I recently acquired a Dak QC at a very good price from a dealership. It was advertised as having a blown head gasket, but I've been looking for a 4DR 4WD for a few months and this one was a deal I couldn't pass up. It has 131k on the meter.

I have been a mechanic / technician for 20+ years, both automotive and aircraft. I've done head gasket jobs on many models, and worked as a certified Dodge mech many years ago (although not on these newer 4.7s, looks like nice engineering on it). So I figured this one should be a cinch.

At the dealer, truck starts great...glass smooth idle and rev. Took it on a short drive and she promptly gets hot. Not overheated, but went from cold to 3/4 on the gauge in two blocks. She's hissing and dripping when we get back. So it's towed home. On initial inspection, coolant is low obviously. On closer insp, filler neck is cracked in upper hose and there looks to be some sort of block seal junk coming out. Replaced neck and flushed system a lot (flushed rad and engine separately, then together with Prestone flush). Put on OBD2 scanner to watch temps. Thermostat is removed. Gets to ~230 on coolant temp sensor, 5/8 on gauge. Loosened cap to check for bubbles and it blows like a geyser. Cooled, filled and put a 13# safety cap on it and repeated. Changed out fan 'cause it was barely turning at idle. Temps about the same...not really overheating. Checked radiator and several places around engine and found nothing over ~190 there, but lifting the safety release it boils in the overflow for quite a while.

Deciding not to risk a complete overheat of the aluminum heads, i pull them off. To my dismay, no gaskets blown. Engine inside looks like it has 5000 miles on it. No sludge in fill neck, milky oil, carbon in fill neck and valve covers is very low, plugs are clean, water pump impeller is attached and no bad bearings, no washed cyls...in fact, they all look clean and even.

Did I just take apart a perfectly fine motor? The original rad cap is rated at 20#, and never overflowed. The safety cap at 13# never blew until I lifted the lever....but it boils out all the water. I'm going to plane the heads, put in the usual gasket set, change the water pump, replace a timing guide I cracked (timing set looks alright). I had to change the exhaust manifolds (terribly rusted, northern car), and just that justifies the disassembly, but the getting hot issue bugs me.

Any insights?

Thanks!

 

When you put the engine back together put a new coolant temp sensor in it and check the wiring for the sensor.

 

@mountainmanmike,

Why would that be? Are coolant temp sensors a problem with these motors? Is the wiring an issue? I get no CEL and OBD2 isn't reading anything for codes. Not understanding why you would go that direction.