Dman1991

Member
Mar 20, 2018
32
Boat Info
197i srv 260 twin 470 mercruiser Ann's mercruiser alpha 1 stern drives
Engines
Twin 470s with alpha 1 stern drives
Hey guys i have a 1978 srv 260 with twin 470s.. both engines run top knotch. My issue is with the cooling system one engine temperature gauge creeps up and up and up until i pull it back off plane. I can run them both at 2500 or less there fine as soon as it starts pushing water to plane it creeps up i can run on plane for about 3 min before it gets to 190 where i slow it down other engine runs 165 all day reguardless.. my question is how often is it that its an impeller issue in the outdrive?? I took off exhaust manifold and thermostat replaced, the manifold exchanger was clean of debris. Have not checked the 4 inch round heat exhanger but water flows good on the ear muffs when running out of water.. what do you guys think?
 
Lots of variables that can effect the life of an impeller. I would just replace them both for piece of mind since the boat is new to you. To answer your question, I expect to replace mine every second season and carry a spare. Upstream of your outdrive, you probably have an oil cooler, if you have power steering. It can trap pieces of impeller if there is material missing.
The heat exchanger is also easy to check/clean. Just remove the end caps. There should be a brass plug on it's inlet side that has an anode on it. I replace it every season but do run in salt water.
 
Well its not new to me this is my second year.. i rebuilt the impellers last year new gaskets and housings old impellers were started out of the water after sitting for a few years thanks to the previous owner smh!!! Needless to say there were pieces of the impeller i removed. Its done this ever since the first day i put it in the water.. we always cruise around at 1800 rpms or so 8 or 9 knotts so i don't really worry about it but would love to have the issue fixed so i could potentially run it on plane.
I am only asking for opinions on it being the impeller to see if its a waste of time and oil and everything to remove it from the water and all that work lol
 
There must still be a piece of impeller somewhere in the raw water loop . I would he digging into it more specifically the oil cooler and exchanger . Any molded hoses in either coolant or raw water loop as well. When I purchased my boat I replaced every hose on it as they were all 30 years old . They might look ok from the outside but close inspection of mine showed age damage and were prone to collapsing .
 
Well thats exactly what i was thinking starting with the coolers and hoses is there a way to kinda back flush the cooling system. And also if i remove the caps on the raw water heat exchanger tube do i just have to replace the end cap seal or are those reusable ?
 
I'm sure you have solved your problem by now but I had the same issue on my 77 240 Sundancer with twin 470's. My starboard engine would go up to 190 if run at 2500 and 3/4's up the gauge when on muffs where the port engine half up the gauge. They both had new impellers so I knew that wasn't the issue so I flushed both exchangers and hoses and boiled out them with meratic acid as there was a buildup of scale or something in them. I have a closed cooling system so flushed it out and it had some black crap in it and then replaced both thermastats and put new 50/50 antifreeze back in. That helped alot but when I checked the risers I noticed that they were running hot so I removed them and ended up replacing them with some good used ones from Ebay. I also noticed that the shutters in the exhaust pipe were missing so I put new shutters in to prevent the water from entering the engine when stopping the boat. Now when I run the engines on the muffs(haven't had a chance to get it back out to the lake) the temp at the gauges are only at the 1/4 mark and the risers are staying touchable. I am hoping to get the boat out as soon as it cools down here in Vegas.
 
Well honestly mines not fixed yet. I pulled the outdrive off new impeller housing and wear plate also impeller. Same results i did recently notice the engine that over heats is not putting exhaust out the propeller like the other side so i must have a bad exhaust bellows maybe my problem is in there somewhere
 
At this point im just limping it through the last final month of boating season then gonna trailer it to my house and dig into it over winter
 
Sounds like a plugged riser, if you are running in saltwater than your risers should be changed every couple of years especially if you don't flush your engine with fresh water after use. You should be pumping water out the prop with the exhaust if something is not plugged. There is a hose going from the heat exchanger to the riser and that supplies water to your exhaust from your outdrive pump see if there is water coming to your riser. Be quick it will be hot so only run your engine for a few seconds. If no water there then it may be a plugged hose or exchanger if plenty of water a plugged riser or the shutter may have broke loose and is plugging your exhaust. If you have your out drive off you can look into the exhaust bellows and see if the shutter is laying in there. Also if you have a closed cooling system check the thermostat and the condition of the antifreeze it cannot be higher than 54% or lower than 50% and be nice and clean. If it hasn't been changed for awhile then it should be. As for the risers new ones are hard to find and are expensive but I found some good ones on Ebay from people that run the Great lakes and only fresh water. Be careful running a broken motor could do more damage and these motors are hard to find that are in good shape.
 
Sounds like a plugged riser, if you are running in saltwater than your risers should be changed every couple of years especially if you don't flush your engine with fresh water after use. You should be pumping water out the prop with the exhaust if something is not plugged. There is a hose going from the heat exchanger to the riser and that supplies water to your exhaust from your outdrive pump see if there is water coming to your riser. Be quick it will be hot so only run your engine for a few seconds. If no water there then it may be a plugged hose or exchanger if plenty of water a plugged riser or the shutter may have broke loose and is plugging your exhaust. If you have your out drive off you can look into the exhaust bellows and see if the shutter is laying in there. Also if you have a closed cooling system check the thermostat and the condition of the antifreeze it cannot be higher than 54% or lower than 50% and be nice and clean. If it hasn't been changed for awhile then it should be. As for the risers new ones are hard to find and are expensive but I found some good ones on Ebay from people that run the Great lakes and only fresh water. Be careful running a broken motor could do more damage and these motors are hard to find that are in good shape.
G
I think your shutters have been dislodged and the pieces are blocking your exhaust.
 

Forum statistics

Threads
112,950
Messages
1,422,862
Members
60,932
Latest member
juliediane
Back
Top