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Unread 04-18-2009, 04:56 PM   #1
xjarchaeologist
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Oil Pressure Drops to 0PSI When It's Warm

So I recently just had my head replaced, and they replaced the oil pump as well. When I'm driving down the interstate, the pressure drops a little bit. But when I got OFF the interstate and was sitting at a stop light, the pressure drops to 0 and the "Check gauges" light goes off. Could it be a bad sending unit, or am I looking at even more money (I've spent $2100 already).....

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Unread 04-18-2009, 05:08 PM   #2
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Since I have already had to replace my head from cracking and eventually the entire engine, I have now have a little expertise in the area. The weird thing about your situation is that the low oil pressure came AFTER the head was replaced. Was your head actually cracked or did you simply do the swap for peace of mind? If the head was cracked, how long did you drive it with the syptoms before you got it fixed? I drove mine almost 12,000 miles before I finally realized I had a cracked head. That amount of driving and coolant in the block was devistating to my engine. After I replaced the head my oil pressure improved slightly but eventually went back to where it was at before. Once it got hot the oil pressure would drop to zero at idle. I now have a reman motor I droped in it and the oil pressure it perfect at all times.
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Unread 04-18-2009, 05:09 PM   #3
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Quote:
Originally Posted by bhicks View Post
Since I have already had to replace my head from cracking and eventually the entire engine, I have now have a little expertise in the area. The weird thing about your situation is that the low oil pressure came AFTER the head was replaced. Was your head actually cracked or did you simply do the swap for peace of mind? If the head was cracked, how long did you drive it with the syptoms before you got it fixed? I drove mine almost 12,000 miles before I finally realized I had a cracked head. That amount of driving and coolant in the block was devistating to my engine. After I replaced the head my oil pressure improved slightly but eventually went back to where it was at before. Once it got hot the oil pressure would drop to zero at idle. I now have a reman motor I droped in it and the oil pressure it perfect at all times.
It was remachined and then cracked (or it could have been cracked the whole time, the machine shopped sucked). I drove it on 2 good sized road trips and little more, so probably 1500ish miles I'd say? I'm worried it's bearings!
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Unread 04-18-2009, 06:03 PM   #4
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Well, I went out and checked the oil level, and it looks maybe 1/2 to 1/4 of a quart low. It's below the add line. The mechanic hadn't screwed the filler cap on all the way when I had picked it up, and there was some oil spillage over the top (at least when I stopped). Guess I'll top it off and see what happens.
I don't know if they used conventional or synthetic. Is it OK to just add one, or should I call them so I can use the same thing?
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Unread 04-18-2009, 07:35 PM   #5
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You can mix Synthetic & conventional with out issues.
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Unread 04-19-2009, 12:49 PM   #6
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I would put a mechanical gauge on it to double check readings. Coolant does very bad things to bearings in no time at all. There is always hope though. Good luck.
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Unread 04-19-2009, 02:30 PM   #7
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I would also check the pressure with a mechanical guage to verify there is a problem. The sending units are subject to failure, but no need replacing a good one.
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Unread 04-19-2009, 07:45 PM   #8
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Well, I topped it off to it's in the "Safe" zone on the dipstick and have been driving it pretty hard all day, and I've had no problems with it. I might just wire up a mechanical gauge anyways to be on the safe side this week while I doing the lift. I'm driving to Nashville on Saturday, so that should be a good test to see if everything's running properly. Only bad thing? THERE'S WATER IN THE FLOORBOARD! (passenger side). After $2100 worth of engine work, a busted heater core is the LAST thing I need. Maybe it's just all the rain we've had today....?
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Unread 04-20-2009, 05:47 PM   #9
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Water or coolant? Coolant is bad, water on the other hand sucks, but water leaks on XJ's in a common thing.
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Unread 04-20-2009, 06:54 PM   #10
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Quote:
Originally Posted by LilRedDakota View Post
Water or coolant? Coolant is bad, water on the other hand sucks, but water leaks on XJ's in a common thing.
It looked clear and didn't smell..anti-freezy (and believe me, after a bad head, you KNOW what it smells like). It was pouring rain, so I'm gonna chalk it up to..rain...
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Unread 04-22-2009, 09:44 PM   #11
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OMG I am among friends!!! I had the same problem (2005 grand cherokee v-6). Head cracked at 48,000 miles then 30,000 miles later blown head gasket. A month later my oil pressure light came on at idle speed (at redlights etc), had the sending unit replaced, and now...well now, my engine stopped running on the highway last night. Aamco did the work too, and they say its my fault.
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