it's kind of late to jump in to this thread but i had the same problem with my cj7 many years ago. (overheating under load) my radiator was plugged up and i had it boil flushed for $25. worked gteat for a couple years then i had to do it again. i didn't read this entire thread so for all i know, you may have a brand new radiator in there. currently, i have a brand new radiator but no shroud. it gets hot but i know a shroud will fix that. i just don't know where to find one.

thanks for the input. i have had the radiator rodded, but am getting ready to buy a new one, the motor just runs TOO good for it to be a head issue (in my opinion), and i don't wanna tear it down unless i'm absolutely sure that that's the problem. this is a larger motor than i had before by .5 liter, and i suspect the load on the radiator is the issue. by the way, you can prolly get a new , used shtoud from www.collinsbrosjeep.com in Wylie Texas. They are a reputable and reliable when it comes to shipping. Rob

I hope you're right. I have a ford in the driveway that runs great but I cant keep water in it due to a small leak on one head. I acts much like you describe. A very small leak would not necessarily have any noticeable effect on the way it runs. It could however make a bubble that could interfere with circulation causing it to overheat at hwy speeds and blow water out. Even an inadequate radiator should work better with a 50 MPH wind blowing through it, shroud or no shroud. My CJ came with a 3 core rad and a 160 degree thermostat. It wouldn't make enough heat for the heater to work. When I destroyed it by punching the fan into it (another story) I replaced it with a 2 core and put in a 180 degree thermostat. I can Idle around all day in 90 degree weather without overheating. If I speed up at all it goes immediately from 190 down to 180 or less, At 60 MPH it cools right down to 160. (manual gauge with bulb in manifold) I have a six blade flex fan and no shroud. BTW, whatÆs the deal with the Mexican 4.6? Is it like a stroked 258 or something else?

Try placing a white rag on the end of the taipipe,feel for wetness,maybe even smell it.Just a thought

Ok JF42
Now you have said something!
How it works is like this. When water gets hot it expands and goes into the overflow bottle. Then when cooling the water in the catch bottle will return to the engine and radiator...
Now if when hot the water in the catch bottle overflows and boiles... you have here a problem. MOST likely you have a cracked head. There is prolly a 15% chance (my opinion) you have a leaking head gasket.
So what is it? Is it normal expansion and contraction of the liquid? OR is it abmormal and being forced out by the compression leaking into the water jacket.
A possible check is to pull the plugs and look for RUST on one of them..
If you are truly loseing water in the manner described you have a problem.. no matter how good the engine runs.
Big Jim

I humbly dissagree BigJim. In my opinion, if it were one or the other, that is, crack or gasket, I'd put the odds at 50/50. Still if I were going to bet on it, I'd go with gasket, simply because I've seen far more leaking gaskets than cracked heads. IF there were signs of water in cylinders, still 50/50. Several times I have seen head gaskets that leaked compression/combustion gasses into the cooling system without any such signs. jeepfun4u2, it's not unusual to have a one-way leak. The gasket or crack may only leak when the cylinder is actually firing with no loss of compression until then. so the engine would run normally (except for the temp fluctuations and percolation effects) with no sign of water in cyls or exahust.

Howdy Jeepete
You don't need to be humble about it. I agree with everything you say, except the %. My experience has led me to think the odds waaay favor a cracked head. I admit most of the experience with compression getting to the fluid jacket has been with Chevy's and not with the little six.
Except for the small dissagreement with the odds you have nailed compression leaks.. congrads.
Big Jim <img src="/forums/images/graemlins/kewl.gif" alt="" />

okay big jim....i think that you've convinced me. you're further explanation of the pressure leaking into the water jacket really sounds plausible. is there a sure-fire test for this. can i pressure check the cooling system, and if the pressure is off the chart.....well, there you go! i guess that i've been in denial. thanks again for all the help.

The Mexican 4.6 has a reworked head, that much I know. The spark plugs are the small diameter type, not your average 4.2 type, and if you don't use a thin walled socket, you can't get the wrench in there at all....a tight fit! as far as the crank and pistons, I'm a bit curious myself. The Mexican market has traditionally focused on straight sixes, as gasoline is pretty expensive here, especially if realize that the price of gas is so far out of proportion with the daily wage. Though the six is no penny pincher, it fares better than the 360 V8. This motor was designed to be put in the heavy early eighties Waggies which were and still are(you see them here as commonly as a Wrangler in the states) very, very popular. The motor is a real beast, and with it punched out a couple of thousandths, you've almost got a 5.0 liter on your hands that is a real torque monster. Added benefit....all of the outboard stuff from the 4.2 bolts on directly....no mods! Come on down and pick one up for about $50.00 USD! I found some stats to further answer the bore/stroke question. Enjoy, Rob

Here is some AMC 6 Cylinder engine data from Frank Swygert - FARNA@worldnet.att.net and Andrew Hay - adh@an.bradford.ma.us

AMC six cylinder dimensions in order of size:

SIZE YEARS BORExSTROKE
INCHES (liters) INCHES



195.6 (3.2L) 1955-65 3.125x4.250
199 (3.3L) 1965-70 3.75x3.00
232 (3.8L) 1965-79 3.75x3.50
244 (4.0L) 1987-present 3.90x3.41
252 (4.1L) Mexican Only 3.92x3.41
258 (4.2L) 1971-1995(?) 3.75x3.90
282 (4.6l) Mexican Only 3.92x3.90
293 (4.8l) Jeep Racing 4.00x3.90

okay, i was writing while you two, jim, pete, were posting. I can truly say that i really appreciate you guys, and others....personalizing my dilemma. so, tell me, when I pull the head, what should i look for? what is the operation to detect a crack that may not be evident to the naked eye? thanks again, rob.

When you pull the head, Look closely for cracks. Use a magnifing glass if you have one. between valve seats and sparkplug holes is a common trouble spot. You need a good straight edge and feeler gauge to check for warpage. if it's the gasket leaking that's most likely the cause. There are specs and procedures in the overhaul section of most manuals. The only way I know to check for cracks not visible is magnafluxing. I really don't know much about it except any good automotive machine shop can do it. They can also check for warpage and shave it if necessary. Another common cause of leaking head gaskets is faulty installation. Before you pull the head, put a torque wrench on a few head bolts and check for tightness. If they weren't tightened properly, that could be the cause of your problems. Sounds like the 4.6 is basicly the same as the 258. On the 258 and 232 The first head bolt from the front, on the drivers side goes into the water jacket and is supposed to have sealer applied to the threads on assembly. Probably has nothing to do with it but any one putting on a head with out a book most likely wouldn't realize the hole even goes into the jacket so wouldn't add the sealer. whup, gotta go, good luck.