Engine heating issues and ideas

[sansabarJ]

I'm working on my. 72 J4000 360 engine temp creep up on freeway . Doing 55 or 65mph the temp Creeps up real slow to 195 200 ish . Get off freeway and my temp comes down super quickly with No issues . So we here have covered many reasons and ideas on this subject enough to drive us all nuts . I am going to now install a later Wagoneer airdam . I've not read of anyone looking into the air dam for highway temp creep up resolution results . The air dam would be the place it would be effective on freeway directing air up into front of radiator . Going to give this a real world test .
Many discussions of turbulence and so forth at higher road speeds , so I will put this on and report back on any success or lack thereof. Temp does not creep up on cooler 60 degree temp days on highway. It has to be like 78 to 90 degrees of outdoor temps to have the issues. Yes , ALL issues of block clean out , including core p,in removal and rod clean out of Block, no debris no blockage was found . Engine is pretty new rebuilt with 8000 miles on it. Full fan shroud original Jeep part Not open on bottom 7blade fan and heavy duty clutch , fan on right direction and pulls a ton of heat of new 3 row BJs copper radiator . Sealed radiator on top, sides and bottom with foam rubber seals . Not any trouble with AC on on hot days on street or traffic at all . Just great . Only the highway creep . Better in overdrive as RPM is alot lower . However it should do fine in drive .
NOW , this leads me to talk about these V8S and their tendency to have combustion gasses work their way from lower block deck combustion chambers into the bottom deck coolant passages .
If most don't know , the AMCV8s do not have head bolts that would clamp the cylinder heads
Along these leak prone areas at center bottom of cylinder bores . The solution so far is surface your heads and ALWAYS USE COPPERCOAT SEALER on The metal side of the head gasket. Copper coat really works and seals the deck and head gasket . FELPRO NOW recommends this practice . It did not in the past years ago . The head gaskets are odd in this design of metal only on the one side . I'm not as familiar with Cometic Corteco or Victor on their AMC gaskets . I DO know the slight seepage of combustion gas plagues AMC s with odd overheating troubles and can be difficult to diagnose . A block check fluid test is best . You MUST drain out all coolant with the Block test fluid to not contaminate the fluid and have a faulty test . Only water . I suspect many members may have this issue with head gaskets and this design flaw of not enough head bolts . If you look At the block or head you can see the wide distance of bolts between coolant holes.
I believe BULLTEAR has the aluminum heads to ADD 4 smaller threaded bolt holes to these blocks in the problem area I'm talking about . I had a 401 that would creep up temps on the trail . It WAS leaking on only a couple passages on bottom of the Block deck . Copper coat then was used on the steel side of head gasket liberally . Reassembled and completely resolved heat issue .I did not have anymore heating trouble or temperature creep . So is this your issue ? Possible . Seems alot of temp problems that are nearly not fixable . Also note that on a newly rebuilt engine , it also can have these temps from unsealed head gasket prior to installation. Information provided is from 40 plus years in the engine rebuilding and head gasket service on AMC engine and a great many other brands of engines in the auto truck repair industry . So I've never read any threads on any forums so far regarding this AMC engine issue . This does not apply to Gen 1 287 and 327 V8s.

Hope this can help you all out

SansabarJ

[letank]

could I suggest ... too much advance timing if running on ported vac... run manifold vacuum advance!

[tgreese]

401s are different from the 304 and 360 regarding heating. The 401 bore spacing approaches the limits of the block geometry, and the block casting cannot be reliably over-bored more than 20 thou? Something. A virgin block should be fine, but maybe not a rebuilt engine. Overheating 401s are usually blamed on hot spots in the bore resulting from thin cylinder walls. I mention this because the OP mentions a 401 that exhibited overheating, and I would first try a sonic test of that block before I went on to other more obscure (?) reasons that the OP mentions. Blocks with core shift that results in thin spots can be sleeved to repair. I have never heard of this combustion gas leakage issue, but that does not mean it is wrong or could not exist.

Suggest if anyone suspects this effect in their engines, they do some in-depth online and offline research to confirm these findings. If BullTear is offering the modified heads, there should be plenty of discussion of the design rationale on the Bull Tear site.

[fulsizjeep]

I am a firm believer in keeping the cooling system as stock as possible on the AMC V8s. Fan shroud is a key component. Flex fans, junk them. Fan clutch, use one. Don't be afraid to replace them (this is often overlooked). Thermostat, use a 195* one. Electric fans, overkill and potentially obscures the real problem and a PITA to mess with. Cold air intake from behind the grill to air cleaner. I've been running a 401 .030" bore (407 cu in) since 2004 and overheating has only been an issue once. I should have put a new fan clutch on when I installed the engine but kept the one off the 360. That was a mistake. I can reliably say an open element air cleaner can be a factor in vapor locking.

[tgreese]

I would also mention that you should be able to detect combustion gases in the coolant. There are kits that test for this issue. Usually it's a cracked block or head that is the culprit, or a blown head gasket.

[1978J10REDWHITE]

What do the plug look like?
Perhaps a little richening the jets size up some .
My Pontiacs were always known for the blade in the pump housing were not efficient due to the space behind impeller that with the gap then worked and closed to 0.030” clearances, that made a big difference in water movement thru it and cooled it 25-35 degrees all around.
I wonder if cavitation on the impellers is the issue or and blades are somehow not sufficient to cause adequate flow pumping.
Lastly, what is the age of your radiator??
Definite would get a new one as these old OEM pieces absolutely are not efficient being 45+ years old, no way!

[candymancan]

My 90 gets warmer on th3 interstate than in the city.. you sure this isnt normal ? I mean the engine at 55,65 mph is running at 2500rpm depending on gearing what not at least for my jeep.

And at 35-45 im way lower.. barely at 2k. My 90 gets to about 205 almost 210 or so on the interstate.