4.3 running hot on one side

[alldodge]

Ever have the impeller come apart?
Yes, at least pull the exhaust hoses off and have a look inside

 

[13crazyhorse]

alldodge, I changed the impeller a couple of weeks ago and the vanes were all intact. At this time I changed everything housing and all cause the housing had a couple of score marks in it. Very pricey cause this is Gen 2 stainless steel housing. Exhaust manifolds and risers are very clean. Im thinking maybe like you stated earlier possible small air leak and the water supply although good is not quite enough to supply both sides. Taking the lower off now to double check the seals gaskets and o rings.

 

[Rick Stephens]

You can read Mercruiser's bulletin here on how to test water output on your sterndrive pump. Worth the read.

 

[Pzilly]

You probably have rust build up in the cooling passageway on that side, the block port is like a trapizoid, but the head gasket is a smaller round opening so once it builds up it can't escape, this very problem just cost me a 4.3, mostly because last years RV antifreeze couldn't get there, mine never over heated, but one side was considerably hotter then the other, after pulling the heads I found two blocked passages and between them a cylinder with a crack.

keep in mind my cylinde had 135 compression and passed a leak down test, boat only got water in oil under hard use, I would bet hard money your ports are blocked as our engines are same age, definitely fix this before winterizing.

as for solutions, once I pulled my heads I used a vacuum and then a small,pick up magnet down in the port, I then stopped when I saw the crack. A tech told me they use works toilet bowl cleaner to eat this rust, but not sure how you can would get it in there w heads on unless you made a solution that you pump in like winterizing with the bucket and pump method. I didn't pursue this once I found the crack but you should research how to clean the blocks cooling passages before you end up with my situation.

your boat is overheating, on that side anyway, you may not may not get an alarm as the overall water temp going past the sensor may not be as hot as what's going on in that specific section of the motor.

I could be wrong, but like I said I'd bet money I'm not as I just went through this same thing, hopefully you are catching yours before you get a small crack like mine.

 

[Lowlysubaruguy]

When was the last time you pulled each lower drain plug for the block. Put your water flushing muffs on it and have water running pull the lowest plug first on the side that gets hot does water shoot out of it at a decent flow. If not take a screwdriver and see if just the area at the plug is plugged up. Then check the other side either side could be the creator Ive seen blocks filled with sand mud what have you so bad that they cannot flow water and then they wont drain and freeze up and crack the block in the winter.

 

[13crazyhorse]

Well I pull the outdrive apart and took the impeller assembly apart to see if I did that correctly and everything was good. Put it all back together put it in the lake and the result is the same. It doesn't overheat but runs at 185 which I feel is too hot. One side or the other (manifold/riser) runs much hotter than the other which doesn't seem right to me. Maybe over the winter I'll change the circulating pump?

 

[alldodge]

185 is to hot for open cool,
You sure your IR temp gun is accurate?
At 185 the thermostat will be to hot to touch for more then a split second

 

[Lou C]

Did you do mercs test for the raw water output for the impeller?
if it puts out enough water and the exhaust is not restricted on one side; the only things I can think of are a problem in the t stat housing or an internal obstruction in the manifold. I’d also try disconnecting both manifold water feed hoses and hook up a garden hose to each one, then turn on the water and observe flow out the exhaust housing on the transom mount.

 

[13crazyhorse]

I did not do the raw water timed test but disconnected every hose watched the water flow, back flushed everything, taken the manifolds and risers off, taken the thermostat housing off twice there are NO obstructions anywhere. Everything is very clean and the water flow is fine. Temp gauge runs at 185 not the thermostat housing. One manifold will run at 120 ish and the other will run at 190 ish. After connecting and disconnecting the hoses doing different test while running the heat issue switched from one side to the other. THATS confusing.

 

[alldodge]

Temp gauge runs at 185 not the thermostat housing.

In this case I think you have a bad gauge or sender. The sender is in the thermostat housing, and didn't you verify the temp reading with the IR temp gun?

 

[13crazyhorse]

Maybe I presented this wrong. The temp gauge reads 185. I checked the thermostat housing (IR) and its reading 185-190. The problem is you cant hold your hand on the one side manifold or riser and the other side is only warm. At times this has changed from one side to the other side. I just am referring to the temp gauge because I think in the past it ran around 170.

 

[Rick Stephens]

Give a 140ƒ thermostat a try.

 

[alldodge]

Putting your hand on a exhaust elbow and not being able to keep your hand on one can be as little as 10 degrees. One side will always be hotter then the other, so I' not to concerned. Not the 185-190 Thermostat I am, even with a 160 stat.

The issue is the drive pump will move water thru the thermostat. The top of the housing should actually be cooler then the lower half. Raw water comes in and what does not go into the motor, exits the exhaust hoses. The lower section of the housing would have warmer water because its behind the thermostat

 

[13crazyhorse]

Its not an issue of 10 degrees difference its 60-70 degrees. I'm sorry but I'm not understanding your point on the thermostat. Before it opens all the impeller water should run into both exhaust manifolds? Could it be the circulating pump is not operating properly after the thermostat opens? It can fine for years with the correct (160) thermostat which was also recommended by the dealer.

 

[alldodge]

My point is the difference with keeping your hand on an exhaust elbow at 140 to 160 is the difference in keeping your hand on the elbow and not being able to.

You mentioned on exhaust elbow was 190, and that would be real close to melting the rubber in the boot

Back the the thermostat housing, raw water flows thru the top of the housing, so it should remain cooler then the lower.

I'm wondering if your IR temp gun is the problem

 

[13crazyhorse]

I misspoke if I said the elbow was 190 I meant the manifold. The IR temp gun is brand new from Lowes but only a cheap $30 model could be a POS. Maybe I'm chasing my tail for no reason here. Just don't wanna damage my engine if I can help it. Motor runs on after you shut it off and the dealer said that was cause it was running too hot. But it always did that so could be unrelated. Ive also read the 4.3 is prone to this. If you let it idle for a couple of minutes it shuts off ok. Motor doesn't overheat anymore so the alarm goes off which I think was around 210. Summer is almost over so I wont be fishing too much longer. Thank you everyone for your input I appreciate it.

 

[alldodge]

Run on (dieseling) can be caused by to hot, but also, incorrect timing, running rich, idle to high. Running for a bit prior to turning off is helpful for all the previous.

If you have a meat thermometer, get a pan of water on the stove and start heating it up and compare to the IR as it heats up

 

[Rick Stephens]

Dieseling can be a real motor killer if the motor reverses at all, which happens a lot. If it does, eventually you'll suck some water and potentially hydrolock. I don't really care what a dealer says when you have issues with temperature, do something.... like switch to a 140ƒ thermostat maybe? And fix the dieseling. My 4.3 has never ever dieseled, but I also spent the time to calibrate the carburetor to run without any lean spots in the various throttle settings.

 

[13crazyhorse]

Rick, I do understand what you're saying but I don't understand why there was no issue with the correct thermostat (160) for years. Obviously something has changed that should be corrected not compensated for. I am retired and living on SS so its not an option for me to keep replacing parts. As you know these damn boat parts are a little pricy! Thanks again.

 

[13crazyhorse]

Rick,
I must apologize, I decided to try a 140 thermostat just for the hell of it changed it today. I didn't take the boat out of the marina but for the initial test the gauge ran at about 170 instead of 185. I'm happy with this but don't know why the motor calls for a 160 if this works thats the bottom line I guess. One manifold still runs much hotter than the other but maybe I should accept that as the norm. I have yet to take it out and run it to see if the dieseling is still there.