Mercruiser 496 HO problem
10-06-2019, 03:02 PM
#11
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Thread Starter
I have checked for leaks in the oil cooler and headers because its the only way for water to get in to the oil. No leakage, so it cant be seawater in the oil.
I have done a leak down test with cold engine.
Good results with 5-7% leakage on all cylinders.
I have changed the oil in the engine and started it up.
It spins like a cat after cold start.
But when the engine is getting warm (about 60’C) the RPM is starting to go up and down. Its also like a air sucking sound when the rpm goes up. I read about it and it could be the IAC muffler?
Can the IAC muffler be the problem with the bad idle when it gets warm?
I did a leak down test after when the engine was warm.
Good results again, even better results with 4-5% leakage on all cylinders.
Shouldnt the test show if a head gasket is bad?
Because now I havent a clue wear the coolant is getting in to the oil..
Does anyone know what the problem with the bad idle can be? And before I take the head gaskets of, can it be a leakage without any signs on the leak down test?
/Johan
I have done a leak down test with cold engine.
Good results with 5-7% leakage on all cylinders.
I have changed the oil in the engine and started it up.
It spins like a cat after cold start.
But when the engine is getting warm (about 60’C) the RPM is starting to go up and down. Its also like a air sucking sound when the rpm goes up. I read about it and it could be the IAC muffler?
Can the IAC muffler be the problem with the bad idle when it gets warm?
I did a leak down test after when the engine was warm.
Good results again, even better results with 4-5% leakage on all cylinders.
Shouldnt the test show if a head gasket is bad?
Because now I havent a clue wear the coolant is getting in to the oil..
Does anyone know what the problem with the bad idle can be? And before I take the head gaskets of, can it be a leakage without any signs on the leak down test?
/Johan
10-07-2019, 09:12 AM
#12
Registered
The coolant could be coming in from the intake leak, either a crack or gasket. If there is a intake problem this can also impact idle and running.
10-07-2019, 09:23 AM
#13
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Thread Starter
If the coolant is coming from the intake, can it pass trough the leak down test?
Because the test showed no leakage.
10-07-2019, 09:28 AM
#14
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Coolant does not flow through the intake manifold
10-07-2019, 09:29 AM
#15
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You can do a leak down test with the intake off the motor. The test determines leaks in valves and rings
ok
Coolant does not flow through the intake manifold
10-07-2019, 10:03 AM
#16
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Thread Starter
10-07-2019, 11:54 AM
#17
Registered
Correct!! The gen 7 8.1 utilizes a dry intake like the LS platform.
To the OP, use an automotive coolant system tester and pressurize your closed coolant side. If you have coolant in the engine oil, you have a cracked head/block or headgasket. Don't worry about the idle problem now. You have MUCH bigger concerns with coolant in the oil.
To the OP, use an automotive coolant system tester and pressurize your closed coolant side. If you have coolant in the engine oil, you have a cracked head/block or headgasket. Don't worry about the idle problem now. You have MUCH bigger concerns with coolant in the oil.
Last edited by Ryan00TJ; 10-07-2019 at 11:59 AM.
10-07-2019, 02:33 PM
#18
Registered
Thread Starter
Correct!! The gen 7 8.1 utilizes a dry intake like the LS platform.
To the OP, use an automotive coolant system tester and pressurize your closed coolant side. If you have coolant in the engine oil, you have a cracked head/block or headgasket. Don't worry about the idle problem now. You have MUCH bigger concerns with coolant in the oil.
To the OP, use an automotive coolant system tester and pressurize your closed coolant side. If you have coolant in the engine oil, you have a cracked head/block or headgasket. Don't worry about the idle problem now. You have MUCH bigger concerns with coolant in the oil.
I also change the head bolts and intake manifold gasket at the same time.
