Runs hot at idlle

skiierjeff

skiierjeff

New Member
Nov 18, 2010
25
Massachusetts
Boat Info
SRV240 Weekender 1977
Engines
260 Mercruiser
Hi:
I'm working to get my recently purchased 1977 Mercruiser ready for next season. I've never launched it.

Engine is original raw water cooled MCM 260. It spent most of its ife in fresh water.

I just replaced the manifolds (date marked 1982), riser elbows and thermostat. All new gaskets. No signs of any leaks. The stern drive is off, so I stuck a hose directly into the water inlet in the bell housing for testing.

At fast idle (1000-1200 RPM) the temp guage steadily rises to just below the red line. The manifolds and risers are both too hot to keep my hand on them. I can't feel coolant running through the rubber hoses (should I?). Some hoses are pretty hot, others coming out of the t-stat cover are only slightly warm.

It looks like lots of water exits the transom.

Do you think I have a problem or will it run cooler once its running for real out on the water?

Thanks if you can help.

Jeff​
 
Isn't the raw water pump in the drive itself (assuming it is pre-Bravo drives)? If it IS in the drive which is not attached to the boat, the water will not be forced into the engine. That would definately cause overheating.
 
Impeller replacement is the first step in cooling issues. If you have little or low flow from the drive to the housing, then the impeller is bad. If you burned up an impeller, you will need to take off every hose and find the busted pieces.
 
skiierjeff said:
The stern drive is off, so I stuck a hose directly into the water inlet in the bell housing for testing.

Jeff​
Click to expand...

Like he said - the stern drive is OFF. If the impeller is in the drive that's on the garage floor, that just might be the problem.
 
Can you post a picture of the t-stat housing area of your engine?

Are you sure the stat is in correctly? Might want to test it in a pot of water, noting the temp that it opens at, just to be sure it's functioning correctly.

How does the circ pump look?
 
Last edited:
Thank you to everyone who is making suggestions.

I'll try and get a picture of of the T-state housing next weekend.
The stat is definitely in correctly.
I do plan on testing the t-stat in hot water. I took a chance that being brand new that it would function. Maybe I lost that gamble.

Circ pump looks good on the exterior and shows no signs of leaking. I may pull it off next week if I have time.

I also wanted to re-emphasize to everyone who is trying to help: The stern drive if off, so the raw water impeller is not part of the system right now. I am injecting water from the garden hose almost directly to the engine. I think this test setup is providing more than enough pressure and volume. Lots of water is coming out the exhaust.


Please keep the comments coming. This is all very helpful and appreciated.

Jeff
 
The thermostat has no bearing on water flow into and therefore the temperatures of the manifolds and risers. If they are hot then there is not enough water flow. Did you fit the correct gaskets between manifolds and risers/elbows? If the wrong gaskets are used it will restrict the flow from manifold into the riser/elbow and cause everything to get too hot.
 
Last edited:
If you can't get a picture of the housing... do you have the "T" set-up on top of the housing where there are two extra hoses with a spring and ball set-up inside?
 
Once you're sure of the waterflow issues, check the timing. Too much advance will get the manifolds warmed up in no time.
 
"checkballs", you simply tighten the little lock nut(s) all the way down, untilthere's no more threads..........in other words, you bottom-out the nuts.There's no "setting" or "calibration" for theballs.....they're only to provide a slight back pressure to the "extra"flow from the drive, so the cool water doesn't simply go right out to theelbows without circulating through the block and keeping the system topped-off.Issues with the check balls usually cause overheating at low rpm's. Take off sand down clean and turn balls over on a fresh side. I dealt with this issue all last summer after replacing Impellers water pumps circulation pumps thermostats and T housings. Lets me Know whatcha find out....



Jon
 
Thanks for even more great tips. The problem appears to be solved.
I didn't get the picture of the T-stat housing but it soen's have a "T" set up. I looked up a picture on line of that type.

I removed the Tstat. It was installed correctly.
I proceeded to remove the Tstat housing. there are no balls in it.
I also started checking flow by working my way through each pathway of water from entry to exit through every hose, manifold, riser, water pump, tstat housing, and tstat cover.
Everything flowed very well. I also flushed out the engine block with water.
I turned the water pump on the engine manually and it pumped water
I then cleaned all hoses and fittings.

After putting it all together I ran it for a good 30 minutes. the temp guage never exceeded halfway. i took a cheapo infrared thermometer and checksed temps all over the engine and hoses.

Highest reading was on the aft end of the port manifold at about 210 degrees. Stb was about 185. Sound ok?

Fwd end of manis were much cooler.

anyway that's it for this year. i drained everything and added antifreeze for the winter. Looking forward to Spring launch and a real on the water test run.

Thanks again everybody. Its good to have friends with all of this experience. I hope when I learn more, I can help others like you helped me.

Jeff
 
Skiier Jeff,
Just wanted to jump in here; there are many more that have a ton more experience than me. 185/210 seems high. I had overheating AND pre-detonation issues (rebuilding my engine now) and the highest I could get after a new impeller was 127/134. I ran my engine to death after that and didn't have a problem - until I blew a piston. You should be able to sit there and have your hand on the exhaust manifolds all day long, but I suspect at those temps you won't be able to.

I was (and still am) concerend about my risers being clogged, and that could be an issue you're having too. I blew an exhaust riser hose at the beginning of the season, and when I pilled the risers, a TON of scale and crap came out of the little ports where they sit on the manifolds. Cleaned 'em, but not sure how sucessful I was. Have to assume that with temps as low as what I got, that they're ok.

I'll know more after the rebuild is done and I fire it up. Wouldn't mess around too long with temps that high though.
 
Thanks for the follow-up info. I definitely can't keep my hand on the manifolds. I will start checking into the pre-detonations thing in the spring. That sounds like a good lead. Thanks.

In case you missed my original posting, the risers and manifolds are new this month. They have zero hours.

Jeff
 
Sounds like the same problem I had took me 2 years to discover a flapper had fallen down into the. "Y" pipe

Ken
 
Missed the new riser thing Jeff... My engine's out, and I will definately check the exhaust shutter to be safe. The cost of a gasket for that is cheap insurance. Got word yesterday that my port head is cracked, right by the valve guide. Ugh. New heads on the way.
 
Rick K said:
Missed the new riser thing Jeff... My engine's out, and I will definately check the exhaust shutter to be safe. The cost of a gasket for that is cheap insurance. Got word yesterday that my port head is cracked, right by the valve guide. Ugh. New heads on the way.
Click to expand...

Might be a good idea to try to find out why the head cracked. They usually crack because of overheating.
If the engine is out you might want to look around a little bit at longblocks. By the time you buy a set of rebuilt heads and the gaskets you might be about halfway to the price of a remanufactured longblock.
I did the heads on one of my motors last year and the motor went bad on me this year.
I decided to replace the motor, then I decided if I was doing one I might as well do both. Since I really love the boat and plan to keep it for a while I went with two brand new Mercruiser replacements and half system FWC kits.
It's a big investment. But It will probably give me a decent run of trouble free service.
 
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Hi Ken,
That's a scary thought. I think my shutters are not servicible unless the engine is pulled. Yikes!

I guess I'll start figuring out if I can diagnose if that is the problem. I don't have any clicking noises. Other than that I don't know what to look for yet.

Anyway, this old boat is sure forcing me to learn a lot of new skills but it's a good vice to have I guess.

Jeff
 
JVM225, that's exactly what happened. I have a few posts floating around on it, but long story short, blew a riser hose in the beginning of the season. Replaced both of those. Ran warm/hot once, hauled out, changed impeller. Ran cooler but not all that great. I don't think the blown riser hose had anything to do with the engine failure however.

Changed thermostat, temp gauge, and ran boat until the end of the season, when I dropped the #6 piston. Pulled engine, piston butched, but neglidgeble damage to the cylinder itself. Tore down, sent to machine shop, they tested everything, found port head was cracked between the valves on cly #2.

Also found timing chain had 50 feet of slop in it. Shop said otherwise, engine was in awesome condition for being an '81 and machined everything up. New pistons, and all that machine shop stuff. Engine is about half reassembled now.

Freind's shop, I pay for parts and minimal labor. Have master mechanic helping with reassembly.

After all this, I want to make 100% sure the shutter is functioning the way it should be.
 
skiierjeff said:
Hi Ken,
That's a scary thought. I think my shutters are not servicible unless the engine is pulled. Yikes!

I guess I'll start figuring out if I can diagnose if that is the problem. I don't have any clicking noises. Other than that I don't know what to look for yet.

Anyway, this old boat is sure forcing me to learn a lot of new skills but it's a good vice to have I guess.

Jeff
Click to expand...

Jeff the flappers are at the top of the "Y" pipe one on each side, that is why you can have one side of the engine hotter than the other if one fails. The engine does not need to come out you just need to remove the bellows from the "Y" pipe and the flapper is right there. A nice 20 minute job.

Ken
 
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