I blew the head gasket on my 87 last month pushing it down I-90 for 450 miles on 31" tires and stock gears (not to worry, 4.9-1's are going in day after tomorrow), so this past weekend I replaced the head gasket, heater core, and heater valve (heater valve cuz the old one was seized, and core because I wasn't getting hot air anymore...turned out to just be leaves but since I had the new core what the hey). Precision straight-edged the gasket surfaces of the head and block six ways from Sunday looking for warpage in excess of the 0.002" limit, and couldn't even begin to fit a 0.001" feeler under it, so the head's good. Additionally, I replaced the thermostat and the temp sender, just in case the old one was telling lies. Also I looked down into the water jacket and couldn't see any signs of crud plugging it up down in the engine.

Still overheated...so after some collective head-scratching with a friend who's a Samurai guru, we figured water pump since the fluid didn't seem to be circulating. Got a new pump and replaced it, but there was nothing wrong with the old pump and the rig still overheats with the new one.

So finally today I put a new radiator cap on with no luck, then replaced the entire radiator with a new one, no luck. With the thermostat out I can flush water freely through the system with no sign of blockage or crud coming out, and I boiled the thermostat and it works as advertised.

Has anybody ever had this sort of issue, or have any idea as to what the heck is going on here? I'm completely stumped. I think I have literally replaced everything of significance in the system. I am considering the possibility that the guage is lying to me, so I'm going to get a generic one from auto zone so as to verify the dash guage, which goes to full-on, all-the-way hot even though the engine feels like it's just normal operating temp. It doesn't smoke the residual oil from my weepy camshaft cover off like it should if it were legitimatly getting holy smokes hot, but I don't want to assume that and blow my new head gasket.

Sorry for the long post! I'm just completely miffed at this point...

Ed

Replace the clutch fan and all the hoses. There not only the only parts left to replace, but probably the culprit all along.
 A collapsed lower hose will stop all watter movement. Fire up the rig and watch the lower hose. If bad it will collapse when the thermostat opens...
 A bad clutch fan will prevent all air movement.....Boxcar...
 

Common Problem/Oh Oh/Mistake !!!

DID YOU INSTALL THE HEAD GASKET ON BACKWARDS/UPSIDE DOWN?!!!
IF YOU DO, A WATER PASSAGE IS BLOCKED OFF THAT WILL CAUSE THIS PROBLEM !!
FIX IT NOW BEFORE YOU RUIN YOUR ENGINE !!

I know it's alot of "ReWork" but I bet that's your problem,

CAPT

Common Problem/Oh Oh/Mistake !!!

DID YOU INSTALL THE HEAD GASKET ON BACKWARDS/UPSIDE DOWN?!!!
IF YOU DO, A WATER PASSAGE IS BLOCKED OFF THAT WILL CAUSE THIS PROBLEM !!
FIX IT NOW BEFORE YOU RUIN YOUR ENGINE !!

I know it's alot of "ReWork" but I bet that's your problem,

CAPT

Thought about that, but I installed the head gasket the same way the old one had been installed. There was no "top" marked on the new gasket, so I put it in with all the markings up (P/N and what not). I noticed that there are only two ports that were affected when I test fitted the new gasket. With the gasket upside down the forward hole would be partly blocked and the rear would be exposed, and right side up the front would be open and the rear partly blocked. All the long narrow and little triangular ports around the cylinders are clear, those two round ones were the only ones that seemed to be affected. I double checked how the old one sat and it also partly blocked the rear round hole. Should I have taken a exacto knife to the head gasket to open that rear hole up the rest of the way? I thought about it but figured that would be a bad idea to hack on the gasket considering the old one was identical and the engine ran fine with it ever since I've had the rig, right up until the gasket blew.

Thanks for the help! This was my first head gasket swap so I very well could have bungled something up like that.

+1 on mechanical gauge and verify the problem.

Sounds silly but my tow rig got sidelined for overheating a couple years ago and it was a defective rad cap!!!good luck

My money is on the clutch fan i had one go bad and it would go into the red i caught it before the gasket blew

Common Problem/Oh Oh/Mistake !!!

DID YOU INSTALL THE HEAD GASKET ON BACKWARDS/UPSIDE DOWN?!!!
IF YOU DO, A WATER PASSAGE IS BLOCKED OFF THAT WILL CAUSE THIS PROBLEM !!
FIX IT NOW BEFORE YOU RUIN YOUR ENGINE !!

I know it's alot of "ReWork" but I bet that's your problem,

CAPT

You are so wrong.  If the headgasket is put on wrong, it blocks an oil passage, not a water passage.  The oil passage that is blocked is the one that feeds oil to the top of the head.  It usually doesn't take long to sieze the cam and ruin the head.

mr_ed....the headgasket is not causing your overheating problem, so don't worry about it.

So does the gauge instantly go to full hot, or does it take a few minutes?  How long exactly?  
If you turn the key on and don't start the engine, will the gauge go to full hot?

Does it overheat when driving down the highway?  If so, then I would rule out the fan clutch....since at highway speeds there would be enough air moving through the radiator that it would cool fine, even if the fan clutch is not operating properly.

So SORRY,
For BEING SOOOOO WRONG,

Tried to Help,

Continue On!!

CAPT

I couldn't see all of your post, did you replace the thermostat?