OMC Stringer 800 overheating

I am new to this forum and am looking for some advice on an overheating issue. I will do my best to summarize everything I have tested.

I have a 1978 Glastron Carlson CVX-18 with a 305 V8 and a OMC Stringer 800 outdrive.

I was having carburator issues so I replaced the stock quadrajet with an edelbrock and had been doing all the testing with a hose hooked up directly to the outdrive with the adapter the allows you to attach the garden hose directly. (forgive me I don't know the proper term)

I had resealed the outdrive and replaced the water pump in the summer of 2013 and only ran the boat on shore with the garden hose due to the carb issues I was having. I replaced the carb in May 2014 and have been running it on shore with the garden hose and I hadn't had a problem overheating until I mistakenly ran it with the water shut off so the motor wasn't getting any water. The motor was running and I didn't notice it getting hot until I happened to turn around and look at the temp gauge and it was reading 250 F. It ran for about 10 - 15 minutes without water before I noticed the temp. I turned the motor off and let it cool down for several hours before attempting to restart it and it started up fine and did not overheat (ran at about 160 F) with the garden hose attached. NOTE: I did not turn the garden hose on once I realized I had overheated the motor because I didn't want to give a hot motor a shot of cold water for fear of cracking anything.

I put the boat in the water this weekend and within about 3 minutes the motor was already up to 200 F. I made it back to shore and shut the boat down and at that time the temp was 210 F.

After the boat cooled back down I hook the garden hose back up to it and again it ran at about 140 - 160 F.

Some additional information:

- The motor runs fine with plenty of power
- There is no water in the oil
- After it overheated in the lake I did check the thermostat and it was very rusty so I removed it. I did not replace it with a new thermostat as I did not have one available
- I pulled the fresh water intake line off the thermostat housing and it was pumping water out when the boat was in the lake (not hooked up to garden hose). It appeared to be a good stream of water but I don't know how much is supposed to be coming out of there so I can't say if it is pumping enough.
- I stll have the adapter plate that allows you to hook a garden hose up to the drive attached to the boat and have simply put a cap on the hose connector. I assumed it was ok to run it this way but if it is not please let me know.
- Prior to having all the issues with the boat it would never get over 160 F when it was in the lake.
- I live in Minnesota so the boat has only ever been in fresh water.

I assume there is a chance that I ruined the water pump by running the boat for about 15 minutes without any water but the fact that it is pumping a decent stream of water leads me to think it maybe something else.

Before I dig into tearing about the outdrive again to replace the water pump I was wondering if there is any other tests I should do or what else could be causing the overheating. I am worried that I may have blown a head gasket or warped the heads. Is there any chance the exhaust manifold could have cracked and be causing this issue?

I appreciate any advice/assistance you can provide.

Thank you

Dan

I hope that I included all the necessary information but if there is any other info you need please let me know.

cvx18 said:

I assume there is a chance that I ruined the water pump by running the boat for about 15 minutes without any water

Click to expand...

yep, that chance is 100%
I have seen them survive 30 seconds and even 90 seconds if recently wet.
15 minutes? I'm surprised it didn't start your boat on fire.

Are you sure it went 15 minutes with no water? I can't see how your exhaust couplings didn't melt or burn about the 7 minute mark.

If it was 15, I would start with a pressure test of the engine and cooling system- and a compression test of the engine. I would be very suspicious of heads and head gaskets surviving that.

hystat said:

yep, that chance is 100%
I have seen them survive 30 seconds and even 90 seconds if recently wet.
15 minutes? I'm surprised it didn't start your boat on fire.

Are you sure it went 15 minutes with no water? I can't see how your exhaust couplings didn't melt or burn about the 7 minute mark.

If it was 15, I would start with a pressure test of the engine and cooling system- and a compression test of the engine. I would be very suspicious of heads and head gaskets surviving that.

Click to expand...

Thank you for the quick response.

To your question about 15 minutes... I cant say for sure how long it was but it was certainly over 5 minutes as we were messing with the carburator getting it adjusted during that time.

The exhaust couplings are fine and didn't melt but as far as the heads and head gaskets the only thing I know for certain right now is that the motor was running fine however I know that doesn't mean that the gaskets and heads didn't get damaged.

I have a compression tester so I will for sure check the compression. I had checked it before I installed the new carb so I know what all the cyl. were at before the overheating issue. I am familiar with how to pressure test the cooling system on a car but how do you do it on a boat with the open cooling system they have?

Thank you for the information!

Dan

red x's = remove the hoses from manifolds and clamp a 5/8" bolt in each end
green arrow = introduce air - max 15 psi

and as far as that water hose adapter on the drive goes, those are ok. I prefer the $5 flush adapter. It does the same thing but:
1. you are more conscious of the hose and water when working on the motor.
2. you can loosen the cap any time you start the boat in the lake and get a visual on how your impeller is doing at delivering water to the tstat hsg.