Bubbling back into overflow coolant tank ?

Question

I have a 89' S-10 with a 4.3 v-6 , after you shut it off, the coolant in the overflow tank starts bubbling . This goes on for about 4-5 min. and then stops . It also sounds like the engine 1/2 misses every once inawhile during idle. Why I say 1/2 miss , is that it doesn't miss as to where the engine shakes alot as in a definate spark miss. I hope I made this clearer than mud. Anyone have any ideas as to what is wrong ? I just replaced the sparkplugs tonight as it had been awhile and they actually looked pretty good. Thanks, Iowa883

roger · Accepted Answer

Don't know about the miss but the bubbling in the overflow tank sounds like it could be hot compression gasses escaping out of the radiator cap into the overflow (I have a car with this same exact problem). Does the coolant in the overflow tank smell like burned gasoline? That might help confirm this.

Mike Walsh · Answer

If exhaust gasses get into the cooling system the coolant will be forced outwhile the engine is running.The main reason for overflow tanks is that there are hot spots in the enginethat will cause a small about of coolant to boil after the engine is shut off,forcing coolant out into the overflow tank. This can be aggravated by anyoverheating problem, low coolant system pressure, or low concentration ofantifreeze.roger wrote:

Bubbling back into overflow coolant tank ?

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