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1996 7.4 Gi Coolant Overflow

B

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I replaced the original heater hose to the water heater heat exchanger. I caught two gallons of coolant in a bucket when removing the old hoses and lost a couple of quarts into the bilge during the process. After replacing the hoses I refilled the cooling system through the overflow tank and started the engine.The Volvo owners manual only says "start the engine to purge the cooling system of trapped air". The engine burped and coolant starting running from the cap on the overflow tank. I turned the engine off. Next removed the larger brass plug from the thermostat housing to bleed air. When coolant came out the bleed hole I replaced the plug and added a pint to the overflow tank. I have run the for a few minutes at a time while watching the temperature gauge. The temp. gauge was up to 170 the last run. Each time the coolant everflows from the overflow tank so I remove the excess from the overflow tank, allow the engine to cool and repeat. After doing this four times the coolant is still overflowing. I assume I still have some air in the system. Any suggestion other than repeating the procedure until the coolant stops overflowing?
 
I think that you may be misundertanding the instructions and the purpose of the "Coolant Recovery" system.
The only time that you would add pre-mixed coolant to the "Recovery" tank would be if you were loosing a small amount of coolant.

You lost a LARGE amount when you disconnected hoses, and you lowered the coolant capacity within the engine.
NO amount of added coolant at the recovery tank would have worked!
The recovery system works on a "Expand/Contract" basis, and the H/E must be up to snuff in order for this to function.
The small hose connection must also be near perfect, as this must be negative pressure capable.

To replenish this, you should have added coolant directly to the H/E (heat exchanger).


What likely happened is this:

  • Coolant was now too low to physically contact the thermostat.
  • Engine temp increased and exceeded normal.
  • As mentioned, No liquid was present to open the thermostat.... only steam.
  • Engine temperature incresed to boiling point.
  • Results were puking at the H/E.
With the engine cold, you will want to add coolant directly to the Heat Exchanger, topping it off.
Make sure that both seals in the Pressure Cap are good!
This pressure cap must allow for over-pressure release, and equally important, create a leak free siphon for "Recovery"

Also make sure that the "recovery" tank is up to snuff.
You will probably need to allow the engine to go through several Heat/Cool cycles in order to completely purge itself of air.
Follow this by keeping the recovery system up to the correct level of coolant.

.
 
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Thank you for the information. These are my first closed cooling system engines so I try apply some automobile logic but the cooling system is a little more complex with the heat exchangers, or just different.

Bob
1996 Chris Craft Continental 38
Twin Volvo 7.4 Gi
Hurth V-drives
 
Bob, Good for you.
Youll find that it is basically no different than an automotive radiator system.
Had you drained your car coolant, you'd be re-filling via the pressure cap on the radiator....... not via the "recovery" bottle.
 
I have gone through five fill, run and cool cycles. When I started the engine this last time I immediately looked at the side exhaust tube and could see orange coolant coming out at which time I shut it down.

Could this be caused by a blown gasket or a leak in the heat exchanger? I have observed that the engine temperature has been rising very slowly over ten minutes to 170 and then quickly increases before I shut it down.
 
Picked up the boat from my local marina this evening. Diagnosis: the coolant I had been adding to the heat exchanger after my initial fill through the expansion tank was going into the raw water side of the heat exchanger hence it was being flushed out of the engine on startup. The heat exchanger Chris Craft installed on this boat has no port available for adding coolant to the heat exchanger. The brass plug on the top of the heat exchanger which I had been removing to add coolant is used to allow the raw water to drain from the heat exchanger when winterizing the engine. The coolant can only be added to the expansion tank which is connected by 5/8" heater hose to the freshwater(coolant) side of the heat exchanger. Fortunately my first attempt to replace the coolant by removing the plug in the thermostat housing allowed me to nearly fill the freshwater system. The overheating it turns out was caused by a marginal raw water pump impeller. It was working OK before I started this project, at least as indicated by the temperature gauge, but was just on the edge of being ineffective. The marina replaced the $40 impeller, topped off the coolant, the engine runs as if nothing had happened and I breathed a huge sigh of relief.

1996 Chris Craft Continental 38
Twin Volvo 7.4L Gi with 2009 Michigan Motorz REMAN, Generation 5 Long Blocks
Hurth V-Drives
 
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