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Hawksinkalispell
07-09-2010, 10:15 AM
I have a 1988 Tristar, open cooling system, with a 351 indmar. I had a similar boat in the past 1987 Ski supreme same (similar) motor. With the Ski supreme I used to be able to put my hand on the Exhaust manifolds after the motor was up to tempeture. With my Mastercraft you can touch the exhaust manifolds after the boat is up to tempeture but they are very hot.

I've had my Mastercraft for about 3 or 4 years, I can't remember if I've changed the Thermostat but just pulled it apart last night and it has 140 stamped on it, which I would guess is the lowest temp thermostat they make. One thing that I'm not sure about is it looks like the water pump was replaced at sometime. It's not the painted black like the rest of the motor, it has "Ford" casted on it, maybe it's an auto pump maybe not? Does anyone know if the Marine Water pump is any different then an auto one, other than being painted? I would guess they are the same.

I had some major overheating, raw water supply problems last night, first time out this year (We live in MT) real bummer. Pulled everything apart up to the Thermostat. Hopefully can find some parts today...

oldairboater
07-09-2010, 11:26 AM
Why are you sure that the water pump is the problem? Water pumps are simple to trouble shoot. They leak, make noise but rarely don't pump unless they come apart. I would be looking at my raw water pump and you didn't mention impeller change out in the raw water pump. You can check the thermostat with water, pan, fire, and a reference thermometer. If it looks bad change it for sure but Skidim has your parts and I would stay away from automotive parts if it was me when it comes to engine cooling.

Dad 2 3
07-09-2010, 12:14 PM
Hawks,
OldAir is spot on. However, to clarify if the pump goes and starts leaking it will start coming out of a small hole on the bottom of the pump.

About 8 years ago, I thought it would be prudent to change my thermostat in my Nautique (302/5.0 Ford motor (marine converted by Waukesha Engines)). I made the fatal error of going to the local auto parts store and purchasing a small block Ford 165 Robertshaw thermostat. I buttoned her back up and hit the water. I began having over heating issues that were very irratic (50% of the time). And I tested the thermostat before I put it in with the pan of water on the stove with a thermometer. Above 2500 RPM she ran cool (normal), as soon as I went to idle, the temp would start climbing quickly. I could lower the temp without moving by just putting it in neutral and spinning the motor up to >2500 RPM. Long story short, 4th of July 2002, blown head gasket, and a tow.

Root cause - As I would launch and pull water into my raw water pump, I would pull small amounts of air as well which is common. This air would accumulate and get trapped against the closed thermostat in the engine. As everyone knows, air is a poor conductor of heat and the air would not reach 165 so it wouldn't allow my thermostat to open no matter how hot the water temp would get. When I throttled up, it forced water at a higher pressure against the thermostat and displaced the air which then would allow it to open and all was good. Marine grade thermostats for open loop cooling have a small vent hole (diameter of a paperclip) in the body which allows air to pass through so air doesn't get trapped in the cooling loop. Allowing this tiny amount of air to pass through made the entire difference.

conclusion - Go to skidim and not Napa for the thermostat. There are difference between auto and marine parts in certain cases.

ramzak
07-09-2010, 01:55 PM
Hawks,
OldAir is spot on. However, to clarify if the pump goes and starts leaking it will start coming out of a small hole on the bottom of the pump.

About 8 years ago, I thought it would be prudent to change my thermostat in my Nautique (302/5.0 Ford motor (marine converted by Waukesha Engines)). I made the fatal error of going to the local auto parts store and purchasing a small block Ford 165 Robertshaw thermostat. I buttoned her back up and hit the water. I began having over heating issues that were very irratic (50% of the time). And I tested the thermostat before I put it in with the pan of water on the stove with a thermometer. Above 2500 RPM she ran cool (normal), as soon as I went to idle, the temp would start climbing quickly. I could lower the temp without moving by just putting it in neutral and spinning the motor up to >2500 RPM. Long story short, 4th of July 2002, blown head gasket, and a tow.

Root cause - As I would launch and pull water into my raw water pump, I would pull small amounts of air as well which is common. This air would accumulate and get trapped against the closed thermostat in the engine. As everyone knows, air is a poor conductor of heat and the air would not reach 165 so it wouldn't allow my thermostat to open no matter how hot the water temp would get. When I throttled up, it forced water at a higher pressure against the thermostat and displaced the air which then would allow it to open and all was good. Marine grade thermostats for open loop cooling have a small vent hole (diameter of a paperclip) in the body which allows air to pass through so air doesn't get trapped in the cooling loop. Allowing this tiny amount of air to pass through made the entire difference.

conclusion - Go to skidim and not Napa for the thermostat. There are difference between auto and marine parts in certain cases.


WOW!!! This is SOOOOO IMPORTANT to know. Great info! Thanks!

Hawksinkalispell
07-09-2010, 04:39 PM
The problem last night MOST likely was the Impeller/Raw Water pump, changed, cleaned and to be reinstalled today. Bought a new spare.

I looked and talked with boat place and agree that the water pump should be fine, same design as listed on SKI DIM. By the way maybe Ski DIM should higher some more people or get some more phone lines. I've called 4 times this week and just get thier voicemail, you gotta make hay while the sun shines, applies to boat parts too.

Great info on the Thermostat and the air issue. I did buy a thermostat from a boat dealer, it was a Mercruiser thermo, I'll call them and varify that it has that hole, as I can't remember/didn't look.

Hawksinkalispell
07-09-2010, 04:45 PM
P.S. The inside of my Johnson pump (Raw water) is slightly scored. Thoughts on tolerances? With the splines on the Impeller there still should be a vacum but...

oldairboater
07-09-2010, 05:24 PM
My raw water pump impeller has a front and back ---not sure about yours but I would make sure it is right. I will go one further. I didn't mention it here but all my thermostats have at least two 1/4 holes drilled in them on the body where they are the widest. Learned this trick years ago from boats with radiators mounted remote. Pain in the butt to get all of the air out of the system. I even started doing this on my automobiles. Sometimes makes it take longer to get an engine up to temp but traps no air and always allows some flow---even when they stick closed. Not a recommendation but just how I have done it forever.

EricB
07-09-2010, 05:29 PM
Test the output of the Raw Water Pump.
Take off the hose connection for the raw water pump to the engine recirc pump (keep connected to the raw water pump). Adapt a length of hose/tube (same diameter) that will reach over the gunnel (side) of the boat.
Put boat in lake and start. Observe the output of the RWP. Should shoot a good volume of water that is equal to the i.d. of the hose.
Obviously, do not run the engine long. However, if you want to see the RWP in action, do this test. You'll be supprised how good the pump is witout restriction. On the flip side, if it is weak it wiil not pump much.

NeilM
07-09-2010, 10:53 PM
If the manifolds are hot, they're not getting enough water from the raw water pump. If the raw water pump checks out fine, then check the water lines running to the manifolds (and the fittings at the manifolds) for restrictions.

If the pump body is scored on the inside, I'd replace the pump, just to be on the safe side. I wouldn't want the impeller getting shredded...

Hawksinkalispell
07-11-2010, 11:54 PM
Put it all back together and now getting good cooling/temp ranges. Our water is cold so it is staying right around 140, bumps a little if we run it hard and then let it sit, I'm sure it's normal as the water is now sitting in the motor and heating, fire it up and within moments it's at 140ish.

The manifolds seem slightly cooler, I think there was a bit of a restriction from the gasket on the bypass/exhaust manifold hole on the thermostat neck.

The pump scoring was recessed, not raised so I'm thinking all is good there now.