

Oh, haven't changed the impeller since I bought it last year but the previous owner changed it soon before I got the boat.

Re: Operating temp for Mercruiser 165 L6?

no vac. advance lever on either of the L6's i've had pb.....

once again, were in the same boat, reguarding our impellers. i'm runnin on an unknown one too. dealer alleged that it was R&Red for me prior to the sale... who knows. probably was as mine seems to work ok, but....i keep a real close eye on my temp gauge though as i only kinda trust dealers.....

Re: Operating temp for Mercruiser 165 L6?

I think now that distributor is an automotive one but will try wire tying the lever back just to make sure any unwanted timing changes can't happen. Thanks for your replies ziggy, you've helped me more than you know. I'll post a follow up on the other things I've yet to check. Dang it's hot outside today. LOL!

Re: Operating temp for Mercruiser 165 L6?

If you have to wire a lever back, something is broken.
If it is vacuum advance lever, something will blow up.

Re: Operating temp for Mercruiser 165 L6?

Care to be more clear on that, please?

Re: Operating temp for Mercruiser 165 L6?

Re: Operating temp for Mercruiser 165 L6?

"If you are running an auto dist., you are not Coast Guard compliant......
You need to replace it with a marine one.....
I'd look on ebay."

Yes Sir, I plan to asap. Just had a problem with the short answer before your's. Your reply is a good and helpful one.

Thanks much.

BTW importC, about that advance lever. There is no vacuum diaphram connected to it so it is not in use. My thoughts were that maybe since the lever was not secure it could have caused the possible over advanced condition I mentioned in my initial post. I know now 100% the lever should not be there following ziggy's helpful replies. I had thought it shouldn't be but was not certain until I asked. My desire to wire it securely out of action is a temporary fix and should not hurt anything until I get a proper replacement.

Re: Operating temp for Mercruiser 165 L6?

Well apparently I am running a Mercruiser distributor with a vacuum advance lever. See the pics for yourselves. I had assumed as a couple of us did that it was an automotive distributor but the label suggest otherwise. Looks like I will be wire tying up the lever anyway.

See the pics;

Re: Operating temp for Mercruiser 165 L6?

Never was a vac. advance system on a 6.
someone may have modified the marine base to accept an advance system from a car dist.or painted a car one black and installed a sticker

Re: Operating temp for Mercruiser 165 L6?

Yep, that ain't right.

Re: Operating temp for Mercruiser 165 L6?

yep, the short answer is, marine distibuters don't have vac. adv. .

i would be worried pb........

Re: Operating temp for Mercruiser 165 L6?

I agree it ain't right, probably a modified marine dist rather than a faked automtive IMHO. Either way I will fix it. I don't like it not being as it should be.

Thanks for the help fellas.

Re: Operating temp for Mercruiser 165 L6?

hope ya can find a ebay one or something bill. just went over to dougrussell and a complete new distributer is still available. $736.18....yikes............there's three part #'s, don't know which one ya need....price is all the same though......