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Knock on startup, should I drive it?

crazyoffroader

NAXJA Forum User
Location
Seattle, WA
I just bought a '91 XJ with 235k on the OO engine, and it makes one heck of a racket on startup, but seems fine afterwards.
I only paid $200 flr the truck, and towing it home is cost prohibitive for me ($200 + $10 x 50 miles), so I was wondering if I could just drive it hole? It only knocks on startup, not audible at up to 3k rpm and seems to idle fine otherwise.
Oil presrure°sender Hq bad so oil pressure is unknow>+
Is there a band-aid fix for this problem so I can get home?
Thanks in advance.
 
Re: Knock on startu ) should I drive it?

drive it!i bought mine over a year ago(also a 91 with 4.0 H.O.)and when i bought it i was told it was a lainàbearing~i h`ve tivdn iô#like this for a year now with no loss of power,just an annoying st`rtup% ive been vaitxog for xu to fail but this thing is a t`kk!ya gotta love the durability of these things
 
I think all the 90's to about 94 had piston slap that sounds like knocking. I'd pop a new sender on there, see what the pressure is like and drive it home. If it's low drain the oil and put some 20w50 in there. Sender just screws off and then put the new one in, it's attached right where the oil filter is. On a 98 it is a bit bigger than a bic lighter with wires attached on the end.
 
crazyoffroader said:
I just bought a '91 XJ with 235k on the HO engine, and it makes one heck of a racket on startup, but seems fine afterwards.
I only paid $200 for the truck, and towing it home is cost prohibitive for me ($200 + $10 x 50 miles), so I was wondering if I could just drive it home?
It only knocks on startup, not audible at up to 3k rpm and seems to idle fine otherwise.
Oil pressure sender is bad so oil pressure is unknown.
Is there a band-aid fix for this problem so I can get home?
Thanks in advance.

Your lifters are probably slow to pump up from startup but once they've gotten enough oil, they quieten down. It's really only a nuisance rather than a problem. You could try flushing the crankcase with flushing oil to get rid of any sludge or other contaminants, then refilling with fresh oil and install a new oil filter.
 
I'll second this one. When we got ours in December, it had the same rattle at startup for a couple of seconds until the oil pressure came up. Had a cheap filter on it at the time, changed oil and put a Wix filter on it, now it's quiet at startup unless it sits for a few days.
 
Yep, piston slap or lifters, I rebuilt my 4.0 about 15000 miles ago, and it has knocked on startup since new, I was really worried at first because I rebuilt it due to a spun rod bearing which is what this sounds like. It only does it for maybe one second just when I get that high idle from a cold start, I don't think you have anything to worry about as long as you have good oil pressure.

Josh
 
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