2000 4.0 - blown head gasket
#1
2000 4.0 - blown head gasket
Hey guys,
I was driving home a couple days ago and noticed the temp gauge creeping up. I cranked up the heat on full blast to try to help cool things off but noticed fairly quickly that the air began blowing outside temp, so I knew there was a severe coolant loss. By this time I was only a few hundred yards from home so I kept going and parked it. First thing I checked was the oil dip stick as I recalled having a blown head gasket in my old S-10 years ago, and sure enough, I had that tan coffee colored oil, so it clearly leaked in vs. out. In fact, I couldn't find any evidence of coolant leaking OUT at all. I pulled off the valve covers last night and the oil and coolant mix coated those with sludge. There was still a fair amount of coolant that poured out when pulled the lower radiator hose. I'll continue tearing things down over the next couple days as time permits (and also realized I didn't have the right tool for the head bolts), but my question is this: I know there is a possibility the heads are cracked or warped. I'm fine with having to replace those if needed, but I'm wondering more about whether the coolant mixing with the oil in the way that it did could have caused more damage and what I would need to do to address that, or if it is even worth it at all? This truck was a bit of a cherry and only had 58,000 miles on it when I bought it off an old guy in October 2018. It now only has 62,000. Body and frame is perfect so I'm hoping she can be saved without having to drop a new engine in it if it can be avoided.
Thanks!
I was driving home a couple days ago and noticed the temp gauge creeping up. I cranked up the heat on full blast to try to help cool things off but noticed fairly quickly that the air began blowing outside temp, so I knew there was a severe coolant loss. By this time I was only a few hundred yards from home so I kept going and parked it. First thing I checked was the oil dip stick as I recalled having a blown head gasket in my old S-10 years ago, and sure enough, I had that tan coffee colored oil, so it clearly leaked in vs. out. In fact, I couldn't find any evidence of coolant leaking OUT at all. I pulled off the valve covers last night and the oil and coolant mix coated those with sludge. There was still a fair amount of coolant that poured out when pulled the lower radiator hose. I'll continue tearing things down over the next couple days as time permits (and also realized I didn't have the right tool for the head bolts), but my question is this: I know there is a possibility the heads are cracked or warped. I'm fine with having to replace those if needed, but I'm wondering more about whether the coolant mixing with the oil in the way that it did could have caused more damage and what I would need to do to address that, or if it is even worth it at all? This truck was a bit of a cherry and only had 58,000 miles on it when I bought it off an old guy in October 2018. It now only has 62,000. Body and frame is perfect so I'm hoping she can be saved without having to drop a new engine in it if it can be avoided.
Thanks!
#2
RF Veteran
iTrader: (1)
Very rare now a days for blown head gasket to cause coolant/water in the oil, it can happen but in the 4.0l is usually intake gasket issue.
No, you should be fine if you only ran it a few hours with coolant oil mix.
The point of using oil is to cool the bearings and coolant does the same thing, but.............coolant can boil away above 230deg and oil won't, so coolant doesn't work well in crankcase/bearing applications
If you left it a long time, say a year, you could get some rusting on the bearings, but if you drain oil, fix the crossover point, in the next month or two it will be fine
Use a less expensive oil like straight 30w and cheap filter for first startup after the repair, run that for a week then do another oil change with your preferred oil and filter
Machine shop can vacuum test head for cracks($50), and resurface if no cracks are found, no need for a valve job on the 4.0l OHV heads under 250k miles
Just for future reference, when you think you have a failed head gasket or cracked head, on any engine, do the Glove Test, FIRST, that will tell you if there is a cylinder leak to cooling system AND it will tell you the exact cylinder or cylinders that are leaking, so you can ID the leak after disassembly
No, you should be fine if you only ran it a few hours with coolant oil mix.
The point of using oil is to cool the bearings and coolant does the same thing, but.............coolant can boil away above 230deg and oil won't, so coolant doesn't work well in crankcase/bearing applications
If you left it a long time, say a year, you could get some rusting on the bearings, but if you drain oil, fix the crossover point, in the next month or two it will be fine
Use a less expensive oil like straight 30w and cheap filter for first startup after the repair, run that for a week then do another oil change with your preferred oil and filter
Machine shop can vacuum test head for cracks($50), and resurface if no cracks are found, no need for a valve job on the 4.0l OHV heads under 250k miles
Just for future reference, when you think you have a failed head gasket or cracked head, on any engine, do the Glove Test, FIRST, that will tell you if there is a cylinder leak to cooling system AND it will tell you the exact cylinder or cylinders that are leaking, so you can ID the leak after disassembly
Last edited by RonD; 05-13-2019 at 09:14 AM.
#3
Thanks RonD - I think you're right. I just went out and took a closer look and there's definitely coolant in the intake manifold so I'm going to hope that's all it is. I really don't want to tear it down much further beyond that, but will see what happens as I get in to it further.
Is this a common failure on these engines, or is it likely because the truck was driven rarely by the previous owner and then I began running it as a daily driver? I was expecting some leaks here and there from all the sitting it had done.
Is this a common failure on these engines, or is it likely because the truck was driven rarely by the previous owner and then I began running it as a daily driver? I was expecting some leaks here and there from all the sitting it had done.
#4
RF Veteran
iTrader: (1)
The 4.0l OHV uses cast iron heads and an aluminum intake manifold.
Coolant passes thru the intake manifold at the front, where thermostat is, from one head to the other, and to the heater core
If coolant isn't changed every 2 or 3 years then this flow of coolant can cause galvanic corrosion of the aluminum and the gasket because of the difference in the two metal types.
So coolant can start leaking out of the front corners of the intake where it meets the heads, or inside to the oil gallery under the intake manifold.
You should see the corrosion on the intake and on the gasket if this happened.
When a head gasket blows or head cracks some of the 1,000psi pressure, in a cylinder when it fires, with be pushed it to the cooling passages, this causes air to be forced in with it, actually exhaust, lol.
This air displaces the coolant in the head, and causes higher pressure in the cooling system
Cooling system has a radiator cap rated at 14 or 16psi, so this higher pressure will push open the rad cap and send coolant over to the overflow tank, causing it to fill up,
this loss of coolant and the air in the heads causes the over heating.
Low coolant, from a leak, also causes overheating, and overheating causes it own high pressure, but because coolant was low the overflow tank will just bubble not fill up because there was no coolant at the top of the radiator
So there are differences to look for when diagnosing over heating issues.
The Glove Test uses the 150psi cranking compression from each cylinder to determine if one or more of the cylinders are leaking pressure into the cooling system, for future reference always do this simple and FREE test before disassembly and anytime you have an over heating issue in any vehicle
Coolant passes thru the intake manifold at the front, where thermostat is, from one head to the other, and to the heater core
If coolant isn't changed every 2 or 3 years then this flow of coolant can cause galvanic corrosion of the aluminum and the gasket because of the difference in the two metal types.
So coolant can start leaking out of the front corners of the intake where it meets the heads, or inside to the oil gallery under the intake manifold.
You should see the corrosion on the intake and on the gasket if this happened.
When a head gasket blows or head cracks some of the 1,000psi pressure, in a cylinder when it fires, with be pushed it to the cooling passages, this causes air to be forced in with it, actually exhaust, lol.
This air displaces the coolant in the head, and causes higher pressure in the cooling system
Cooling system has a radiator cap rated at 14 or 16psi, so this higher pressure will push open the rad cap and send coolant over to the overflow tank, causing it to fill up,
this loss of coolant and the air in the heads causes the over heating.
Low coolant, from a leak, also causes overheating, and overheating causes it own high pressure, but because coolant was low the overflow tank will just bubble not fill up because there was no coolant at the top of the radiator
So there are differences to look for when diagnosing over heating issues.
The Glove Test uses the 150psi cranking compression from each cylinder to determine if one or more of the cylinders are leaking pressure into the cooling system, for future reference always do this simple and FREE test before disassembly and anytime you have an over heating issue in any vehicle
Last edited by RonD; 05-13-2019 at 10:46 AM.
#5
I just got the lower intake off... I'm still not 100% confident about whether I should just take my chances by replacing the intake gaskets, or if I need to remove the head and change the head gaskets. It looks like there is evidence of some leaking at the back of the lower intake, but I think what may have happened is that the 6 lower intake bolts were actually somehow loose? I was expecting to have to give some force to back those off but they practically spun out by hand. Only one had to be started with a good tug on the ratchet. A quick google makes it sound like this may be common with the 4.0 OHV. Think I'm safe assuming that's it, putting new intake gaskets in, and not bothering with the heads?
Also, I did some reflection... I've always driven the truck gently since I got it, but about 15 minutes before this all happened I did push it to the limit trying to merge quickly on the highway... not something I'd typically do but because of some construction at that ramp, it's quite easy to be an idiot and accidentally cut people off as you enter the highway, which I did and so stomped on the gas to get myself out of the way. Wondering if I did this to myself now LOL
Also, I did some reflection... I've always driven the truck gently since I got it, but about 15 minutes before this all happened I did push it to the limit trying to merge quickly on the highway... not something I'd typically do but because of some construction at that ramp, it's quite easy to be an idiot and accidentally cut people off as you enter the highway, which I did and so stomped on the gas to get myself out of the way. Wondering if I did this to myself now LOL
#6
RF Veteran
iTrader: (1)
Common issue on the 4.0l OHV were lower intake bolts getting loose, they only have 15ft/lb torque, which is just snug, you should use Locktite on these bolts threads when reinstalling
This would cause check engine light to come on and set Lean codes, but rarely leaked coolant, it could for sure, just not as common as Lean codes
You could still do a test by sealing up the cooling system
Assuming water pump is on
Lower radiator hose is on radiator
And spark plugs are still in place
Put rad cap on
Seal upper rad hose opening on the radiator, i.e. use plastic bag with rubber band, bag needs to be tight
Seal open heater hose that was on lower intake, big bolt or another plastic bag
Now there should only be 4 openings left, 2 on each head, front and back
Toilet paper................yes, lol, tape a sheet of toilet paper so it hangs down over coolant opening in the head, do all 4
Pull out Fuel Pump Fuse, or Fuel Pump relay, either is in the engine fuse box
Find the Alternator wires, make sure they are taped and can not touch any metal
Hook battery back up, be careful, watch for shorts
Have some one crank engine over while you watch toilet paper, it should just lay there, if one side moves then there is a leak in that side, could be head gasket or cracked head, and it will Pulse the toilet paper
You could remove spark plug at a time on that side and toilet paper will stop pulsing when spark plug is removed from leaking cylinder
This would cause check engine light to come on and set Lean codes, but rarely leaked coolant, it could for sure, just not as common as Lean codes
You could still do a test by sealing up the cooling system
Assuming water pump is on
Lower radiator hose is on radiator
And spark plugs are still in place
Put rad cap on
Seal upper rad hose opening on the radiator, i.e. use plastic bag with rubber band, bag needs to be tight
Seal open heater hose that was on lower intake, big bolt or another plastic bag
Now there should only be 4 openings left, 2 on each head, front and back
Toilet paper................yes, lol, tape a sheet of toilet paper so it hangs down over coolant opening in the head, do all 4
Pull out Fuel Pump Fuse, or Fuel Pump relay, either is in the engine fuse box
Find the Alternator wires, make sure they are taped and can not touch any metal
Hook battery back up, be careful, watch for shorts
Have some one crank engine over while you watch toilet paper, it should just lay there, if one side moves then there is a leak in that side, could be head gasket or cracked head, and it will Pulse the toilet paper
You could remove spark plug at a time on that side and toilet paper will stop pulsing when spark plug is removed from leaking cylinder
#7
Just got the heads off... the head gasket did indeed blow... as far as I am aware this was the one and only time it overheated and the drive was short... contemplating whether I should just get new heads... I’m not particularly concerned about cost. I just don’t want to have to take this thing apart again. What a pain in the butt it was.
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Brad1485 (04-09-2023)
#8
#9
RF Veteran
iTrader: (1)
Overheating will crush a head gasket, even once if it lasts long enough, there is no exact time or temperature , but it can and does happen with only one heat up
4.0l head was also prone to cracking if over heated, at the valve seats, you can usually see it.
All metals expand when heated, the higher the temp the more the expansion
The head gasket is sandwiched between two metal parts.........................
Head gets the hottest since its at the top so expands the most, and if coolant is low...........then no coolant in the head just in the block so head gets super hot and expands ALOT, and crushes the head gasket to block, blown head gasket
The expanding metal can also cause a head to crack at a weak spot
If you want to reuse the heads then have them pressure tested, first, for cracks
4.0l head was also prone to cracking if over heated, at the valve seats, you can usually see it.
All metals expand when heated, the higher the temp the more the expansion
The head gasket is sandwiched between two metal parts.........................
Head gets the hottest since its at the top so expands the most, and if coolant is low...........then no coolant in the head just in the block so head gets super hot and expands ALOT, and crushes the head gasket to block, blown head gasket
The expanding metal can also cause a head to crack at a weak spot
If you want to reuse the heads then have them pressure tested, first, for cracks
#10
Alright - so here's where I'm at with the truck. First, I was lazy and didn't have the heads pressure tested, so feel free to yell at me over that lol. I did use a straight edge and feeler gauge to look signs of warping and didn't find any, and yes, I am aware doing this on my own in my poorly equipped tool shed is not ideal and it is certainly possible (if not entirely likely) that I missed something a professional wouldn't have.
A couple things I did notice while tearing everything down. Valve cover gaskets - awful and leaky - I attribute this to the fact that the truck literally wasn't run for about potentially 5ish years by the previous owner after he fell ill, except for, as I am told, "maybe it took a trip to the dump a few years ago" and to sometimes move it if it was in the way.
Intake gaskets looked "OK", except on the lower intake in the far back there was signs of leaking near the coolant passages. I actually believe this might have been where the real problem began and caused the overheating? After taking the heads off there was some coolant in one of the cylinders and the plug looked a little nasty, and the gasket was clearly leaking. I think it took me nearly a whole afternoon just to get the gasket residue of the block and heads, but I did it carefully and with nothing sharp.
Anyway, skip ahead... engine is back together. It starts, but I instantly got P0122. She does idle quite rough when first started and is prone to stalling. If you give it some gas however and get the RPMs above 2200 for a minute or so and let off the gas it will stay running and drops RPM down to about 1050-1111 according to my OBD scanner, but it does seem to sputter and shake. I have changed out the oil twice because it got pretty nasty right after the blown gasket. After the second change the oil seems pretty clean, though I may replace the oil and filter one more time. no signs at this point that I screwed up installing the gaskets. No coolant leaking as far as I can tell and the oil clean as I said.
So back to the rough running, I will admit I noticed I somehow missed a vacuum line and and as soon as that was corrected that was when it started to actually stay running, but it is still pretty rough but sounds perfectly fine and smooth above 2200 RPM as I said. What else should I be checking?
A couple things I did notice while tearing everything down. Valve cover gaskets - awful and leaky - I attribute this to the fact that the truck literally wasn't run for about potentially 5ish years by the previous owner after he fell ill, except for, as I am told, "maybe it took a trip to the dump a few years ago" and to sometimes move it if it was in the way.
Intake gaskets looked "OK", except on the lower intake in the far back there was signs of leaking near the coolant passages. I actually believe this might have been where the real problem began and caused the overheating? After taking the heads off there was some coolant in one of the cylinders and the plug looked a little nasty, and the gasket was clearly leaking. I think it took me nearly a whole afternoon just to get the gasket residue of the block and heads, but I did it carefully and with nothing sharp.
Anyway, skip ahead... engine is back together. It starts, but I instantly got P0122. She does idle quite rough when first started and is prone to stalling. If you give it some gas however and get the RPMs above 2200 for a minute or so and let off the gas it will stay running and drops RPM down to about 1050-1111 according to my OBD scanner, but it does seem to sputter and shake. I have changed out the oil twice because it got pretty nasty right after the blown gasket. After the second change the oil seems pretty clean, though I may replace the oil and filter one more time. no signs at this point that I screwed up installing the gaskets. No coolant leaking as far as I can tell and the oil clean as I said.
So back to the rough running, I will admit I noticed I somehow missed a vacuum line and and as soon as that was corrected that was when it started to actually stay running, but it is still pretty rough but sounds perfectly fine and smooth above 2200 RPM as I said. What else should I be checking?
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Marlasboy (10-20-2023)
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