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scbett57
New User
Jan 5, 2010, 11:51 PM
Post #1 of 4
(4282 views)
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Engine knocks when cold
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I have a 1997 Mercury Sable with the standard 3.0-liter engine with 105,000 miles. The engine knocks/taps once I start the engine while it is cold. Once the engine reaches normal operating temp, the knocking quits. It is a very fast knock and sounds to me like the lifters, although I have not heard what a piston slap sounds like. It also sounds like numerous lifters knocking. Leading up to this problem, I was trying to solve a heater problem, not putting out hot air. I started with the basics, replacing the thermostat (factory temp of 195), flushing cooling system and finally replacing the water pump. The pumps impeller blades were completely corroded away. Surprisingly, I was not having over-heating problems other than occasionally; the temp gauge would increase slightly while stopped for a light or such. Once the water pump was replaced, I noticed the temp gauge still increasing while stopped with the engine running. The reservoir was empty so I bled the cooling system with no change. I was loosing coolant but no leaks. My oil was clean of coolant (no milky foam) but did notice more exhaust than usual and missing at low RPMs. I figured it to be a head gasket and purchased Bar’s Leaks Head Gasket Fix, followed the instructions and have not lost coolant since. A couple of days after the gasket fix is the time when the knocking started. I have just changed the oil, which I do religiously, every 3,000/3,500 miles, and with no change – still knocking. I did not have any of these problems (other than the heater) before I changed out the water pump. What could be causing the knocking and why the problems after changing the water pump? Unfortunately, this has not solved my heater problem, which I am afraid the heater core is bad.
Thank you for replying.Steve
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re-tired
Veteran
/ Moderator
Jan 6, 2010, 3:12 PM
Post #2 of 4
(4264 views)
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Re: Engine knocks when cold
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Its hard for the average person to tell if they have a spark knock (pinging) or lifter bleed down (rattle) . If pinging it could be due to carbon buildup on a high mileage eng . The slight loss of compression by head gasket was fixed with the bars leak . the increased compression is now causeing ping ,,,IF this is the case try some injector cleaner for the next fewfillups. If the cause is lifter bleed down it could be normal wear. If so try going up in the weight of oil , say a 20w/40 or straight 40 , this may help. IMO 3k is to short a mileage for oil change's. I have a 93 chevy pickup with 240k and have changed oil every 5to 6 k since new , using whatever was on sale (always a name brand tho). Recently changed valve cover gaskets , heads were clean , no sludge . But by all means do what your comfortable with .
LIFE'S SHORT GO FISH
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jason32038
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Jan 9, 2010, 4:17 AM
Post #3 of 4
(4248 views)
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Re: Engine knocks when cold
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Sounds like sludge preventing oil flow to the valve train or weak oil pump. Wrong viscosity oil?
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nickwarner
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/ Moderator
Jan 18, 2010, 9:32 AM
Post #4 of 4
(4212 views)
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Re: Engine knocks when cold
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when its only doing it cold, I would guess its your lifters. You can replace them or just run a thicker oil. I have had some success quieting them with Lucas oil. As to your heater, the core is plugged tight with rust. There's a trick you can try if you want to avoid the fun of trying to get that thing out. Unhook the heater hoses from the firewall and put some lengths of hose on it that can reach out of the engine compartment to a pail. Go to Harbor freight or somewhere like it and find a small cheap 12v fluid pump. Get some CLR cleaner too. Circulate CLR through the core for several minutes, then flush well with water. CLR is corrosive so get it all out. Blow it out with air, hook the heater hoses back up and bleed the air out. I did this last week to a 98 Sable that had the same problem and the regular coolant flush stuff couldn't fix it. January is a bad month to be without heat
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Please Help - Knock sound & engine fail
