Picked up a '93 explorewr XLT, auto, 4.0L v-6 for my wife the other day. It only has 92,000 miles and appeared to be extremely well-kept. Runs great, by the way.
After driving it a few hundred miles the cooling system began acting up. It would peg the temp guage now and then, but only for a second or two. When that happened the heater would only produce cold air, and it would go hot again when the temp dropped. I replaced the thermostat, temp sending unit, lower hose, and completely flushed the system, and carefully "burped" any air out of it. At that time I noticed that the freeze plug at the back of the passenger-side cylinder head and been popped-out and a rubber compression/expansion plug is now in it's place (holding fine and not leaking at all).

Sitting in front of the shop I ran it to operating temp tonight...everything was great...drove two miles down the road and the heater started producing cold air, the temp guage was at "M" in the "normal" range, and about that time, POOF-- the freeze plug on the block near the starter blew out. Obviously my cooling system is building pressure in the extreme?
There is NO oil in the water/coolant, and NO water/coolant in the oil. On the other hand, when the engine was warming up there seemed to be a lot of water vapor in the exhaust (the usual white dissipating clouds of exhaust, but more than I might expect on some rigs).
I'm fearing a cracked head or blown head gasket. BUT again, the fluids are not cross-contaminated and the thing runs absolutely great. None of the earlier symptoms where consistant either.

I'd sure like some outside input before I start tearing things apart. We need the rig and can't afford to go looking for another just now.

Thanks much,
Rob

 

When this happens, are any of the hoses collapsing? I suggest pressure testing the system. Obviously, you need to get the freeze plug back in. Is it the expandable type with the bolt in the middle? Also, consider replacing the radiator cap as you may have a pressure related problem.

 

I am assuming that this is a 4.0 SOHC engine. I am currently wrestling a similar problem with a SOHC 4.0 in a 94 Explorer that is one of our shop vehicles.

It was diagnosed by someone else as having a leaking thermostat housing and timing cover. I just signed on here to do some research and see if the timing cover indeed carries coolant and what it will take to reseal it.

In the course of this I resealed the thermostat housing which was leaking and dribbling along underneath the intake manifold and dripping off the back of the engine. That no longer seems to be a problem, but it is still losing coolant sometimes and others not. It is very unpredictable.

If a search uncovers anything I will post results for you in this thread.

 

hello folks,

Thanks for the input. In response, the hoses are not collapsing. In fact, the lower radiator hose (albeit an older one) blew out a couple of days ago with a six inch split.
MB-this is a "push-rod engine," not the SOHC that you are dealing with, although they are pretty much the same relative to cooling I think.

The freeze plug in the rear of the passenger-side head is the rubber/one-bolt/expansion type. The one I discovered while flushing the system hadn't been fully inserted before tightening. I replaced it and it is solid now with no leaks.
BUT my problem yesterday evening involves a different freeze plug....the one on the engine block behind the starter motor blew out violently after a two mile test drive. The rig has a stock 13 lb. radiator cap....I've observed it functioning normally. No external coolant leaks are evident (except for the 1.5 inch "leak" presently located behind the starter...har har har). Apparently the cap pressure-release can't keep up with the rapid pressure increase and it is looking to escape elsewhere????

One additional tidbit. While I was flushing the other day (three times now), I had an adapter and garden hose stuffed into the radiator neck. After freshwater flushing for 5-10 minutes (via a flush T in the heater core hose), I observed the outflow from the garden hose (I'd put the end in a 5 gallon bucket). The water looked clear and clean by then, BUT I did notice an occasional bubble, or even a stream of small, fizzy bubbles like from a scuba radiator....not constant, mind you, but every ten seconds a few would appear.

So again, considering the fact that I have repeated backflushed (with good flow results), properly replaced the thermostat (after testing it, by the way), temp sender unit, a couple of hoses, etc., I'm wondering if there might be a bad spot in a head gasket that is letting a small amount of compression-pressure into the cooling system without either the coolant or crankcase oil being cross-contaminated? I doubt the cast block is compromised, but a head could be cracked, eh? ....as opposed to a bad head gasket.

Any other possibilities anyone can think of or suggestions? Again, the actually cause of the issue is NOT related to a lack of coolant, poor quality coolant, a non-functional thermostat or fan.

Thanks again,
Rob

 

Pull the spark plugs and see if they're wet. A compression check might also aid in determining if a head gasket has blown.

 

Is this a SOHC engine? If so, I have found them VERY hard to purge the air out of. After flushing draining the system as best you can, fill it and idle it until the thermostat opens then you can put more coolant in. THEN keep removing the radiator cap every time it cools off and topping up the system until you get it filled. Only check and fill every time that the engine has gone to operating temperature and then cooled off again.

There is a check ball bleed hole in the thermostat that helps to a point, but it still takes several times to get it filled. The other alternative is a shop with the aparattus necessary to pull a vacuum on the cooling system and then fill it.

Good luck,

 

Nope...this is a push-rod engine, NOT an SOHC engine.

Regardless, do you think an air bubble could cause a pressure build-up that could override the radiator cap and actually blow a freeze plug out of the block (and earlier burst the lower radiator hose, which I (wrongly?) assumed had violently split open due to age?

Beyond a cracked head or a head gasket beginning to blow, is there anything that could cause this to happen to a cooling system that hats good flow and cross-flow and a functional thermostat? I really don't want to pull the heads, was hoping somebody could convince me otherwise, har har.
thanks

 

i vote bad head gasket.

a compression check should be first on your list.

 

So it's a push rod engine, that is very different. It is definitely time for compression test, and more importantly a leak down test while listening for escaping air and watching for air bubbles in the radiator. If you have a cooling system pressure tester, try that first, since it's quicker and easier. If that doesn't show up anything, THEN move on to the leak down test.

Unfortunately the push rod engines have a history of being prone to blow head gaskets. If the leak down test and other diagnosis lead you to a blown head gasket, pull BOTH heads, do a valve job while they're off, have them pressure tested and surfaced or at least checked for straightness. Don't even THINK about finding the side that is leaking and doing only that side. Do them both! Also, the head bolts are stretch type, so you should use new ones.

The push rod engines have some irritating things you will discover when removing the heads like not being able to access all head bolts unless the exhaust manifolds are removed, but at least you are not doing the same work on the same engine when installed sideways in a Windstar. That one IS irritating.

Best of luck,

 

Yes sir.....that appears likely to be the "winning" vote. Of course, if that's the case my next question will be "why is the gasket blown?"

I can get a brand new set of the aftermarket heads (with beefed-up castings in the areas of known weak points for '90-'94 4.0 litres) for less than four hundred dollars. Even if mine don't have any cracks, I doubt if I can go through them for that much. Does anyone have any opinions on the "improved" aftermarket heads?

I'm off to "un-borrow" my compression gauge from the neighbor.

Thanks much for the input,
Rob

 

Doc,

Thanks for the reply. Unfortunately, we moved recently and I'm not all set up for wrenching yet, at least as far as a leak-down or cooling system pressure check....and being in a small, rural town means dragging the rig quite a distance to do so. I am going to do the compression test, likely do it tonight.

As you mentioned/reccomended in your post, I am planning on doing both sides and replacing all head bolts and gaskets. As far as going through the heads, I was planning on it, but I can get two new aftermarket 4.0L heads (the "improved" ones with heavier castings at know weak points in the stock heads) for well under 4oo bucks. Doubt I can go through my old ones for that, even if they aren't cracked. Do you have an opinion on the aftermarket "improved" heads? Also, do you think it likely that my pushrods are going to need replacement? I've heard that the older 4.0L engines tend to starve the pushrods and rockers for lubricant. Reckon I'll know when I see 'em.

Thanks much,
Rob

 

you are putting the cart before the horse.

find out what is wrong, then buy what you need to fix the problem.

do compression test, than do pressure check on cooling system.

you never mentioned if this was a 4x4 or 4x2.

 

Yup....but when you have to budget ranch expenses down the line a forecast is better than a surprise.

The rig is a '93 XLT 4x4 with a 4 speed AT, 4.0L pushrod engine.

I just re-acquired my compression tester. Beyond that testing will be a bit difficult, since I have two missing freeze plugs (although one has a rubber compression plug in it). And I'm not set-up for either additional test at the moment, much as I would like to be.
We live near a small rural town of a few hundred people....it's a bit problematic logistically to get the vehicle to a dealer, etc. etc....meaning I could spend as much on a tow as I would on a new head for one side, and pay for the other side on the tow back. Be at least 25 miles to the nearest possible shop with the capabilities and more likely almost 60 miles one-way. I'm an A&P (aviation) and fly the birds I work on, so I'm a reasonably capable wrench-buster (never died in one of 'em...yet).

The possibilities appear to be one of three things: 1)a blown head gasket; 2)a cracked/wrecked head; or 3)a crack or problem in the block. This thing is really building up high pressure under a load...but not caused by overheating. At least the comp test will let me know which jugs to look at closely. Considering what it costs for the gaskets and head bolts, I'll be doing a top-end regardless while things are off (unless, of course the problem is in the block). At 94,000 miles it would be foolish not to....so I'm just balancing the varioucosts between ne, remanned, and re-working the ones I have.

 

Check your auto insurance policy. Most will reimburse you for towing expenses up to a limit.

Or, you can join AAA. AAA Plus membership entitles you to four service calls per year, with towing up to 100 miles per call. The membership is something like $130/year. My guess is that a 60 mile tow bill would be way more that that. If you have a standard AAA membership, you can upgrade.

Good luck!

And you get a discount at NAPA with your AAA card.

 

i do have to ask, why do you not go back to the seller, he must have known about this problem.

i hope you did not pay too much for this vehicle.