Overheating above 1,500 RPMs on 270 SD??

D

dakst54

New Member
Mar 19, 2007
10
For about a month now, my 1998 270 Sundancer has been running way too hot above around 1,500 RPMs. My mechanic has flushed out the intakes and taken care of a couple other issues, but the problem persists. He isn't sure what it could be, and now wasn't to do an overhaul on the exhaust.

I can cruise around all day when I keep it at a no-wake speed without it overheating, but the second I try to step it up just a little bit, it starts running hot.

Any ideas on what that could be?

Thanks!
 
Well, with no info on your boat it's not easy to troubleshoot. Please give us some info on engine, outdrive etc...


Sounds like a bad impeller to me but who knows....
 
Have you replaced the t-stat? How about making a run without the t-stat installed.

If your mechanic is confused already, might be a good time to find a new one IMO.
 
Is your engine Raw Water cooled or Fresh Water cooled? When were the Risers and Manifolds changed out last? When was the Raw Water pump last serviced with a new Impeller? Is the Ignition Timing correct? Give us something to work with and we'll find the cause of your Grief. Al W.
 
Thanks very much guys. Bravo III outdrive, fresh water cooled, brand new impeller, I don't think the risers and manifolds have been changed in some time (bought it recently, and although it was very well taken care of, I suspect the previous owner didn't replace those), 454 Merc. 7.1 liter, 310 horsepower engine.

Thanks again!
 
Here is a good thought. It's a good time to change out the Risers/Manifolds, with the Ceramic Coated ones and stick with OEM. (Very worth while PM). Before you go to this extreme pull the end caps of the Heat Exchanger and make sure the inside is clean of internal corrosion. Do you have a Manual and which one do you have? I'd say do to the "above 1500 RPM", factor that the exhaust system is at fault. Al W.
 
Whoa..............let's get some terminologies straight here. "Fresh Water Cooled" generally means the engine is a closed cooling system with antifreeze. If that's the case then the risers and manifolds shouldn't have anything to do with overheating. Raw Water cooled means that you are using sea water to cool the engines.

A bit more clarifiacation please.
 
Dave S said:
Whoa..............let's get some terminologies straight here. "Fresh Water Cooled" generally means the engine is a closed cooling system with antifreeze. If that's the case then the risers and manifolds shouldn't have anything to do with overheating. Raw Water cooled means that you are using sea water to cool the engines.

A bit more clarifiacation please.
Click to expand...
I am not so sure about that.
 
It does have a closed cooling system with antifreeze, but from what I understand, even that requires raw water intake to cool some portions of the engine. To answer a previous question, it's a 1998.

Thanks!
 
I am having a similar problem with the same engine above 2500 rpms. I will run at 170 below 2500 with a 165 thermastat. If I cruise on plane at 3200 I will spike to 195. :huh: I have replaced the water pump, thermastat and the impella. I will do new riser's and mainfolds this winter.
 
Fresh water cooled systems have an engine cooler where Sea Water circulates to cool the hot water from the antifreeze circulating in the block itself. If that is clogged, then you won't get enough flow of sea water thru that to cool the antifreeze circulating in the engine.

I am not a mechanic and certainly not an expert but the engine cooler is one of the first things I would suspect. I think someone already mentioned that maybe you ought to get a different opinion from another marine mechanic. Based on what I am reading here, that may not be a bad idea.

There are also several good threads on the board about cooling problems ( such as ths one http://www.byowneryachts.com/forums/phpBB2/viewtopic.php?t=4203&highlight=[/url]) that you may want to look at using the search feature. Play Date has helped a lot of folks diagnose these types of problems as well (which you will see if you find those threads) and you may want to get his opinion on the best way to diagnose your problem.
 
Really. There just isn't enough information to work with.

What has been done on the engine so far?
 
Diagnosing a problem requires knowledge of what makes this thing work in the first place. To clarify how a "Closed Cooling System" works it is important to understand that Heat generated by your engine needs to be dissipated so that the Temp. remains constant at a cool level determined by the Thermostat opening and closing. Dissipating Heat is the job of the "Heat Exchanger" which does exactly what it's name implies. Engine water circulates through the Heat Exchanger and is cooled by colder Sea Water and then returns to the engine which in turn lets the engine run at proper Temp..
The Raw water pump moves Raw Water, (Sea Water), from the Pick Up and pushes it through the Heat Exchanger where it absorbs the Heat from the Engine Water and travels on to cool the Exhaust Manifolds and then out through the Risers. If the Risers or Manifolds are clogged the free movement of Raw Water is impeded and you Engine will overheat. Al W.
 
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