BLOWN HEAD GASKET

[Broosedamoose]

So the other day while driving on the highway I blew a head gasket. The engine temp shot up so fast that the small heater hose going from the t-stat housing to the hard line blew apart. Since I have to pull the heads off to replace the gaskets is there anything else I should do or look for? The engine got pretty hot before I could pull over! I'm pretty sure I will have the decks milled to be certain they are flat but I'm wondering if there other things to do while the heads are off?

 

[RonD]

Well there is a cause and effect order here
Head gasket don't just "blow" out of the blue, especially the 4.0l SOHC heads, head gaskets blow BECAUSE of overheating the engine, the head metal expands too much and crushes the head gasket's metal ring around a cylinder.

If you haven't disassembled the cooling system yet you could repair the hose and then put a cooling system pressure gauge on rad cap, pump pressure up to 20psi, disable spark, and then crank engine over(you don't need coolant in the engine for this test)
If pressure jumps up and down then yes you have a blown cylinder gasket
You could remove 1 spark plug at a time and crank engine
When gauge stops jumping last spark plug removed was from the blown cylinder, if jumping just gets less then you have more than 1 cylinder leaking so continue removing spark plugs


But to answer the question, yes have the heads pressure tested and replace the valve guide seals(the heat killed them)

 

[Ramcharger90]

Depending on how much coolant got into the oil the bearings could be next.....

 

[Ejay]

I bought one with what was thought to be overheating due to head gaskets, turned out to be cracked heads, each side had a small crack between the valves closest to the firewall. It was an OHV rather than SOHC thank goodness. Bought new heads , been fine since.
Good luck
Ej

 

[RonD]

You would have to run the engine for a while with coolant in the oil to cause bearing damage
The issue with coolant in the oil is because unlike oil the coolant will boil and vaporize above 213deg so washes off bearings
Oil temp usually runs at 210-230deg and there in lies the problem, but again you would need to run engine a few days with a high mix of coolant to cause bearing damage, IMO
It doesn't "hurt" the bearings just promotes more wear if it washes enough oil off the bearings as it circulates


4.0l OHV had weak spots in its casting between valves in the heads so when over heated they would crack there, 4.0l SOHC was different casting so didn't have that issue
Any head can crack if metal gets hot enough, so heads should always be pressure tested if replacing a head gasket.

 

[Ramcharger90]

Chicken or egg.... Gotta drain that oil and see how much mixed. Did it over heat from a slow leak or a sudden failure? It's something to consider. Not saying its the cause or will happen but ive seen it happen. Within a month of a head job. Could have been a bad mechanic or a unrecognized failure.

 

[Otis413]

I'm rebuilding a 4L SOHC right now (I just came in for lunch) it overheated bad, (failed water pump,) and the owner kept pushing it trying to get to work. I assumed it was a blown head gasket, after pulling both heads I can't pin down an exact problem spot. There was antifreeze coming out the exhaust but none in the oil, found antifreeze pooled in #4 cylinder, even tho they look ok (?) I think I'm going to replace the heads...

Anyway, even if it looks good replace the water pump while you have it apart.

EDIT: Just found my straight edge, (Steel carpenters square) both heads are warped, I can fit a 0.015 feeler gauge under the straight edge (measured end to end, centered) on the PS head and 0.019 on the DS head, I'm not sure what the limit is on these alum heads but I'm sure that's a bit much...

 

[adsm08]

I'm not sure what the limit is on these alum heads but I'm sure that's a bit much...

If you can see light under the straight edge it's too much.

 

[Broosedamoose]

It did over heat about a year ago when the thermostat for the fan died. I would think if that was the cause the gasket would have blown sooner. I had the heads milled, valve seals replaced and changed the oil. Everything seems to be ok now.

 

[Broosedamoose]

Well, I take that back. Everything is not fine. The engine seems to idle rough. Almost like it has a cam. While sitting in traffic it seems to want to lurch forward sometimes. Is it possible he got the timing wrong when he reinstalled the cams on the heads? I think it would be a lot more noticeable if that were the case but I'm not positive. Any ideas?

 

[Broosedamoose]

Still trying to figure this out. The engine stalls almost every time I put the truck into reverse! The idle is very rough. When the electric fan cuts on the engine RPM's drop and it almost stalls! Checked everywhere for a vacuum leak but can't find anything. It runs as if there was a vacuum leak or the MAF sensor was unplugged. Haven't done a smoke test yet but I think that's next. I'm wondering if the intake warped when it overheated. I've put in new spark plugs and wires so I know that's not the problem. Yes, they are on in the right order. Already checked that. Anyone got any other ideas to look for?

 

[RonD]

I know its a pain but I would do a compression test first
All spark plugs removed for good cranking speed
cold engine
charged battery, 12.3volts to 12.8volts
Test each cylinder

If compression numbers are all above 160psi then not a cam timing error, 4.0l SOHC runs 9.7:1 compression ratio so should be closer to 175psi static

Compression test first because if that is the issue then you will just be wasting time and money on spark and fuel when it won't help

 

[Broosedamoose]

Ok, thanks. I'll have him do the compression test and if it's all good, then I'll have him do the smoke test.

 

[Eddo Rogue]

I seized the engine on my dirt bike because of a coolant leak....now I feel less bad about, so thanks for that. Good luck bub.

 

[Broosedamoose]

Did the compression test today and he got around 140 psi on all six cylinders. So, he thinks the timing is not set right. He's going to borrow the timing tool from Ford and check it next week.