Anti freeze leak but no pressure drop

[northern]

Engine 5.7 V8 closed anti freeze system. Engine is in my jetboat.
Engine had not run in 2 years. Started up well. Engine has 50 hours on it.
Took 2 quarts of anti freeze during warm up. Anti freeze bubbled during warmed up, stopped after warm up.
Engine continues to use anti freeze.1" an hour in heat exchanger. Let engine idle 1100 RPM and added 1" of anti freeze an hour. Have not run boat on lake yet.
Took end caps off heat exchangers. Blew all raw water out with compressed air.
Pressured up heat exchanger and entire engine to 10PSI let sit 2 hours. Pressure did not drop. No anti freeze came out exchanger tubes.
Pressured up to 7PSI that is rad cap pressure and no drop in pressure.
All pressuring up done to cold engine.
Any one have comments or idea what I should do next or what the problem could be.
Any one know how high I can pressure up anti freeze system and not damage parts?

 

[2000SR380]

First, I would not pressurize the system more than the recommended cap (Probably 15 lbs). Anti-freeze "bubbled during warm up" can be a sign of head gasket trouble or a cracked head, but more likely just pushing out air caught in the system. You can get a bulb tester to check for Hydrocarbons or C02 Gases in the coolant at your local auto supply. The odd part of this story is the pressure did not drop from 10bs during your 2-Hour test, but lost 1"of anti-freeze in one hour of running the engine. The easiest solution is you are filling the coolant right to the top every time and the overflow bottle is not working. Somehow losing coolant into the bilge, instead of returning it to the engine on cool down. Next, think about where the coolant is going. If you had a water pump failure, or a hose failure, the coolant leak should be visible (and probably leak down under cold pressure). One possibility is the heat exchanger is expanding when hot allowing coolant to leak into the exhaust side of the raw water system. This would explain 'only leaks when hot' and 'no visible coolant leaking'. Might be worthwhile to remove the Heat Exchanger, and have it tested at your local Radiator shop?

 

[northern]

2000 thanks for response.
The rad cap is 7PSI rated. Is 15 PSI too much for the system.
Good point that heat exchanger leaks when hot does not when cold.
Looked every where for a leak.
Can not smell anti freeze in exhaust.
Next stop rad shop.

 

[dpmulvey]

Air in system?

 

[2000SR380]

2000 thanks for response.
The rad cap is 7PSI rated. Is 15 PSI too much for the system.
Good point that heat exchanger leaks when hot does not when cold.
Looked every where for a leak.
Can not smell anti freeze in exhaust.
Next stop rad shop.

I am mainly a car mechanic(spent 16 year as a Journeyman line mechanic for Chevrolet), but 15lbs is a safe test pressure for almost every car. 7lbs seems a little low. I would have to bow to a marine mechanics opinion on the recommended pressure, but I would feel safe testing at 15 psi. The point is, if the cap gives up at 7psi the system should never develop 15 psi, so testing at more than 8 or 10psi stresses the system more than necessary.

 

[northern]

Thank 2000
Pressured up system on cold engine last night to 10PSI. Let it sit all night. No leak in heat exchanger tubes. Pressure dropped to 9 PSI, temperature went dow10c or 20F from a high in low 60ies.
Put end caps on heat exchanger, filled rad and reservoir to low mark. Ran engine for 1/2 hour. Fluid in reservoir went up 3/4" above the mark it was at when the engine was cold. Let engine cool and level in reservoir was down 1/2" below the low mark. Filled reservoir to low mark and ran up engine to temperature, did not open rad cap. Fluid level went up 1/2" in reservoir. Will report tomorrow when engine is cold where the reservoir level is at.

 

[Xplicitlnck]

I had the same symptoms on my 454. Changed the heat exchangers and it went awayaway. I was losing about 2 inches a dragon out of the res bottle with no signs of atf in the bilge or engine.

 

[northern]

Thank you all for your help.
Ran engine up to temperature. Reservoir went up 3/4"
Engine cooled down and reservoir did not drain back into heat exchanger and exchanger level down.
Going to replace heat exchanger.
Will report results. Will probably be mid June.