Engine Overheating

[sheyski]

We have a 1994 Prostar 205 with the Corvette LT-1 engine. We've had over-heating issues with the boat ever since we bought it, where it acts like one of the 2 thermostats stick and overheats when you first warm up the boat. About the time we idle out of the no-wake zone in our cove, the engine gauge is up to the highest mark (220, I think?) and if I give it some gas, the water seems to finally run through the engine and cool down. Life is great. We call it "burping the boat". We do this every time we take the boat out and have been doing it for 4 years now.

We've replaced the impellor and we have purchased 4 new thermostats (2 thermostats, 2 different years) and 1 year we thought the problem was fixed until the boat lost power (the gauge didn't read hot either). Turns out the water was boiling inside the engine. After the engine cooled down, we idled back to the marina and put the old thermostats back in and we've been using them ever since, even though the initial problem is still occurring.

The other problem that started last year is when we are idling after running the boat for a period of time. If we have to idle in a no wake zone for a few minutes, all of a sudden the engine heats up again. In some areas (like going under a bridge at the lake of the ozarks), the no wake zone is long enough that we get really worried that we're going to make it through the area before damage happens.

I would really like to try and buy another set of thermostats to see if we were just unlucky and bought bad thermostats twice in our lifetime. Anyone have any suggestions on what else we could try?

Thanks so much!

[etduc]

Did you check for obstructions, at you tranny cooler? Raw water hoses? All water hoses? (They collapse, sometimes) Do you have a raw water intake filter? (Not all have them.)

I'd check those items first. When you run it, on the trailer, with a fake-o-lake...Do you get approximately the same amount of water, out both exhaust pipes?

[sheyski]

Did you check for obstructions, at you tranny cooler? Raw water hoses? All water hoses? (They collapse, sometimes) Do you have a raw water intake filter? (Not all have them.)

I'd check those items first. When you run it, on the trailer, with a fake-o-lake...Do you get approximately the same amount of water, out both exhaust pipes?

Well one of the hoses does appear to be somewhat flat in the bend. We are wondering if that could be affecting it. We have checked all hoses and I believe the raw water intake filter. Not sure about the tranny cooler though. I'll have to ask.

The only way we've been able to do a fake-o-lake is to plug a hose in the bottom of the boat where it would normally suck up water. Is there actually some sort of contraption we can buy that would work better for testing problems?

Thanks for the suggestions!

[etduc]

This are two ways, to run the boat on the trailer.

The original: http://www.skidim.com/products.asp?dept=1046, And what most of us use: http://www.skidim.com/prodinfo.asp?number=DP7, this one is installed before your strainer.

www.skidim.com is a good place to buy hoses, and ask questions. If one of your hoses is flat or easily squeezed in, it may be the culprit.

[thatsmrmastercraft]

There are a group of us that use a bucket or tub supplied by a hose. Just a matter of getting a hose from the transmission cooler intake to the bucket.

[etduc]

Okay, there are three ways.

[thatsmrmastercraft]

Okay, there are three ways.

[mgs96ps]

......

[ricford]

You may already know this...but the LT1 has reverse cooling....I would make sure that the top tstat has a hole drilled in it for water to pass.

I would also check your circulation water pump.

Plus one on the upper tstat needing a hole. What happens is that until the thermostat opens the heads are getting no cooling. The bypass hole allows enough water through to cool the heads until the thermostat opens. When I bought my 96 it did exactly the same thing and the owner of the marina on our lake knew exactly what the problem was even though he's not a Mastercraft dealer. Pulled it out and sure enough it had no bypass hole. He drilled a 3/16" hole in it and the problem went away.

[mikeg205]

don't forget to check the exhaust hose off the risers... if the are collapsing on the inside it will impede water flow. they can look fine from the outside bit be deteriorating on the inside.

[sheyski]

Thanks for all the great advice. We found an old thread tonight with extensive information and since my hubs is an automotive machinist, he's all gung-Ho on redirecting the bleeder lines based off a service bulletin. We will let you know how it works out!

[mikeg205]

here's the notorious picture...

[sheyski]

We didn't realize that the hoses could collapse on the inside. We are definitely going to check the bleeder hoses for blockage and check the inside of all the other hoses to make sure they are ok as well.

Nasty picture, btw.

[sheyski]

This are two ways, to run the boat on the trailer.

The original: http://www.skidim.com/products.asp?dept=1046, And what most of us use: http://www.skidim.com/prodinfo.asp?number=DP7, this one is installed before your strainer.

www.skidim.com is a good place to buy hoses, and ask questions. If one of your hoses is flat or easily squeezed in, it may be the culprit.

Thanks for sharing these. Looks like I need to add something else to our "buy list".

[sheyski]

There are a group of us that use a bucket or tub supplied by a hose. Just a matter of getting a hose from the transmission cooler intake to the bucket.

Bucket might be a great idea, especially if we are testing at the boat storage area and don't have a water hose handy..but can bring in a couple jugs of water. (Kitty litter bottles are awesome for hauling water, fyi). LOL.