454 overheating

We have two 454s dirct drive threw a Hurst transmission. The port engine when started and warms up will go to 180 then drop back to 140. I have replaced- raw water pumps (old ones looked good), -thermosatats (old ones looked good), -had the risers over hauled (they were a little cloged). Problem continues. Boat runs at 140 on gauge at 1400 to 2,200RPM. At 3,800 RPM both engines go to 180. Only thing I have not replaced is the engine glycol water pumps. The engine that goes to 180 has the hot water tank on it.
 
We have two 454s dirct drive threw a Hurst transmission
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If you are fresh water cooled, a cheap and easy solution may be the heat exchanger. At cruising speeds (3400RPM) my port engine would creep up to and sometimes over 180, while the starboard was stable at 165 all the time. I did all the stuff you just described to no avail. At the recommendation of a buddy (J Levine) I pulled the heat exchanger and took it to a local radiator shop that also services marine heat exchangers. After a boil out, pressure check, replacement of one bad tube and a re-spray, the two engines run steady as a rock at 165 all the time. Cost = $130. Not having to constantly watch and worry about the temp gauge: PRICELESS!
 
Well, I am stumped. I replaced the thermostat and checked the balls and the dang thing still overheats at low RPM's every now and then. She can go a couple days and works with no issues and then all of a sudden the temp just shots up. I have to put it in neutral and rev up the engine to bring the temp back to 145.

So, today I pulled the lower half of the OD to replace the impeller expecting to find a damaged impeller, but no, it looks like new. See attached photos

The only thing I see that is weird is that the impeller does not sit perfectly in the center. Since this is the first time I have ever done this before, I have no idea whether that is the way it is suppose to be or not. If it is not, I have no idea how to correct it since the hole in the top of the housing dictates this.

Anyone have an idea what I am missing here?
 

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I have not read the entire thread history but it sounds like you are picking up some trash maybe from time to time.

Not sure if you have raw water strainers but the symptons you describe are exactly what ours will do if the bottom of the strainer is clogged.
 
Wayne, back to post #7, you need manifolds and risers.
 
H2ONUT, I have less than 50 hours on a $7000 engine overhaul so I would have to assume that would not be the case. Just to educate myself, how would bad manifolds and risers cause my problem. Thanks for your help
 
Wayne
I'm way too lazy to go back and read all the previous stuff but could it be a bad sender? Are you absolutely certain the engine is running too hot (or is it TO hot ;-)? Have you shot some laser temp readings? Senders are readily available from MarineMax, pretty cheap and very easy to replace.
 
Stu said:
H2ONUT, I have less than 50 hours on a $7000 engine overhaul so I would have to assume that would not be the case. Just to educate myself, how would bad manifolds and risers cause my problem. Thanks for your help
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I thought the same, had a bad exhaust manifold, covered under warranty.
 
Stu said:
H2ONUT, I have less than 50 hours on a $7000 engine overhaul so I would have to assume that would not be the case. Just to educate myself, how would bad manifolds and risers cause my problem. Thanks for your help
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mrsrobinson said:
I thought the same, had a bad exhaust manifold, covered under warranty.
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A dockmate had changes his manifolds and risers just because they were 7 years old and wanted to be one step ahead. Well, genuine Mercruiser parts were installed by him. Ran the river for a weekend and had no issues. The next weekend he was 4 hours into a trip and had overheating issues. Got back to the dock and swapped back in the old manifolds and risers, boat ran great. Had the manifolds sent back to Mercruiser and found one of the manifolds was bad. Got a new one sent out, replaced everything again and no more problems.
 
I had an 87 Sundancer with the same engine and outdrive that had similar symptoms. The dealer put clear hoses on it to see where water flow problem was. Turned out that above 3500 rpm, the intake on the outdrive could not get enough water. The dealer could not troubleshoot this problem for months. Merc sent a service rep out and he installed small scoops over the water pickup that faced forward. Problem was solved.

Might be a longshot in your case, but thought I'd mention it just in case the more obvious answers are not solving your problem
 
Stu,

Did the $7000 overhaul include new manifolds and risers? Did you replace the impeller even though it looked OK? I have seen where the impeller spins on the hub and therefore your water flow will be reduced.

Doug
 
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Thanks all, here is some answers to some questions that were asked.
- I have not checked the eng temp with a laser temp gauge, I don't own one, I will have to take it to a shop for that
-The manifold and elbows were replaced during the overhaul so they could be bad per a post above
-badabing, your problem appears to have been at high rpm's while I am having problems at low rpm's
- the impeller was replaced during the overhaul and since I have it a part will put a new one in now.
- the key on the shaft is still in place and the impeller hub seems good so I don't believe she is spinning free

I am still unclear how a manifold or riser could cause this. Could someone educate me on this?
 
Wayne, Order one of these. It's a helluva lot cheaper than taking the boat in to a shop. And it'll come in handy in the future.

96451.gif


http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96451

Risers and manifolds have passageways that water passes through. If these passages are constricted, the cooling water doesn't flow as well and the engine runs hotter. YOu probably knew this already. As to why NEW ONES would be faulty, my only answer would be manufacturer's defect.
 
UPDATE! Like I said, I replaced the thermostat and no joy. Then last weekend I replaced the impeller even though it looked like new and this weekend she never ran above 150. Looks like for some reason the old impeller may have been bad
 
Stu said:
UPDATE! Like I said, I replaced the thermostat and no joy. Then last weekend I replaced the impeller even though it looked like new and this weekend she never ran above 150. Looks like for some reason the old impeller may have been bad
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An impeller that has "set" can have all it's fins and still not work... But then again, I know people that brag about having car tires for 100,000 miles and have the steel belts showing... in-laws...
 
If there was a "set" the thing would look like it was still compressed into the pump housing even though it's sitting on the benchtop. Curious Wayne, did it have a set?
 
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