98 mercruiser nagging OVERHEAT problem??

[MFD442]

hello all,

i have a 98 mercruiser 5.0 w/ alpha drive. i have been chasing an overheating problem for 2 seasons now. it will run at around 200 degrees at idle and 225 when at slow speeds. the temp gauge will dance eratically from time to time. once i try to start moving i will run upwards of 225+ and will get an overheat alarm. I have so far changed the impeller, water pump, risers, and mainfolds. my marina mechanic is running out of ideas as am i .

i am thinking that i can rule out a faulty gauge/reading b/c the temp gauge and alarm run off 2 different sensors so if they are both showing a problem, then there most likely really is one.

one thing i noticed is that the small hoses from the tstat housing to the risers feels kinda "crunchy" i am wondering if that is normal or could it be setiment or salt deposits restricting water flow?

there was a thread chronicling the same issue i have but he stpped posting after finding a snapped impeller shaft. my mechanic just did my impeller last season as a part of this problem so i can only assume that he would have noticed a shaft issue?

has anyone come across an issue like this?

thanks,

John Geldert
long island, NY

 

[kikroks]

Re: 98 mercruiser nagging OVERHEAT problem??

did you change your themastat

 

[MFD442]

Re: 98 mercruiser nagging OVERHEAT problem??

yes, t-stat , impeller, risers, and manifolds. what is weird is the violent swings on the temp gauge.

 

[chiefalen]

Re: 98 mercruiser nagging OVERHEAT problem??

When was the engine mounted water pump checked? I mean actually took off and the vanes examined?

You have power steering? If yes check that it ain't clogged.

Take off the hose running from the drive the long one to the t-stat and check that.

You can try running it without a t-stat see what happens.

Nothing clogging the t-stat housing?

How's the timing? Certain conditions when it's not right will make it run hot.

 

[MFD442]

Re: 98 mercruiser nagging OVERHEAT problem??

today i spent the day working on it. i changed the t stat again just to be safe. i then bypassed out the raw water supply from the impeller w/ a garden hose. it took some "rigging" but the setup was water tight. i diverted the raw water from the impeller out the side of the boat. it seems to have good fllow from the impeller. while running on fresh water from the hose, the engine still ran hot.

i also changed all the hoses from the t stat housing to both manifolds as well as to the water pump. the water that came out of the hoses did not seem overly rust filled or anything else that would raise a flag.

the water pump on the engine is only a year old, but i may try changing it again as a precaution.

i am hoping that it doesnt turn out to be a block issue.

from what i understand this system is fairly simple. water goes in the t stat housing and flows thru water pump, once at 160* the t stat opens and allows water to exit to the manifolds.

any ideas as to something i might be missing????

 

[littlebookworm]

Re: 98 mercruiser nagging OVERHEAT problem??

If I am understanding your posting correctly, you seem to have changed most of the hoses and seem to have eliminated the through-transom fitting as well as the hose from the outdrive to the transom. Is that correct? Is the flow from the transom fitting, through a hose which dumped overboard, steady and full? If not, i'd suggest you replace the fitting and/or the outside hose. They're known to collapse over time. I had the outer hose go bad on my previous boat. PS, make sure you get an original hose; the length is critical in preventing kinks. If all of that is OK, I would suggest you replace all the remaining hoses; one or more might be collapsing internally. I'd also suggest that as you're doing that, disconnect the power steering cooler and check it visually for blockage. Good luck. Hy

 

[MFD442]

Re: 98 mercruiser nagging OVERHEAT problem??

yes the water from the impeller was steady and constant as it flowed out the side.

i was leaning towards a supply problem, untill i bypassed the raw water intake from that area w the garden hose. when the enging overheated while running on fresh water supplied by garden hose i figure that i ruled out any and all hoses in and around the transom area. i would think that i have isolated the problem as being something past the t stat housing? unless i am missing something ?