Overheating Problem

[RobaloGator]

You guys were such help on my VelvetDrive fluid change, I thought I'd try again. As indicated before, I've put  a 1991 American Skier back in the water after 12 years. It runs great with one exception. It gets really hot while idling for just a few minutes. During the 22-24 mph wakeboard pulls, it stays right around 150F. When pulling a skier at 34-36 mph, it drops to about 130F. When idling between pulls or waiting to load on the trailer, it shoots up to 240F. Ouch! This has to be damaging to the engine. It seems that when moving, the water flow is good to great. What creates the water flow (or in my case, lack of) when sitting still? Could this be a water pump or thermostat issue? Any help would be appreciated. 

[skibug]

Thermostat is going bad, you have an impeller that is deteriorating, or the main water pump is going bad.  When you are underway the water is forced through the pick up under the boat and into your engine via the impeller pump.  When idling, the engine relys on the impeller pump to feed the engine; but, if it is loosing its rubber vains, it can't pickup and force water into the system.

[RobaloGator]

SKIBUG, Thanks for your comments. The boat is an inboard with an Indmar Model 250. I'm only awre of the water pump mounted to the front of the crankshaft. I can remove the cover to inspect the impeller to determine it's condition. Is there an additional water pump of any type on the motor? Thanks again.

[skibug]

The main water pump should be on the right hand side of the engine as you look at the engine facing the back of the boat.  Follow the hose that comes off of your impeller housing.  I think that hose feeds directly into the main water pump.  The engine belt will be looping around a pulley attached to the front of the main pump.

[RichardDoane]

Indmar usually has a crank mounted raw water pump.  Take the front cover off with the 4 little screws, and remove the impellor by spraying soapy water in the housing and then carefully prying the impellor out of the bore with a couple of screwdrivers..  If the impellor checks out ok, then check for a restriction for waterflow through the transmission cooler.  Disconect the hoses and make sure that impellor debris, weeds, or other stuff isn't restricting the water flow.  If the engine runs cooler at speed and heats up at idle then your problem is lack of flow at idle.

[ForrestGump]

Go ahead and replace the impeller. One can inspect fine and still not pull water effeciently. 

[eleeski]

My impellers last about 2 years. Failure is exactly as you describe. When removed the impeller looks fine but stays bent up or is too flexible. I usually can replace the impeller a few times before the seals start to leak and I replace the whole pickup pump. Impellers cost less than a tank of gas and pickup pumps cost less than a set of bindings. Engines are kind of expensive (and I've ruined a couple from pushing the life of a crappy impeller). I hate it when the oil gets milky from the water leaking through the head gasket. Either replace the impeller or replace the whole raw water pickup pump ASAP.

Thermostats do fail but usually they fail open so the engine never heats up. Low power, poor fuel economy and stinky exhaust are the effects I've seen from my failed thermostats. Thermostat replacement is a bit tougher than the impeller but still pretty easy. And not critical if you delay. Of course if it doesn't open at all the engine will overheat - especially under load. An immediate fix is called for.

I've never seen the engine waterpump fail (except by leaky seals or worn out bearings). The engine waterpump always seems to cool properly even in unflushed salt water boats.

The other problem with overheating I have seen is when the manifolds plug up. Usually it is the elbow that scales up so water can't flow through. This manifests at high speeds most. I've been fooled by having the boats trick fine but overheat at slalom. If I don't fix the problem promptly (clean out the channels with some welding rod) the rust splits the manifold  - now I must fix the problem promptly. Elbows are not too expensive - just use a lot of anti sieze on the bolts so they don't break coming out the next time. If you do replace the manifolds, again use a lot of anti sieze on all the bolts (especially the head bolts). The broken bolts can be more expensive and time consuming than the parts.

I have three boats in brackish or salty water that can't get flushed. Cooling system problems are significant and totally unrelated to hours. Maybe the boats that don't run often are worse.

Good luck,

Eric

[RobaloGator]

Great feedback. Thanks! One final question. I've looked online for an impeller for the raw water pump (Indmar 68-5001) and find many different impellers. It seems a little confusing. Where do you guys call to order replacements parts for your inboards?

[RobaloGator]

You guys were so right! Here's a 19 year old impellor that sat for the last 12.

[skibug]

http://www.skidim.com/

Discount Inboard Marine.

Call them if you can't find the exact match on their site.  They have excellent tech support.

[RichardDoane]

That'll  be a $25.00 donation to your local foodbank for our "Online Tech Support" !

[D Wolters]

RobaloGator,

Be sure to find all the missing pieces, best thing about Inmar is the Tranny cooler is the next part in line. Be sure to remove the hose in between the two and check there as well.

[Gern Blanston]

I think elee hinted at something that might also be an issue.  The seals and gaskets tend to dry out when an engine sits for lengthy periods of time.  I don't believe that will necessarily relate to overheating, but you could be losing compression and or leaking oil or water to places it shouldn't go.

 If you ski in places that's weedy (a problem for me) then the intake path can get plugged up with weed chunks.  There's a metal strainer in my boat (Indmar mcx) just above the alternator. 

 Do you have a "fake a lake"?  It's like a toilet plunger with a hole in it for a hose.   You can run the boat in the driveway without fear of burning out the water pump.

[Chef23]

We have a weed problem at my lake and when my impeller just went we dug a lot of weeds out of the strainer above the alternator.

One of my neighbors just had his impeller pump go bad which I had never heard of before.  Unfortunately it was the third thing in his replacement list after the impeller and the water pump.

[Gern Blanston]

Chef -

 I sucked in a candy wrapper of all things.  It covered the strainer holes and caused my water pump to blow.  because of that, I put an inline strainer in prior to the impeller.