Over heating

[wildemike]

I have a merc 4.3 MPI #OM407628 alpha gen 2. I am over heating going to 200 degrees, I replaced impeller, replaced thermostat, replaced serp belt and the spark plugs as well the starboard risor is getting hot ,port is cold, I'm thinking circulation pump replacement! I'd be very gratefull for any suggestions on this issue
PS: also ran salt away thru the system

 

[tazrig]

Re: Over heating

When you replaced the impeller was it intact? All splines on it intact? If not try to find where the missing pieces of rubber went. Take the thermostat out again and probe around with your finger or piece of wire to see if you can locate the piece that may now be blocking your water flow. Also risers should always be replaced in pairs. Have you checked your manifolds to see if they are blocked? Is your motor raw or fresh water cooled? When you start your engine grab the hose going from your circulating pump to the t-stat housing. Is it cold and feel full of water? If so it is working. How long does it take to overheat? Does it just go right up to 200 from idle or only at high speed and then go back down to normal when you slow down?

 

[wildemike]

Re: Over heating

at idle it slowly creeps up to 200 no alarms are sounding,impeller was in perfect shape , risers were replaced as a pair,raw water cooled, muffs were on tight.

 

[wildemike]

Re: Over heating

circulating pump is 10 years old as well

 

[wildemike]

Re: Over heating

circulating pump is 10 years old as well

 

[tazrig]

Re: Over heating

at idle it slowly creeps up to 200 no alarms are sounding,impeller was in perfect shape , risers were replaced as a pair,raw water cooled, muffs were on tight.

Do you have plenty of water pressure going to the muffs? You might want to try just putting your boat into the water (if you have a nearby ramp) doesn't even have to be off the trailer just so the sterndrive is well under water and run the motor to see if you have the same results before you go spend the money on a circulating pump. Many times it is just that there isn't enough pressure going into the drive. Circulating pumps when they go bad usually start to make a "ticking sound". The impeller in them is usually brass or aluminum and can easily last more than 10 years. If it is still overheating and you can't find a leak or blockage in the system then you could try replacing the circulating pump but based on what you've said I would save that for last.

 

[tazrig]

Re: Over heating

You might also want to get an IR gun and point it at the engine (at the temp sender) to confirm the actual temperature to rule out a bad sending unit and or gauge.

 

[wildemike]

Re: Over heating

I was having having this issue while out on the bay had to bump engine speed up for a few seconds till temp dropped back down then it would be ok for a bit more trolling. Thats what got me changing out stuff trying to zero in on the problem.

 

[tazrig]

Re: Over heating

OK so we know the same symptoms exist on the muffs and in the water. We know it isn't a blockage as it would either get worse with higher rpms or clear the blockage. Risers are good. Sounds like one of 3 things.

1) It isn't actually overheating. Bad gauge or sending unit. Confirm with IR heat gun

2) Drive impellor instal faulty. Re-check step by step here:

View attachment A1G2 Impeller Replace.pdf

3) Circulation pump

I would check #1 first to rule that out could just be a faulty wire, sending unit or gauge. Go over #2 to make sure in your head you didn't miss something and that the instal is tight and not squirting water out from where it shouldn't be (you might need to replace the whole water impeller kit not just the impeller) If it is that would account for raising the rpms temporarily fixing the issue by pumping more water into the motor to cool it. And lastly if all else checks out you may be right about #3 but if the circulation pump isn't Ticking than I'd try #'s 1 and 2 first.

 

[wildemike]

Re: Over heating

temp senor was also replaced dash board gauge is one with oil, temp, and rpm combo I;m starting to lean on the water pump as the culprit. Impeller was a kit replacement all was done properly ! this really bites!

 

[tazrig]

Re: Over heating

A recirculating pump at iBoats.com is about $85 give or take. You can confirm your part number here:

https://webapps.brunswick.com/literature/literatureSearch.do

It's up to you but I would check the motor with an IR gun before spending for a new pump. Many auto parts stores will rent you one for a couple bucks or even just loan you one for free. That would allow you to check not only the temp at the sender (to confirm overheat) but also at the starboard manifold as you know the risers are good. If you confirm the engine is overheating with the gun then replace the circulating pump based on everything else you've told me. If the starboard manifold is running way hotter than the port one (a little temp difference is ok) than you may need to replace it as well. As with risers, replace them in pairs. You might also try running a new wire from the sensor to the gauge just to rule that out a frayed wire. Just trying to save you some cash but we have eliminated a lot of stuff. If it's actually overheating then it's your circulating pump or your manifold or you just have so much crud inside your engine's water jacket that not enough water can circulate but let's assume for the moment it's not that.