overheating issue... i'm stumped

[garth155]

Hello, I have recently purchased a 2001 1900 sr with a mercury 5.0, it only has 90 hrs and as I'm finding out, they were hard hours full of neglect. The boat had sat in the desert sun for the last year and a half, baking the interior and paint. I have dealt with those issues and moved on to the mechanics of the boat. Until now I have only owned river jet boats and was very good at doing the proper maintenance. I did the basic engine tune up and started the motor (with water attached). The temp rose to about 200 degrees. Calling the local dealer he suggested replacing the thermostat and impeller (alpha 1). The thermostat looked original and was very badly rusted, the impeller wasn't all that bad. I completed both projects, fired the boat up and the temp again rose to around 200 degrees buzzer alarm and all. I am unfamiliar with the inboard/outboard set up and would greatly appreciate any help I could get. My wife and kids are turning on me as we sit out another beautiful weekend on the sidelines without a boat.

[mmwjr]

OKso new impeller. Pull the hose from the transom to the t-stat house to verify you are getting good water flow here, only run for a minute. Since you did the t-stat next place is to inspect the manifolds and elbows as these are water cooled and either become clogged to rust through. Get yourself a handheld IR thermal gun and take temps around the engine it should all be no more that 160 F which reminds me did you use a marine t-stat rated at 160 F? Also get a aftermarket mercruiser manual.

let us know what you find from here.

PS: welcome aboard

[CountryME]

Garth,
I have always been told to trust my instruments, but based on what you have done so far, you need to rule out the temp gage as reading correctly. The IR gun should help. Did you put a mercruiser thermostat in it, or a automotive one? The automotive t-stats are set to 190, the mercruiser ones are set to 160, as mmwjr said.

-JP

[pascavone]

simple, use your garden hose, for water flow, and pull the hoses, until your find what desert animal, or critter, build a home in the water passage.

Simplest solution is usually the best....

[mmwjr]

JP, Garth said his temp guage was reading 200 and the alarm went off. These are 2 seperate sensors so I assumed it's a real issue, however both sensors could be bad.

[jrsick]

I'm with Pas, your waterflow may be blocked. When you replaced the impeller, did the water tube look to be in good condition and fit properly on top of impeller housing? Other considerations: could the seawater pickup vents be obstructed? Is engine mounted water pump working? Is hot water exiting the engine?

[CountryME]

Thanks Mike, I missed the part where he said the buzzer went off.

[shrew]

Deleted Duplicate post and moved this post from 'Maintenance' to 'Engines' since it had active replies.

If impellor and thermostat didn't resolve the overheating issues, the next step is to look at the manifolds and risers. If the cooling passages are blocked with corrosion you will have overheating issues. If this is a cloosed cooling system, you should also crack open the heat exchanger and check for blockages.