Ray H
NAXJA Forum User
- Location
- Falling Waters, WV
4.0/ auto in 96 XJ with 123000 miles.
Last fall I started hearing a knock that sounded as if it was coming from low in the engine. Its not the lifters, or injectors. The knock can be heard inside the passenger compartment as well as outside. It increases and decreases with engine RPMs and it only knocks when the engine is cold, most noticably when the temp is real cold like on a winter morning. When the weather is warmer it can hardly be heard and after warmup, it cant be heard at all. The oil pressure stays steady at 50 when cold or above idle and 30-40 when warm at idle. Fresh oil doesnt change the sound. I went around the engine with a dowl but cant seem to isolate the noise although it does sound loudest when the dowl is against the bellhousing but now that its warmer out, its harder to hear. I pulled the inspection cover today and checked the flywheel/TC bolts and they were all tight (one of them was not as tight as the others but wasnt real loose either). I checked the flywheel well, by prying on it and looking closely with a powerful light, for cracks and found none. I also checked that the flywheel/crank bolts were tight, as well as I could without removing the tranny, by prying on it and then watching it for trueness while it ran and didnt see anything unusual.
I havent completely ruled out an exhaust manifold crack but Ive looked it over well and felt over it while running and havent felt any exhaust escaping.
Thats the history and situation.
My questions now are: If its a rod or piston slap, will I be able to isolate it easily with the dowl and exactly where should I listen and would it disappear when warm? Ive always thought that a rod knock got louder as the engine warmed up and oil got thinner.
If the manifold is cracked, where exactly do they tend to crack?
Sorry this is so long, but people (myself included) tend to get upset when only given part of the story. I did search but couldnt find my symptoms or an answer to my questions
Thanks
Last fall I started hearing a knock that sounded as if it was coming from low in the engine. Its not the lifters, or injectors. The knock can be heard inside the passenger compartment as well as outside. It increases and decreases with engine RPMs and it only knocks when the engine is cold, most noticably when the temp is real cold like on a winter morning. When the weather is warmer it can hardly be heard and after warmup, it cant be heard at all. The oil pressure stays steady at 50 when cold or above idle and 30-40 when warm at idle. Fresh oil doesnt change the sound. I went around the engine with a dowl but cant seem to isolate the noise although it does sound loudest when the dowl is against the bellhousing but now that its warmer out, its harder to hear. I pulled the inspection cover today and checked the flywheel/TC bolts and they were all tight (one of them was not as tight as the others but wasnt real loose either). I checked the flywheel well, by prying on it and looking closely with a powerful light, for cracks and found none. I also checked that the flywheel/crank bolts were tight, as well as I could without removing the tranny, by prying on it and then watching it for trueness while it ran and didnt see anything unusual.
I havent completely ruled out an exhaust manifold crack but Ive looked it over well and felt over it while running and havent felt any exhaust escaping.
Thats the history and situation.
My questions now are: If its a rod or piston slap, will I be able to isolate it easily with the dowl and exactly where should I listen and would it disappear when warm? Ive always thought that a rod knock got louder as the engine warmed up and oil got thinner.
If the manifold is cracked, where exactly do they tend to crack?
Sorry this is so long, but people (myself included) tend to get upset when only given part of the story. I did search but couldnt find my symptoms or an answer to my questions
Thanks
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