high temp warning at high speeds (3200-4200 rpm)

S

Sea Ray Mike

New Member
Jul 1, 2008
37
South Carolina
Boat Info
Sundancer 260
Engines
Mercruiser 5.0L Bravo MPI----350 ci
I have a 2002 sundancer 260 5.0 bravo with 250 hours. Just put in new risers, manifolds, alternator, water pump. Took boat out and was running well then about 5 minutes into trip and moving at about 4000rpm warning signal goes off showing high temp!! I shut off engine and let it cool down. Then started up and cruised for 30 minutes at about 2500 rpm and boat ran great , no high temp. Then got closer to home base and ran it up to 3800 rpm and again heated up, lowered to 2800 rpm and it cooled down. Does anyone have suggestions as to why it would heat up at 4000 and not 2800?? Thanks so much.
Mike
 
Raw water pump? Whole pump or just impellor? Sounds like not enough flow. Got a thru hull or does all intake water go thru transom assembly.
If so could be a case of bravoitis. Likely with a boat of that age
 
Just had the same problem last week.... Ur not getting enough water pressure to cool the engine at high RPM. I changed both impellers and the problem was that one piece of the old impeller was blocking the hose that feed the engine and blocking the flow of water. Have ur mechanic take the water pump and check the water pressure on both sides. Should be an easy fix:)
 
sundancer350 said:
Just had the same problem last week.... Ur not getting enough water pressure to cool the engine at high RPM. I changed both impellers and the problem was that one piece of the old impeller was blocking the hose that feed the engine and blocking the flow of water. Have ur mechanic take the water pump and check the water pressure on both sides. Should be an easy fix:)
Click to expand...


Thanks so much, the mechanic did put new impellers in, but your saying is that the old impeller parts were blocking a full flow of water thru the system, correct?
Also, is there also a circulating pump on other side of engine? If so I have never changed it out , so the impellers in that pump may be bad, would that also cause the same problem?
Mike
 
Definitely try the circulation pump ( or in the auto world the water pump). Your problem is definitely caused by your rate of flow being far too low. Your temp increase at higher rpm's is a blessing in disguise. It's one of those few and far between yet noticeable warning signs a boat gives to let you know it's time change something before "KAAAAABOOOM"!
Also keep in mind that I say this because you have already done manifolds and risers. If you hadn't I would have said start there.
 
Greg, thanks.
Just want to make sure . I have a water pump on the left side of engine and a circulating pump on right side. Since I put in new water pump you are talking about the circulating pump,correct. So, by the 2 posts I got it seems I try the following.
1) Look to see if obstacles have blocked lines in water pump,
2) Check circulating pump

Thanks
Mike
 
scoflaw said:
Raw water pump? Whole pump or just impellor? Sounds like not enough flow. Got a thru hull or does all intake water go thru transom assembly.
If so could be a case of bravoitis. Likely with a boat of that age
Click to expand...

+1 need to check the tube through the transom assy. Look for this.
 
we have a fresh water flush out tube,which by passes the water inlet at the transom which you have showed corroded in your picture,we ran water thru the flush tube and the right side of the engine runs at about 125-130 degree and left side runs 175-180 degrees. does that show we do not have the corrosion in the inlet tube as shown in your picture.If so do you have any suggestions as to our next move to solve this overheating problem
 
that flush tube cap needs to be tight or the pump will start sucking air
 
Scoflaw, thanks for responding, and the answer is yes, the engine overheated before we put on new risers, manifolds etc. The picture you senT I showed my mechanic and his thinking was that if we by- passed that input intake shown in your picture and ran water through the flush tube(used to wash out the salt water her in Beaufort, SC) which by- passed the input intake in the transom and the right side still overheated, then that would eliminate what you showed in your photo as a problem. Would you agree. Now my mechanic thinks there is a blockage in the water jacket because he is running out of things to do.. He was going to take out frozen plug and see what he can do to flush out system. Do you have any suggestions?? We have done about everything except for the water jacket. He even pulled off foote and took apart. We now have the boat out of water. Thanks and help would be appreciated.

Thanks
 
Sea Ray Mike,

I might be late to the party here but if you have a FWC system, meaning a heat exchanger tank, the heat exchanger tank can cause this exact problem and can usually be fixed by taking it off and flushing it out with muriatic acid or a soak at a good radiator shop. Broken pieces from the raw water pump can wind up here too. I’ve had this exact problem on a FWC engine and that was the fix. More than likely you have a raw water cooled system on this boat but I didn’t see any mention of it. I just thought I would throw this out here.

AAK
 
With raw water cooled chunks can be in the PS cooler and the Tstat housing. Garden hose is not going to give you real world results.
If you get it back in the water you can do a water volume test, so many gallons at a certain rpm for a certain length of time.
 
I do not have a closed cooling system. Engine is cooled by the salt water that comes in through intake holes by foote. We have already cleaned and re-drilled the intake holes. Today we are taking off the right riser and manifold and see if we can get to freeze plug and check and flush out if water jacket is clogged. The hoses have all been checked and are clear.
 
As mentioned, impeller pieces in places like the PS cooler are a likely culprit. I doubt the problem is in the block. before I looked there, I would check all the coolers (PS, oil, and fuel), and the Tstat for blockage. These are the restrictive areas that tend to trap debris.
 
I would check intake hose. Remove drive and backflush to make sure you have good flow. Friends boat has similar issue. Lots of blockage. Good idea to split outdrives every other year and clean growth and anti foul inside so no crud grows. Especially if leaving in water.
 
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