White smoke

My bud has an '89 with the 4.0L and it recently started giving off white smoke. But only after it has warmed up. Is there anyway to tell if it is the head that is cracked or it the block is cracked while they are still installed on the truck? It is not a billowing white smoke but it doesn't look like regular condensation smoke either.

Check your dipstick for milky sludge, first, before you vote for the new pope.

could be a blown head gaske.. but yeah.. what colors the oil?

A proper compression test will help diagnose this one, at least it will narrow down if it's a head gasket or a crack. Now as to whether it's a crack in the head or the block, that will require disassembly. However, it's VERY rare to crack the block, unless you do something like put a con rod through the side of it!

First cause for white smoke is USUALLY a head gasket having eroded, which is now weeping coolant into combustion space. A compression check will tell you which cylinder, but not whether it really IS the gasket (fairly likely) or the head being cracked (fairly unlikely.)

I'd put my money on it being a head gasket, simply because Iron heads don't crack as often as I've known aluminum heads to, and the alloy that AMC specified for the 4.0 has a high nickel content, is the same alloy MOPAR used on Hemi blocks, and is just harder than the hinges of Hell. The chance of having cracked the head is about the same as getting hit by lightining, unless you've managed to have a whole slew of overheat or detonation problems...

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sounds like it is time for some Bars Leaks

JJ13 said:

sounds like it is time for some Bars Leaks

Click to expand...

I would NOT recommend doing that. Although Bars Leaks MAY seal the leak, it also plugs up any narrow passages in the RADIATOR. Then you really will have overheating. The XJ's cooling system is not very tolerant of reduced coolant flow, and Bars Leaks will do exactly that: reduce coolant flow!

Thus the smiley face after my comment. It isn't a recommended fix for a blown head gasket. You do know that 95% of new vehicles come with bars leaks or some similar product in them from the factory. In addition most machinists put a block of ceramic seal in behind freeze plugs when they rebuild engines. Those products generally only gum up the area around the leak. They don't stick to the walls of the tanks and tubes in your radiator. The fresh rebuilt radiators in our Locomotives at work get a 5 gallon bucket of Bars Leaks when they are put into service.

Hate to admit this, but do these XJs have any type of vacuum connection to the auto trans's? ATF into the engine will also cause white smoke exhaust. Jut thought i'd throw this into the mix-

No - the AW4 is electronically shifted and lacks the "vacuum modulator" found on Big3 slushboxes (hey, it's a Toyota design!)

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