I have a '92 Aerostar. I understand for this year the engine block id is #90TM. I see that was good thru '94 and in the '95-96 models the block id is #95TM. Can anyone tell me the differences other than the pistons and if there were any improvements made just in the short block assy?

I have one needing to be rebuilt and want to know if it would be advantageous to go with the later model.

 

This should answer any questions:

Rebuilding The Ford 4.0L Pushrod V6, Doug Anderson, Automotive Rebuilder, April 2001

 

That is a very informative link! Now the question is can a complete newer 4.0 be made to work in an older Aerostar.

 

yes it was very informative. looks like there could be some mixing up of various parts to end up with a better 4.0

 

I think the simple answer is that it can't, but it depends on what years exactly. Somewhere in that article, the author mentions that the new cylinder head design won't work with the older computer calibration.

Of course, with some (a lot of?) work, you could probably get the newer engine to function properly in an older Aerostar but it might involve computer and wiring changes and much more. As cars get newer it gets harder to do swaps because of the increasing integration. What used to be a standalone engine controller now is involved in functions like the transmission, windshield wipers, lighting, instrumentation, etc. This doesn't make things easy for those who like to do swaps and such.

 

In order to get the newer updated head to work with the older computer, the older computer would need to be reprogrammed, basically you would need to pull about 10 degrees off the entire timing map. Its definitely NOT a worthwhile effort. Stick with what you have as there are not enough benefits to justify updating to the later model.

So are you rebuilding you old engine, or getting a junker motor and rebuilding that?

Some problem areas you WILL find have to do with the cylinder heads, and valvetrain. The heads have factory flame hardened seats, which do not hold up. I have pulled these motors apart with just 120,000 miles on them, and all of the exhaust seats are already worn out by that point. There are aftermarket heads that have hardened steel inserts on the intake and exhaust seats which solves the problem. If your old heads aren't cracked, then you can have hardened seats installed, any machinist can do it. Just make sure when comparing the price of new heads versus having seats installed is that the new heads have the inserts. If they don't the heads will eventually wear out and crack just like the stock ones do, but probably faster.

Secondly, a lot of the valvetrain noise is caused by wear in the rockers and pushrods. Ford did not provide those ares with enough lubrication. In most cases you will end up replacing all the pushrods, and you will have to look at the rockers to determine if they need to be replaced as well. There is not a lot that can be done to improve the lubrication issues. But you can prevent of slow down the wear by using better lubricants. For starters, when assembling everything, use a high zinc assembly lube right on the ends of the rods. Also use a break in oil that has a high zinc content. I personally use Joe Gibbs, but I hear that Amsoil makes a great break in oil too. The idea is that the zinc coats and provides a sacrificial protection on the parts. Oil just gets forced out by the pressure, and does not protect the pushrod ends, but zinc has a much higher film strength and will not get pushed out. Avoid moly based lubes, like Royal Purple. Moly can protect parts like pushrods, rockers, and cam lobes, but it can damage engine bearings.

Neither block addresses the valve seat or lube issues, so neither engine is better than the other in terms of reliability. The later motor uses a different piston and a different combustion chamber shape that produces a faster hotter burn, so the computer uses less timing to produce roughly the same amount of power as the old motor, with lower emissions. If you use the later motor on the older computer, the excessive timing causes knocking and pinging and the motor will melt its own pistons.

I recently rebuilt a 4.0L. I used a 1997 block because the '95 block was junk (had something wrong with one of the cylinders, had scuffing and damage), but '95 heads. I had to buy new '95 Pistons because the old ones had aluminum shrapnel embedded in them (hence the scuffing). I used the '95 crank and rods, but the '97 camshaft. Anyway, long story short, there are not a lot of differences other than the heads and pistons. Same motor otherwise. The motor went back into my mom's '95 Aerostar.