Engine Woes...

[Brandon Nootenboom]

Well, I my 4.0 either has a blown head gasket or god forbid a cracked head... I'm hoping this weekend to get a chance to positively I.D. the leak point. It's an external leak, not enough to cause overheating but you can smell it outside the truck and see it dripping down the engine. I know it's not the intake or a freeze plug, I'm guessing and hoping that it is only going to be a head gasket since I wasn't having drivability issues when I parked it over a month ago. I just had a couple questions if it ends up being a cracked head.

1) Could I just replace the bad head and have the other one machined or should I replace both? (Their around $600/head for new)

2) Could I get good used head(s), have them machined and throw them on

3) At 260,000 miles would it be worth trying to find a lower mileage or newer 4.0? Even tough the engines been well maintained? I'm paranoid about fixing the top end then losing the bottom end...

Any advice would be greatly appreciated!

 

[doorgunner]

Lots of extra cash.?..............go for the Gold!

No extra cash.?..............fix only what is broken/if you're gonna keep the vehicle---fix it with quality parts

 

[Andy D]

Slow down. I wouldn't do anything until the leak was located. It maybe a hose or something. If it is an external leak chances are very good it isnt head related. Even if it is a bad gasket , it may respond well to a 1/2 dose of Bars leak sealer. I wouldnt be in a huge rush to do a head R+R on a 260k mile engine

 

[RonD]

I did my '94 4.0 heads a while back.

It was $110 each to have the heads cleaned, surfaced and pressure tested, they also put in the valve seals I provided.
Besides the head gasket kit, you will need a set of head bolts, as these are "stretch" bolts so can not be reused.

These heads usually crack between the valve seats so you would see it in the cooling system not as an external leak.
The 15psi pressure in the cooling system couldn't blow a head gasket, the 150+psi in a cylinder can blow a head gasket and it could show as an external coolant leak on the head but it would also shown up in the cooling system.

You can do a Balloon test if the cooling system is still intact.
On cold engine
Remove rad cap.
remove overflow tube.
Start engine
Place balloon, or latex glove or sandwich bag over rad cap opening, pinch tightly to seal, place finger over overflow outlet.
If it starts to inflate you got a blown head gasket...or cracked head.
There is no pressure in the cooling system until coolant gets to above 100degF.

If you do have a cracked head then you only replace that 1 head not both.

From provided info I am thinking intake leak, I had one of those leaks.

Machine shops can sometimes get better deals on new or rebuilt heads so good place to start if a cracked head is found in the pressure test.
A used head is also an option but it needs to be cleaned, surfaced and pressure tested as well so weigh that cost + used head, against a new/rebuilt head.

Unless you are having lower end problems a used engine would, IMO, be a big gamble.

A couple of my exhaust manifold bolts were too rusted to remove, don't strip the heads, if you run into this remove the exhaust pipe and pull the head with exhaust manifold attached, easier to work on then, if you still can't get the bolts off a muffler or machine shop can, cost me $20 to get 4 bolts out, took local muffler shop about 15 min., I spent 2 hours trying.

 

[DFracing]

Define "drivability issues"

Also there are a few things it could be start by checking the valve covers get a flashlight and check up and down where it's coming from.

 

[DFracing]

.

If you do have a cracked head then you only replace that 1 head not both.

Only do 1 head on a engine that has 260k? That's like buying 1 new shoe because your other one got a hole in it. If your going to go through the trouble of replacing a bad head, replace both

 

[RonD]

Only do 1 head on a engine that has 260k? That's like buying 1 new shoe because your other one got a hole in it. If your going to go through the trouble of replacing a bad head, replace both

I think you are misunderstanding the process.
Both heads are removed and pressure tested, if one has a crack then that one is replaced.
Heads do not "wear-out", they can crack from a casting flaw and/or over heating but they don't wear-out, and a head that doesn't crack after being overheated is a keeper, no casting flaws, it has been tested.
Nothing like the shoe comparison, but yes if I could find a matching shoe I would just replace that 1 shoe, that would make the most sense, it is just a shoe, easy to swap, and I could get another when the "good one" wears out.


And at 260k there would be two schools of thought, cheapest fix possible to get another 60k-100k out of the low-end, drive-train and suspension, because at some point without a restoration the rest of the vehicle will deteriorate past economic viability.
Or pull the engine and do a complete rebuild, because you will be keeping it and restoring it as needed.

 

[Andy D]

There you go, scaring me again. The 4.0 in the Rat runs pissah. History is unknown, could a head crack out of nowhere? Over heating , I can see, but just happening?

 

[RonD]

There you go, scaring me again. The 4.0 in the Rat runs pissah. History is unknown, could a head crack out of nowhere? Over heating , I can see, but just happening?

No, never heard of a spontaneous crack, maybe in a new engine it could happened, i.e. factory defect.
Not sure if mis-installation of rocker studs, exhaust/intake bolts or head bolts could crack a head, but I wouldn't think so.
Pre-ignition(ping/knock) or running lean can cause higher temps in the cylinders, but it would show up on the temp gauge.

But "history unknown" could mean someone put "stop leak" of some kind in it before you got it, that stuff can last months or fail in a few minutes, depends on the leak.