I have a 1998 Grand Cherokee 2 wheel drive with a 6 cylinder L 4.0. It has 188,000 miles and the upper rear freeze plug on the head is leaking. I just bought the Jeep a few weeks ago so I do not know any history on the maintenance, or lack of it. Here is my question. Would it be better to pull the motor to replace all the freeze plugs or remove the head and replace all except for the lower rear one at the transmission and the cam plug? I am not seeing any issues (yet) with the head gasket so I'm thinking about leaving it alone...

 

If you're asking my opinion, if you can get to it without removing the head, I would only replace the leaking one. If you get another leaker, then you can do a major refit. JMHO.

 

Yea I thought of that too, but I will have to do the head or the whole engine to reach this one. I will have complete access to the ones on the side either way. I guess my biggest question is should I leave the head alone or not. Thanks for your thoughts...

 

Oh. I wasn't aware there was one on the back of the head. That sucks. If you can somehow get the old one out, they make plugs that tighten up with a wrench, although there isn't much room back there. Dropping the rear crossmember won't be much of a help either. If you should do that, watch out for the radiator hoses cracking the tanks.

 

You will need to pull the head to fix it. Sure, you could pull the whole motor...if you were to do that, replace them all. Make sure to use brass plugs and not steel.

 

On my XJ I replaced the center freeze plug on back of block (coolant).
All three plugs were accessible by removing the transmission.

 

My experience is, if one leaks, the rest are about to go. If your gonna keep the vehicle, i'd advise pulling the engine and replacing all of them. I've only had to address this issue once on a GM V8 that had less than 100,000 miles on it. One started weeping and I tried to treat it with a stop leak product. It didn't work. Within 6 months coolant was pouring out of some others. They were paper thin and rusted through in spots. There was piles of gunk and sediment in the engine that we flushed out. It ran noticeably cooler afterwards. We changed the thermostat and water pump also. One of the drawbacks of buying a used vehicle, even with one that has the legendary "bullet proof" reputation. You never know how well it was maintained before you got it.

 

That's true, replace them all. On the 4.0 I6 motor it looked to me that of the three plugs on rear of block, only the center one retains coolant. The other coolant plugs are under the manifolds.

 

Basically exactly what happened on my XJ. Previous owner had no idea how to maintain it, put stop leak in and it did more damage.

 

Sounds like the best thing is to pull the motor and replace them all. I can get them all that way. Thanks to all...

 

A rubber freeze plug will not stay in place on the back of the head. There is a "boss" inside for a valve stem that prevents the plug from fully seating in place.

I blew 3 of them out before finally pulling the engine and rebuilding the whole thing in my '92 XJ 4.0.

 

I've always heard to stay away from them. I have a set of brass plugs on order. Thanks for the info.

 

Those rubber expansion plugs are designed for temporary use. I'd use one if it was needed in a location that I could easily see and get to. I'd keep an eye on it and replace it occasionally before heavy use or a long trip. I re-did mine with steel. Copper will last potentially forever, however they are more difficult to install since copper is relatively soft. I'd pressure test the engine before I put it back in to make sure I put those in correctly and there are no leakers.

 

Pressure testing the system before putting it all back together is sound advice. However, it does not account for the expansion and contraction experienced with a hot engine. My rule of thumb would be this...if you can tap the new plugs in with ease, you're likely to blow one. That's what happened with mine. The brass ones took a lot more effort to hammer into the block, but I haven't had an issue since (about 2k miles in after the repair).

 

They're brass, not copper.