This Jeep hates me


Jakebrake

Member
Joined
Oct 7, 2020
Messages
33
Location
Philly burbs
ok. the old motor was replaced with a rebuilt 4.2 liter, year unknown. this engine was rebuilt years ago, by an unknown shop. (i know...bad idea. was the only one we could find). replaced water pump, thermostat, and radiator. around town, runs fine. i took it out on the open road, and, presto! overheat city...to the point that the plastic (i know...another bad thing) radiator blew to kingdom come. towed back to the shop, replace thermostat, nd, radiator, and, she purrs like a kitten. idles smooth, behaves fine.

is there anything particularly quirky about 4.2 engines i need to know? this jeep was only doing 52 when all hell broke loose. i'm sort of scratching my head, and, so is my mechanic.
 

machoheadgames

Certified YJ Researcher
Supporting Member
Joined
May 19, 2020
Messages
302
Location
Dallas, TX
No, nothing special about a 4.2. Very basic cooling system. Possibilities are that wrong coolant was mixed and caused sludge, improper direction water pump was installed and didn’t pump water correctly, system was driven immediately after being worked on and didn’t have time to bleed itself, etc. No telling what exactly happened but they aren’t a flawed design and in good condition, have no inherent issues.

Also nothing wrong with a “plastic” radiator. Like metal, there are many types of plastic. Radiators are made of a special type of composite meant to last in the application. Hell, most YJ and TJ radiators last at least 10 years, if not 15, 20, or even more. My OE radiator went to 22 years and it wasn’t the composite that failed.
 
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Chris

Administrator
Staff Member
Joined
Sep 28, 2015
Messages
29,795
Location
Salem, Oregon
X2 to what he said.

Some people like to assume the plastic portions of radiators and cooling systems are bad. That plastic is used for OE applications and is anything but bad. It's designed to last well over 10 years, and in many cases can last over 20 years. I know tons of TJs that are still on their factory radiators after 23 years!

I also don't believe there is anything inherently "quirky" about the 4.2 either. I think a lot of it just comes down to how well they are maintained, like any engine.
 
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cas

Member
Joined
Nov 11, 2020
Messages
26
Location
NY
I had an S-10 Blazer that started over heating one cool night out of the blue. It would be fine for a while, then over heat again. Over time I flushed it, purged it and changed the antifreeze several times. Changed the thermostat several times, changed all the hoses, changed the water pump, changed the radiator, changed the fan clutch, pulled the cat and the muffler, tested for head gasket leaks, checked timing. All of this over the course of an 11 month period. Nothing solved the problem. And then one day it just went away and never did it again. Drove it several more years without issue. Who the #@^* knows. lol
 

smgager

Member
Joined
Dec 16, 2020
Messages
38
Location
Wilmington, NC
Make sure to check your fan clutch is working as well. I had overheating issues that I could not track down that turned out to be the fan clutch.