I recently replaced the radiator on my DII, in putting it back together I put the thermostat in backwards and over heated the engine. As a rsult now the head is leaking into cylinder 7 and 8. I am going to replace the heads but need to know which ones fit the 4.0. I have heard that the 4.0 and 3.9 heads are interchangable. Is this so? I found some rebuildt ones on ebay for $250 each, sounds like a good price. Any thoughts? I recently did a top end seal job all the way down to the valley so I think the heads aren't much more. What all do I need to get to do the job?

 

That sucks. I'm not a DII guy but why not just machine the heads you have? If it was a DI I could help you out, but the head job on a DII is not in my resume. Good luck! Make sure you put the thermostat in correct this time!!

 

It is a 99 DII, when I did the upper gaskets i noticed that one of the headbolts would not seat to the right torgue. I would prefer to replace the head then try a helicoil.

 

The head bolt seats to the block, not the head.
Don't make a decision about replacing till you can verify if it is the head gasket o or warped head that has the problem, then have it measure for warpage.

 

Take the head to a head shop, that's the best way to check it, they'll usually do it for about $5-$10 a head. If you need new heads i just bought one from specialized recyclers for $100, it was not rebuilt, but my machine shop said that it was in perfect condition and he didn't have to do anything to it..

Also, if your head's not cracked you may be able to have it machined flat. So long as it's not too warped..