500 efi hp running higher than normal

[Bear442]

Ok, here is a funny one...

need help from the engine GODS>>>

engine started running hot, well above what it normally does...180-195---
goose the throtte and it will drop to 150 again, where it aways runs.

up on plane runs at 150-160..it will sometimes sstart heading up but than drops,,,.drop off plane/idle starts drifting back up to 190
goose throttle and it drops back to 150.

So,,,
I check the sea water pump, looked good, but still changed the impeller,
Than I check the thermostat, changed it any way with new one.

Let it idle, everything looks good..150 tempt.

Go out and it runs 150-160....than 30 mins later, it drifting back to 180, than back to 150 again??????????? hour later drifting back to 180 than back again, 30 mins later drfiting back to 180 again.

Never drift up to 180 during running, just at idle.

Before I start looking for obstructions or ???? anyone ever run into this???

I once did back in the early 2000 on a 454 boat I had and kept on trailer, it was a thru the hull hose barb the broke due to corrosion between the hull and plastic barb thru the transom, but I can believe this is the same.....

I do have sea strainer on the engine, could this be an issue. I did notice a thin crust over the grate when I last cleaned them. I have not check this strainer again, but I will.

any suggestions before I start pulling every hose and checking. What about the engine water pump, is that used? Could it be a bad...new therostat?

[MOBILEMERCMAN]

The water hose going thru the transom often gets pinched by corrosion. Some thing to check. The flow at idle is low and a small restriction gets amplified. Also check for a loose or bad hose before the see pump. A little air getting drawn in will do the same thing.. At speed the water is forced into sea pump.

[Bear442]

I do have flush out connections on the transom, I did not check those, could a loose cap do this? I hope it is this easy.

thanks

[MOBILEMERCMAN]

Usually air entering equates to no flow but, anything is possible. If flow is obstructed it will create more vacuum and possible draw air in.. The place where the hose connects to the transom is a plastic hose barb cover thingy.. It is held on by 2 1/4 in bolts. If you remove you will be able to see if hose is getting pinched.. It is common in salt water after a number of years.. You will need a new gasket. Its a pain to access and inspect but, it should be on your list.

[Bear442]

I have access to a bore scope, I thing when I start getting into this later this week, I will run from the sea pump back to the transom with the probe in the hose and see If I can pick a good picture up. I am running out of ideas....thanks....I was hoping I just got a bad thermostat, but not likely....

[Bear442]

you know the more I think about it, it was the opposite, the barb issue created high temp off idle....huh...i need to start looing..

[MOBILEMERCMAN]

If you can not figure it out with your scope pull #20 and look in the end of the hose.

http://www.mercruiserparts.com/Show_pictures3.asp?dnbr=809808%2096&ivar=IMAGES/COMMON/18718.png&inbr=1943&bnbr=160&bdesc=GIMBAL+HOUSING

[Bear442]

thanks for the illustration, I will know Thurs evening. Thanks....

Sounds like you seen this, been there before.....

[BDARCHER]

Bear My BT is doing the same thing. Plus my water pump fuel pump bearing housing is leaking again. I got to change the bearings and seals again for the 3rd time. This merc part sucks.

[Bear442]

JIM:
I ran the scope thru all the hoses and engine cavities. There was bits of impeller in the oil cooler, not clogged, but there was some obstruction, floater, not small enought to go thru the cooler holes. maybe 20%. Removed all those, then ran up to the transom connection, # 20. It was ok and not an issue. I was using a high dollars scope ($30,000) you could see ever thing and it was in color. So bottom line is, that is all I found.

Ran engine for 20 mins, thru flush out connection, never got about 130. So I won't know until next run out. Although it never ran hot, I still can't have this behavior.

thanks

[MOBILEMERCMAN]

You should put it in the water and see what it does. You really can not troubleshoot heat issues on a hose. I am glad it is clear at #20.. That is a pita to service. It may be a good idea to back flush the cooler or visually check to make sure all the tubes are clear.

Talk nice to her and take a ride.

On a long shot verify the sender lead for the gauge is not loose or chaffed on the engine.

[Bear442]

been trying to go out, but the weather sinks

[Bear442]

ran yesterday, back to normal. Just a couple of pieces from the past bad rubber impeller that was never cleaned out of the cooler. Thanks for all.....

[35 Lightning]

I would check the strainer for blockage first.