Engine cold start tap not obvious after teardown.

Joined
Jul 30, 2003
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2002 Ford Taurus Vulcan 3.0 OHV, 142k miles. Unknown maintenance before I bought it with 96k.

This car developed a cold start tap about 20k miles ago. The colder it is, or the longer the car sat, the worse it would be. It would last 30 seconds to 1 1/2 minutes. No other symptoms. Various oil brands 0W20 to 5W30, Liqui Moly engine flush, no change.

About 5k miles ago it developed a cold start misfire cyl #1 that would go away after about a minute. I swapped plug, plug wire, coil and injector with no movement of the misfire. Last week it got bad enough that it would never smooth out so I dug into it. With about 2 oz of coolant loss per week and a cold start tap I suspected head gasket or bad lifter.

The head gasket does have a small break in it over the misfiring cylinder so I guess that is my stumble.

But, the only loose rocker is cylinder 4. The rocker, rod and lifter on all cylinders including #4 with the loose rocker look perfect to me so I'm a bit nervous about that. I thought I'd find an obvious leaky lifter but cyl 4 as well as all the others remain pumped up 4 days after shutdown. The engine is also clean, no signs of sludge or even heavy varnish so I don't think I have a blocked passage?

Any suggestions on anything else to check regarding the cold start tap? I have ordered a lifter and rocker for cyl 4 just in case something's worn and I can't notice it.

If I button this thing up and still have a tap, it's not getting anymore attention. 😁
 
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Start with the head gasket. You are putting the cart before the horse, I was taught repair what you know is broken first not the symptom.
 
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I think you found your problem. Head gaskets can leak a couple of ways. Some put coolant into an oil passage, and others can put coolant into a cylinder.
While running, the engine then puts exhaust gasses into the water jacket, if it's the latter type of failure. When sitting cold, coolant can get into the cylinder, and the ensuing knock happens.
 

Silver

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Joined
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Start with the head gasket. You are putting the cart before the horse, I was taught repair what you know is broken first not the symptom.
This seemed irrelevant to the tap at first, until I read JohnnyG's comment. So coolant in a cylinder can cause a tap? I had not thought of that, but I guess I can understand the inability to compress the water causing valvetrain noise. It's just that at first, the tap was present but no stumble.
 
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Northstar V8 head gaskets would fail in this way, and "maybe" not tap, but would sometimes steam on startup. Anyway, I'm thinking as the head gasket leak got worse, now you may also be down on compression in that cyl, causing the stumble/misfire.
 
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