running hot

[mrxitmt]

Today I took my 2nd run of this summer I had noticed the temp fluctuating between 175 then back to 150 when i pulled back on to the lift and shut the engine down I opened the hatch and could hear the water boiling in the circultor pump .I turned the key to on and the temp was around 200... What do you think..Thermostat or impeller in the lower unit ..Something else?This is very disapointing cause I just got the boat last year and it has a jasper reman 350.

[CountryME]

My first question would be when was the impeller last replaced? If you have an alpha one gen 2 and it has been more than 3 years, I would give that a try first. It's easy and cheaper than a water pump.

[jrsick]

I think you and country have it right; water pump impeller or thermostat. Thermostat check is easiest, but you will need a new gasket. Replacing the seawater impeller will also require you to change the outdrive lube. It is a longer process but necessary if your impeller is 2 years or older.

[biggerseagar]

I'll second that. Your engine should run around the 175 mark. Is the temp alarm hooked up on your engine? Any higher than 175 it should go off. But yes check your impellar first-then your thermostat. Then after that who knows?

Roger

[mrxitmt]

Thanks all.I will check these items friday . I don't know when the impeller was done ( I assumed that places that sell boats Checked these things)You know what happens when we assume.

[CountryME]

Don't check your impeller, replace it! For the Alphas, an impeller can look OK, but have hardened and will not provide enough flow. As an impeller replacement is about a $150-200 job for a dealer to do, they typically do not want to spend the money to replace it since it cuts into profit margin on a used boat. Let us know how you make out.

-JP

[mmwjr]

since the temp did not exceed 175 whent he engine is running you are not overheating, however since you don't know when the impleer was last replaced I would replace it. Regarding the rise in temp when you shut the engine down this is normal, while the engine is not generating new waste heat it has a lot of thermal mass that will retain heat for some time. The rise comes from the fact that you are no longer cooling when the engine is shut off. The temp will rise up for a short period of time (minutes) and then start to decrease as the wate heat dissipates by radiating into the air around it. The warmer the air in the ngine compartment the long it takes for this to happen.

I don't trust the accuracy of most gagues just use them as a reference. I would get an infrared handhelp thermal sensor and measure temps around the engine. This will tell you if the exhaust, engine, ... have hot spots and give you time to fix an issue before melting the whole thing down.

[ss3964spd]

I agree with Mike.

I will add, though, that the temp shouldn't really be fluctuating very much while the engine is running and up to operating temp. If the temp is swinging between 150 and 175 it may suggest there's an issue - likely the t-stat is hanging open.

[shrew]

I'm hesitant to pipe in here. The Temp. alarm should be going of at around 200. Water boils at 212. The engine should be running at 175. Bouncing is not normal. Bouncing between 150 - 170 is odd. I had this happen in an vehicle a few years ago and it turned out I had an air bubble in the closed cooling system. This does sound like a thermostat issue. Once you shut the engine down, i would expect the temps to rise. The engine is still 175 plus degress only now there is no longer any coolant running through it. Expect the engine to rise for a few minutes, then drop after you shut it off. Most people don't turn the key back to aux within a few min. of shutting down so they don't notice.

[jrsick]

All great comments and good advice. You mention temp fluctuations in your original post. I recommend that you check both the seawater impeller and thermostat. Check seawater impeller for a good seal at the top of the housing, it could be sucking exhaust gas. Check the thermostat for blockage/debris in the system. If something large has entered your cooling system it would be blocked by the thermostat. Both of these situations could result in temp fluctuations.

[ss3964spd]

Given that the engine is not over heating I don't think you have a water flow/volumn issue. If the impellor or the circulation pump were iffy, or if there was blockage in the system, I would expect you'd see the engine running hotter than 175-ish, especially at cruise speeds, as the first symptom. The particular symptom you described; fluctuating between 150 and 175, suggest to me a lazy t-stat. Keep a close eye on it to see if you can detect a pattern - like under what circumstances does it run at 175 and under what circumstances does it run at 150, etc-etc.

Still though, if you don't know when the impellor was last replaced it would be sound judgement to do so as soon as possible. They are made of rubber. As rubber ages it becomes brittle. When they become too brittle they break. When they break the engine over heats. When the engine over heats bad things happen. When bad things happen you have to throw a lot more money at it. Don't throw a lot more money at it if you can avoid doing so.

[biggerseagar]

I'll knock on wood here......but Jasper engines were famous for bearing failure years ago.............hope not!!!

Roger

[mmwjr]

Roger,
I hope you comments of "knock on wood" and "bearing failure" is not an attempt at a bad knock knock joke at mrxitmt's expense

Ok so beside replacing the impellor you may want to replace the t-stat. Removing a t-stat to test it in hot water to check it's function is a waist of time when the cost of a new one is low, then you are done.