Any caveats before I pull the heads...

[niceguy]

I am contemplating pulling the heads on my '94 4.0L OHV engine to resolve a cooling issue.

The truck overheated on my wife three weeks ago (on a trip to the bank to pay it off - ain't life ironic...) due to a stuck t'stat. She drove it very hot, so I fear the worst (blown head gasket or cracked head(s)). I've replaced the t'stat, upper and lower rad. hoses, radiator cap, and pulled the radiator to check it out; it was very clean, so I just put it back in the truck.

Symptoms are as follows: Pumps coolant out of radiator into overflow tank, filling it every 60-70 miles. "Check Engine" light comes on intermittently; generally is ON when under light cruising load, and OFF when loading the engine (uphill, etc.). No sign of coolant in oil, or out the exhaust. If I start the engine with the cap off and coolant level topped off, I get an initial geyser of coolant out of the cap. This seems odd to me. I replaced plugs and wires one week after the mishap and checked for signs of coolant on plugs; there was none. This morning the engine ran VERY rough for the first 30 seconds, then smoothed out. Truck runs great except I have to pull over every 60 miles and drain the overflow tank and dump it back in the radiator.

Motor has about 105K miles on it.

Before I bust my knuckles, thought I'd check and see if any of you have been down this road and have any tips/tricks/warnings/advice for me. Any easy way to verify my suspicions before I tear it apart? Any tricks to identifying possible internal cracks? Any other parts to replace while I'm in there (valve seals...)? Must I have a valve job done, or can I get away with just lapping the valves real good? Any good overhaul manuals for the 4.0 besides the Haynes book? Any other input from anyone that's actually done this job?

TIA,
Michael

 

[SteveVB]

Michael
Some questions, and thoughts...
Is it still getting hot when the coolant flows out? If its not, then it sounds like the cap may be not working or the wrong application if you just replaced it. May still have air in the system, open the heater valve and let the coolant circulate.
Do a pressure test of the system before you pull the heads. Also check/replace the overflow to rad hose it may be kinked or clogged.

Check the oil- any coolant? Level change? May want to check the intake manifold bolts the heat may have loosened them.

Last thing- when you replaced the t-stat was the bleed hole on top? T- stat facing the right direction?

Pulling the heads isnt hard just takes time to get to them.
Valve job who knows, if the seats look ok and not too much slop on the stems then maybe ok to lapp, then again you have them off so the extra cost of having the valves done wont be much- especially after you factor in all of the time it takes to get the heads on and off. If you do a valve job get new springs since youve got more than 100k on the engine.

Hope that helps some.

 

[niceguy]

answers and questions

Hi Steve - I usually drive it until the temp gauge starts to creep up, then I know it's time. I replaced the cap with a gennie Ford part from the dealer and it looked identical to the one I replaced. Spring seems a little firmer though.

I've tried running the engine with the cap off until the t'stat opens to make sure I've bled out all of the air, then top off the radiator and close it up. Makes no difference.

I'm unplugging the overflow hose from the rad. to drain the tank when it gets full, and it flows well, so doubt that's a problem.

Don't have a pressure test rig of my own. Are these available for the DIYers at a reasonable price, or should I just take it to the shop and pay The Dealer?

No signs of any goopy stuff on the dipstick although I'm gonna change the oil soon and see what comes out. Level doesn't change. Good idea about the intake bolts - I'll check 'em and torque 'em if they're loose and see if the problem goes away.

When I replaced the t'stat I know I put it in "inside in/outside out", but don't recall how I oriented the bleed hole. I remember looking at it and checking the book and the t'stat package for instructions, but found nothing. I think I put it in with the bleed at 3 o'clock or 9 o'clock. Would this cause my coolant to pump out into the overflow tank?!?!? If so, then shame on all parties for not detailing the importance of this.

And lastly: I'm not familiar with the 4.0L. If I do a complete overhaul of the top end, what are the odds of me aggravating any weaknesses on the bottom end? I've done valve jobs on old high-mileage small-block Chevies, only to have the rings let go a few months later due to increased compression. What's the longevity of the 4.0L piston ring seal, etc. like?

Thanks again,
Michael

 

[SteveVB]

Michael

Could be the engine still has air in it. The air bleed has to be at 12 o clock. Its not on the package(as I remember) but the two manuals that I have (Haynes- multi year, and my FSM) specifically state straight up or 12 oclock. This may be a cause of air in the engine. Much easier to redo the t stat than pull the heads! Lets hope that could be it!

I think I got a pressure tester for 20 bucks or so from Sears a few years ago, so should be avail fo less than a hour of a dealers time. If a rental shop is nearby that may be a good bet- cant imagine it could cost more than 20 a day. Some of the big chains and parts houses around here rent tools for free- have to pay a deposit equal to the cost but its refunded upon return.

I have done a couple top end rebuilds of various engines with no probs. Havent done the 4.0 (rebuilt the whole thing). I think as long as you keep coolant out of the cylinders you should be ok, drain the block before you pull the heads so the coolant doesnt get into the cylinders.
The fact remains that the cylindrs will have 100k plus miles on them and the heads in effect new. My block with 160k and low oil pressure (clogged pick up)had a good ridge but did not burn, or use oil between changes. Compression was to specs. Valve guides needed to be replaced on a few cylinders though.

Good luck.

 

[niceguy]

"Much easier to redo the t stat than pull the heads! Lets hope that could be it!"

Absolutely! I'll take care of that tonight or Wednesday. I'll also track down a pressure tester.

Thanks again...

 

[flyguy]

Errr.. when you put a stat in it has to be rotated a certain way? Doh! I just stuck mine in there. Working okay so far. Is there anything I should look out for to make sure its in right? I sure would hate to have to dig in there just to find out its in right.

nick

 

[AaronE19]

Michael-
assuming it's not just a 'stat install problem, I'd think about a motor rebuild as opposed to just valvetrain work (well, FIRST I'd think about nailing down the problem with a high degree of certainty before investing any money in 'fixing what ain't broke'... we all know what frustration that can hold). I lost my intake and exhaust valves on the #5 cyl over the winter, looked into replacing/rebuilding the heads, but ran into the same concerns that you voiced about blowing piston rings under higher compression. I took my query to a couple trusted mechanic friends who both said: "why put a band-aid on a turd?." gotta love mechanic humor... in all seriousness, valve work is not as inexpensive as it used to be (unfortunately), and it didn't make sense to tear her apart and replace the head only to have to tear her apart again a month down the road because I put a connecting rod thru the cylinder wall and across the street. I sincerely hope it's only a thermostat the 4.0L is really a pretty reliable motor (as in, when I lost a cylinder it STILL didn't leave me stranded on the roadside), but anything with 100k+ miles on it is going to have significant wear already. it's impossible to tell, so you might as well be safe. case in point: I was getting a little oil blow-by about 4 months before my motor went, so I took it in for a compression test. 5 of 6 cylinders tested out at spec, right on the nose. the 6th was I think only 1lb under spec and that wasn't the cylinder that gave out in the end. (it's enough to drive you mad, I know)

Aaron

 

[niceguy]

update...

Well, I did some more poking around Wednesday night. Pulled the plugs to read 'em, etc. Porcelain in the front plugs on each bank were slightly discolored (remember I changed 'em 2-3 weeks ago), while all the others were very new/white. Some slight moisture on the threads of a few of the plugs, but it smells like fuel/oil, not coolant.

Did a compression test, and all looked good (160-170PSI), so doesn't look like a head gasket.

Pulled the t'stat and rotated it so that bleed valve was at 12 o'clock. (Was around 4 or 5 o'clock. Ooops.) SteveVB was right - it's covered in the manual. I just ought to read more thoroughly.

Took the truck to the dealer last night and asked them to:
1) do a pressure leak-down test on the cooling system
2) test the coolant for the presence of CO or fuel
3) read the Check Engine codes for me and interpret

Hope to hear from them late today. If not by then, then it will probably be Monday. Hopin' for sooner instead of later... Will let you know what I find out and keep you posted.

Thanks for your help guys.

 

[niceguy]

Well, bad news and worse news.

Picked up the truck late Friday and the service advisor said that the test for CO in the coolant came back VERY positive, so a blown head gasket or cracked head was the most likely culprit. (So tell me something I DON'T know...)

Saturday I tore the top end of the motor, then on Sunday I took the heads to a machine shop to be tanked and magnafluxed. They called me on Monday morning to report one head warped .007, and the other head is cracked. At lunch I ran to Cylinder Head Exchange to buy a remanufactured head. Dealer wanted $300 for a bare head, $423 for a complete head. I paid $175 for the reman. unit, with 90-day warranty. The other head is getting a valve job and I'll pick it up today and start putting everything back together tonight.

Cylinders looked good. Very little ridge, and can even see some honing cross-hatch, which is surprising for 105K miles.

I'm just going to do the top-end, and hope the bottom-end holds together. If not, guess I'll be doing this all over again soon.

PS. SteveVB was right about the intake manifold bolts, too. They were barely finger tight!

 

[kilroy]

Get new head bolts!

I believe Ford is still using torque to yeild head bolts on most OHV engines. Just to be on the safe side I would replace the head bolts. Theres nothing worse than getting to the last torque setting on the last bolt and having it snap. ( It happened to me on one of my 5.0 engines) DOH

 

[niceguy]

already got 'em

Thanks for the reminder, but I already got 'em. Many of the newer motors (not just Fords) are using the TTY bolts nowadays. And it seems almost impossible to miss that on this application. I've seen notices in the Haynes manual, on the gasket set box, the machine shop guys told me, the other machine shop guy I talked to.... I think I even saw a note about it on the AutoZone receipt when I bought the gasket set. The only one that _hasn't_ told me about it yet is my wife. Wonder what she's waiting for? ;-)

Michael

 

[flyguy]

Hey guys, I was reading the in manual about when puttin on the head bolts they have to have so much torque on them.. Im gussing thats what you guys are talking about... well.. how do you know? do you need a special tool to do that? Where can I get it and how much? Hmmm

Nick

 

[niceguy]

The Haynes manual has torque specs (sequence and torque) in the specifications area of Ch. 1 or Ch. 2. I don't recall the exact numbers or details off hand, but it's something like this: the heads are torqued to 40-something ft-pounds, then you torque the intake manifold to 30-something inch-pounds, then you torque the heads to 80-something ft-pounds, then torque the intake again, then tighten the head bolts an additional 80-85 degrees.

Torque wrenches range in price from $25 to $100, depending on type, size, features, etc. Check out http://www.sears.com, go to their Tools section, and do a search on 'torque wrench'. You'll get a bunch of impact wrenches and other junk, but page down and you'll come to a list of torque wrenches. This will give you some idea of what you're looking at...

Michael

 

[Chav]

Man those stupid head bolts. They killed me. Took forever to torque em to 40 ft/lbs and I thought I was done, but noooo. Anyway Good luck!

-Chav

 

[flyguy]

I was looking at the wrenches... they have a short handle and a long handle. It would be easer to get the torque with the longer one.. but is there clearence? Opinions???

Nick

 

[kilroy]

$25 to $100? I wish

I was a mechanic for 5 years, so guess what kind of tools I needed! Snap-On! My small torque wrench cost about $150, and my larger one $275! Of course they are guaranteed accurate for 1 year, and can be recalibrated for $10 for another year.

I forgot about that damn degree wheel you need to torque those heads.

 

[flyguy]

Yeesh! Thats expensive. I have the choice between one for 69 bucks or a digital one for 100.. then the long short thingie...

Nick

 

[niceguy]

degree wheel? WHAT degree wheel?

Well, I bolted up the heads and intake last night. Actually, I spent almost as much time CLEANING the lower intake manifold as I did putting the heads on. Bolting it all up was a BEAST of a job. Wasn't too bad until I got to the last step. How the $*@#&~!& do you measure 80-85 degrees IN the engine bay? Would probably be easy on an engine stand but IN the truck is another matter. And the back left bolt on the passenger side, up against the heater box - forget it! What were those engineers thinking? Chipped a couple of teeth off of the torx bit trying to get enough oommph on it. And can I get some sympathy for the bruises and busted knuckles? Don't have a degree wheel attachement for my wrench so I had to eyeball it. A couple of the bolts I couldn't get enough leverage or wiggle-room to "eyeball" 80-85 degrees, so I targeted 120 ft/lbs, which is what 80-85 degrees appeared to amount to.

As for $275 for a big torque wrench: if I was using it every day in my work, I wouldn't blink at the price. I've used cheap beam-type torque wrenches before (sheesh), and now I've got me a "click" wrench, which I really like. For as little as I use it, it's perfect. And I figure it's a great size for beating the engineer that decided that would be a nice place for the heater box, and his associate who decided that 80-85 degrees was a good way to measure bolt-stretch. Now if I could just figure out how to get it on that back bolt...

 

[flyguy]

Haha.. so I take It I should go for the smaller wrench? I was thinking about it.. its gunna be hard getting to all those bolts. Changing spark plugs on that thing takes days!

Nick

 

[niceguy]

All Done!

Well, I'm about 99.9% done with it! Spent several hours Monday wrapping up most of it. Then last night my neighbor came over to help me put the hood back on and sort out some vacuum line connection confusion. Fired it up and took it for about a 15 minute test drive and all is well except for that blasted Check Engine light. The truck runs great, temps are stable, the recovery reservoir gurgling is gone, and all seems right in my little world. I drove it to work today just to make sure that my wife doesn't get any surprises - it ran fine for the 25 mile trip in.

Guess I'll take to the dealer to have the Check Engine light diagnosed, unless one of you guys can clue me in to how you read those things.

Thanks again for everyone's collective help. The list has been a great resource!