I'm rebuilding the top end of my 89 Convertible's 3.9 engine because I have coolant mixing with oil. I'm the second owner of the truck. I expected that the head gaskets were shot but they didn't look too bad when I tore it down. I also can't see any visible cracks in the heads. Does anyone know if the heads on pre-magnum engines were prone to cracking? I'm trying to decide if I get these machined and rebuilt or just order new reman heads for it. Hoping that a head is cracked and not the engine block. The engine ran ok and compression checked Between 120 - 140 PSI at all cylinders. Just blew white smoke and steadily lost coolant so I ripped into it.
Thoughts???

 

Get the heads magnafluxed; that will answer that.

No, I've only heard of LA heads cracking "all the time" from one source, and I BET that he's thinking they're Magnums.

He tried to tell me my 1988 had a Magnum V6 in it ...

RwP

 

Ok. I guess it's the only way to know for sure. Never heard of a pre-91 magnum. Lol.
Thanks for your help as always.

 

Ralph is exactly right. Get the heads magnafluxed. Checking parts & systems is ALWAYS cheaper than just throwing parts at a problem. Also, wouldn't you really like to KNOW what the problem is before you start fixing it? (of course you would!). Always check (diagnose) FIRST, and THEN start replacing parts. (Good Luck!!).... FredT

 

Ok, today I started on cleaning up the block and doing a basic inspection on the heads before I take them to the machine shop for magnaflux etc. As I was scraping the machined surface with a razor, I spotted a crack on the #3 cylinder running between the intake valve seat and a coolant passage. The crack is about 1/2" long and wide enough to see without any aid. So I'm sure I've spotted the cause of the oil and coolant mixing. Don't know the root cause, but I'd assume an overheat with its past owner. Probably why it was sitting in a garage for 8 years before I bought it. Lol. Just going to buy reman heads now and exchange them rather than have these repaired. Thanks for your replies as your pointers keep helping me. I'm having fun with it at least!