About a week ago my Zuk ran hot.  I checked and there was no antifreeze in the overflow.  I let it cool down and drove it to the parts store where to my surprise the radiator and overflow were full and it did not run hot.  I then drove it to work and when I arrived it was running hot again.  This time after it cooled the radiator appeared bone dry so I filled it up.  I parked it and checked it out this past weekend to find the radiator looked bone dry but after starting the Zuk the radiator actually started to fill up as the truck warmed up.  I changed the Thermostat again, different brand since I have only had the old one for a few months and it runs lower than normal.  Today I noticed the coolant coming out of the overflow, could be I overfilled it this past weekend.  It ran normal this morning but after about 40 miles the coolant was gone and the temp gauge went to High

Is it normal for the radiator to "fill up" as the truck warms up?  I removed the radiator cap and squeezed the upper hose and I feel coolant flowing through and it squirts up where the cap is supposed to be so the water pump is probably working.

No "milkshake" in the oil so that's a plus, however, there could be a hairline crack in the head gasket that allows the coolant to "steam" and thus lose all the coolant

no leaks on the ground or the engine compartment that I have seen

Any thoughts?

Thinking of replacing the cap even though it isn't leaking maybe it isn't holding the pressure and is letting all the coolant go to the reservoir and out the overflow tube

Anyone agree or have a suggestion?

Wouldn't not holding the pressure be defined as leaking?

Yes - if the system is consistently filling the overflow reservoir, replacing the cap is a cheap & easy first step.

If it's losing coolant, the coolant is going somewhere. If you can't find an external leak, I'd have to say you have a head gasket problem. The cap, if it's bad wouldn't cause the radiator to go dry, even if it wasn't holding any pressure it would only let pressure equalize, not suck the system dry.
Sorry to say but it sounds like head gasket to me.

I have seen bad caps allow water to be bled into the overflow but not back in.  It's an easy thing to replace, I would give it a shot first.

Starting to blow out white smoke so it looks like Head gasket


Anyone know of a good shop in the Southern California area?


Anyone have any experience with Head Gasket Sealer - like Dura-Seal or something?  I'm weary of fix in a can but 1200 to 1500 for a head gasket is rough

I suggest fixing the headgasket right.  Don't put miracle fix-it crap in your engine.
A headgasket isn't really hard to do yourself.  It can be done with the engine in the samurai.
It sounds like you overheated it a few times, so there is a good possibility you warped the head.  So I would have it checked, and decked if necessary.

Anyone have a recommended book to change a head gasket?

The FSM is a good reference.
You should be able to find a copy at either acksfaq.com or suzukiinfo.com