Overheating 671N Need help!!!

[micky]

Overheating 671N Need help!!! UPDATE UPDATE

At idle the "hot" engine gets to 165 fast compared with the "cool" engine. At 1100 rpm the "cool" engine is at 165-170 and the "hot" engine is at 185. If I pass 1100 rpm the "hot" engine's temp. keeps going up. Both impellers are new, coolant is OK, thermostats are new. Temp checked with IR thermometer and the gauges are mechanical so I'm certain about the temps.

Things that I'm thinking that can cause the problem, the exhaust elbow may be blocked because of the years, or the coolant pump may be bad? I'm thinking about the coolant pump because at idle the engine gets to 165 a lot faster than the other one.

I'm open to suggestions for things to check.

 

[Jaxfishgyd]

Clogged heat exchanger was my problem a few years ago on one main and again with my generator a year later....

 

[micky]

Heat exchanger was also cleaned about 6 months ago.

 

[lisaann]

water flow out the back?

 

[micky]

Its less than the "cool" engine but I know that the "cool" engine has a broken baffle on the muffler. Also the "hot" engine sounds like it needs more water, the exhaust sounds drier than the "cool" engine.

 

[boatwright]

was the impellor replaced? did you get all the pieces or you might have blocked passages

 

[jim rosenthal]

Unless all the hoses in the water flow paths have been verified to be in good shape, I'd look at them. Speaking from recent experience, they can look fine on the outside and on the inside be delaminated and collapsing, especially under the suction of the engine trying to get sea water in to cool the heat exchanger. If they are old, they are suspect.

 

[dsharp]

If the impeller is good and you're sure the heat exchanger is clean the next logical suspect is the riser. Have you checked the temperature of the riser while the engine is running? You ought to be able to keep the palm of your hand on it while its running. i know that sounds dumb but it works. There's not much to go wrong with the circulating pump. Check the raw water pump for a worn out cam or end plate but that's kind of a long shot. As a previous poster was asking did the old impeller come apart? Once the water gets past the heat exchanger there are not too many places for a restriction than the riser or a collapsed hose.

 

[micky]

So I went to the boat and checked the hoses and found that the intake hose from the seacock to the water pump has no wire and is super soft. It has a small kink where it makes a turn on the back of the engine towards the pump. I'm buying a new one with wire today. I know this (soft wall hose) will affect me on high rpm's but will this be the cause on why at idle it goes to 165 a lot faster than the other engine??

The old impeller was complete, it had 8 vanes instead of 10 so I changed it out.

 

[bobk]

Thermostat?

 

[micky]

New and the old one had 1 year, I changed it just to be sure.

 

[dsharp]

If the hose is getting sucked shut it's entirely possible to cause the engine to reach 165 quicker. Even at idle the raw water pump is trying to move a substantial flow of water. I'm kind of surprised that it's getting that warm at idle with the gears in neutral. I ran a boat with the inclined version of those engines and you would have to put it in gear and let it pull on the ropes to warm up. Hopefully you found the problem.

 

[OBXTucker]

I'm with Jim on this one. It's either got to be the hose or a piece of impeller vane wasn't removed wih the last change. Did you replace the impeller or did a mechanic? Reason I ask is that I chewed one up earlier this spring. Mechanic helped with the changeover and he was meticulous in counting pieces/parts from the old impeller. Used needle nosed pliers to get the last few pieces out and put it back like a puzzle to be sure it all fit back together and nothing was left behind.

 

[Genevatexan]

Re-check Heat Exchanger? Like earlier poster, my overheat occurred above a specific RPM and was a clogged heat exchanger as well.

 

[Timeout]

My 671's have the fuel cooler about 12" downstream of the raw water pump. Easy to remove hose. This cooler has 1/4" holes so all pieces get stopped there. I check that every time I change an impeller.

 

[micky]

The old impeller was complete when I changed it, Fuel cooler is clean and heat exchanger is also clean. I changed the impeller myself. I'm going to replace the intake hose on sunday and give it a run and see. I'll report back.

 

[JLR]

Sorry to state the obvious but in reading through the thread, I do not see any reference to the possibility of a clogged strainer. First place to check.

 

[micky]

I have external strainers and they are clean. I checked them this past weekend.

 

[micky]

So I went to the boat today and replaced the intake hose with a new one with wire, checked the impeller and OK, checked the coolant pump and its ok. Talked to a neighbor that has the same engines and he told me that he had the same problem with one engine and that it was the exhaust riser clogged and that he cleaned it with muriatic acid. So did the same thing and the engine is quieter and I see more water coming off the exhaust. Next weekend I'll give it a sea trial to see if that was the problem.

 

[micky]

Still overheating. I took the exhaust elbow out and 3 of the 4 water passages were completely closed and the other one was 1/4 closed. I was able to open them up and installed it back and now it still overheats but slower.

Now at 1200 rpm temp is at 180 degrees while the other engine was at 170. I bumped the rpm to 1400 rpm and the temp started increasing temp to 195 and I slowed down. Here's the weird thing. I slowed down to 1200 and the temp was still at 195 and it took a while for the temp to start go down. I got to the marina and shut off the engines and 30 min laters the temp was still at 160. I'm leaning towards the coolant side of the cooling system but don't know where else to look.

The other engine is at 170-175 at all rpm.

I need suggestions.