OVERPRESSURE IN COOLING SYSTEM

The radiator split a seam and I removed it and had it recored. After putting the radiator back in I flushed the system. The problem started right off. The cooling system pressurizes and when you shut
the engine off it blows bubbles in the overflow tank. The system will stay pressurized for at least two days without starting the engine. While driving the temp gage will go almost to the red line and then return to the normal range. It only does this little trick once each time you drive it. There is no sign of coolant in the oil and no oil in the coolant.
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First of all replace the cap if you have not already done so and I would suggest a lower pressure cap because you do not need a 16PSI cap to begin with with proper coolant. Stant makes a 13 PSI one and a 9 PSI one as well. I have been using the 9 PSI ones for many years and I have had no cooling issues even in 100 degree plus heat nor on Pikes Peak. Second, coolant does normally expand when it heats up and will purge into oveflow tank and when you shut off a hot engine is can actually increase coolant temps for 5 or 10 minutes and cause it to purge further so this is normal. Third if the system is not properly purged of air it can get a air slug that can impeded cooling and cause pump to cavitate too. When it heats up it purges into overflow and as it cools and contracts it sucks coolant back into system to replace any air that may have been burbed out (this is reason overflow tank needs to be keeps full) If you remove cap and relieve pressure you break the automatic purging cycle. Forth, if you feel you have excessive pressure building all the time, you could have a bad head gasket that is letting combustion gasses into cooling system and causing it to pressurize excessively and inducing air slugs that are impeeding cooling. ----------------- TheSnoMan.com
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SnoMan Thanks for the info. I failed to mention that this is a 6.5 turbo diesel. I assume from the last comment you wrote that I could have a bad head gasket and not find contamination in either oil or coolant.
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Yes you sure can. A crack in cylinder or head in waterjacket area can cause it too. There is a LOT of compression in that engine to contain. Not all blown head gaskets leak/mix oil and coolant though they generally tend too. ----------------- TheSnoMan.com
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wrote:

You can swing by your local auto parts store and get a kit to test the coolant for hydrocarbons. If you get a positive then you have a leaking head gasket if you do not get a hit then it is something else. When I read you post I initially though head gaskets...
mark
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get the tester .. you screw it on to your rad, pump it up to like 10-14lbs and if it starts to drop roght away.. you have problems.. if it stays steady for at least 2-3 min then you have an air lock or rad cap problem . HELL your water pump may be bad if it is over heating..
wrote:

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Old school tester is as follows. Remove radiator cap when cool Remove coil wire (so it won't start) Place hand over the hole where cap goes Have someone crank engine over If you feel pressure as cylinder strokes compression ....you have a blown head gasket.

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6.5TD crack between exhaust and intake valve, also head gaskets. mostly pre 99 or 98 they went with better cooling in or after 98. Have the cap tested first, it should relieve any pressure above it's rating so you shouldn't have split a rad to begin with. You say it blows bubbles into the tank after you shut it off, head gasket or cracked head should be making bubbles while running. Also you say it holds pressure for two days or more so that kind of says no leak. Sounds like it has an airlock. What year is yours ?

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