1998 4.0 V6 139,000 miles

Wondering if I could get some thoughts/insights on my issue. I received this truck from a family friend. It was running just fine until about a month ago. With the engine cold, when I crank it I instantly get pressure in the radiator. No smoke from the exhaust, no residue on the spark plugs (they are brand new), no milkshake in the oil and there is not any coolant on the ground. Everything I have looked up points to head gasket but I would like to see if anyone has had similar issues. If you have what is the ball park cost to repair it and would it be worth it to do so. I am sorry if this is a repeat question.

Thanks in advance.

 

Welcome to the forum

Do the Glove Test then you will know for sure and you can find out which cylinder has the leak
The 1990-2000 4.0l OHV engine did have a weak spot between valve seats, so would crack there and leak pressure into cooling system

Cold engine
Unplug 4 wire connector on Coil Pack, you want a No Start
Remove rad cap
Remove overflow hose
Plug the overflow hose port with a vacuum cap, should be one on the engine you can use, or use putty or gum to plug it
Its better if coolant level is down an inch or so from the top, if not you can drain some out, lower is fine

Put a latex glove on rad cap opening, seal it in place with rubber band, or you can use a balloon or even a condom instead

Cooling system is now sealed
Crank engine and watch the glove

If glove starts to bounce you have a leak from a cylinder into cooling system, you are seeing the Compression stroke's 150psi
Remove 1 spark plug at a time and crank the engine
When glove stops bouncing the last spark plug removed was from the leaking cylinder
Put it back in, just hand tight, to confirm

You can have more than one leaking cylinder, so you will see glove bounce LESS but still bounce, so continue removing spark plugs

If glove doesn't bounce/inflate then something else is wrong, not a head gasket or cracked head issue


Long shot:
If you put on a Fan belt incorrectly it can spin the water pump in Reverse, so instead of PULLING coolant IN from lower rad hose, it will PUSH coolant OUT into lower rad hose, and since thermostat on upper rad hose is closed it will PUSH coolant up and out of rad cap opening, its not really "pressure" its just flow