Frost Plug Block heater install tips -
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post #1 of 7 Old 07-09-2009, 08:01 PM Thread Starter
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1989 XJ Cherokee 
Join Date: Mar 2008
Location: Madison, wi
Posts: 625
Frost Plug Block heater install tips

I just installed a block heater in a frost plug on my 89XJ so I figure I'd pass along some of what I learned.
  • The radiator drain plug is worthless, hard to get to and sprays fluid everywhere. Just disconnect the lower radiator hose.
  • watch out for the fluid temp sensor! It's right in the way of the frost plugs and easy to break off (ask me how I know)
  • The rear frost plug is damn near impossible to reach. It's under and behind every conceivable obstacle in the engine compartment. To take out the frost plug I had to get a long steel rod, jam it in there and then hit it with a hammer. At this point about 10 gallons of radiator fluid will fall squarely on your face. Do not try to dodge said fluid or you will ram your forehead into the control arm and then not only be wet but have a knot on your head to.
  • for everyone about to tell me I should have pulled the plug on the engine block to drain it... go to hell, I have an 89, there's no way that was coming out.
  • Do NOT use RTV on the oring. It barely fits as it is, and the last thing you need is something sticky all over it... your hands, the block... you'll spend 2 hours cleaning everything after you realize your mistake.
  • At this point you should check out the instructions on the block heater and realize it says to GREASE the oring... oh... so grease up the oring, the slot for the plug, etc... Good time to also check the frost plug for any scale that might be preventing it from going in all the way.
  • I barely had any room to work in, so I finally got sick of making 1/4 turns for hours on end trying to tighten it and decided to sacrifice my allen wrench. I cut it off so it was about 2 inches long and was a better fit.
  • The key to making it fit is first, grease it well... second, tighten the bolt down until it just starts to get snug but you can move it around... then align it so the oring is seated squarely against the block. Then tighten a turn... and check it again. Keep doing this and hopefully it will suddenly pop in. If the oring pops out of one side, you have to loosen the whole thing up and start over.
  • About this time you will realize that antifreeze is like mosquito catnip. No amount of bug spray can overcome the attraction...
  • My oring kept popping out so I finally got a 1" pipe up in there and pried on each side until it popped in.

Hope this helps anyone else that trys this.
Now I have to go order a new temp sensor... lame.

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post #2 of 7 Old 07-09-2009, 08:58 PM
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1998 XJ Cherokee 
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Your post made me smile-sorry about your head! Did you make up any swears of your own cuz the normal ones are never enough?
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post #3 of 7 Old 07-09-2009, 09:10 PM Thread Starter
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1989 XJ Cherokee 
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Location: Madison, wi
Posts: 625
no... it was more like gurgling and sputtering. Hit myself squarely in the slowing spreading bald spot I keep telling my wife is just a cowlick.
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post #4 of 7 Old 07-09-2009, 09:16 PM
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1999 XJ Cherokee 
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Location: North Carolina
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I almost took out some teeth on the LCA mount back when I was messin with the CPS...i know the pain

'99 XJ Sport
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post #5 of 7 Old 09-22-2010, 12:52 PM
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1998 TJ Wrangler 
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Location: Fallon, Nv.
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Just about to try it on a 98 Wrangler, thanks for the laughs and advice.
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post #6 of 7 Old 09-22-2010, 02:14 PM
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1991 XJ Cherokee 
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Fellow Jeepers feel your pain, share your anguish and revel in your ingenuity!

Now, on to the next mod!
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post #7 of 7 Old 11-10-2011, 12:28 PM
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2000 XJ Cherokee 
Join Date: Jul 2009
Location: Detroit
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Engine block heater install on XJ with an inline-6

I posted how I did this on my 2000 Cherokee XJ over at the Wrangler TJ forum. There are a lot of good posts in that thread that will be very useful. Here's the link to my post:
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