Jeep 4.0L Engine Blown Head Gasket – Symptoms & Complete Guide


All images within the guide are from my 1998 Jeep Wrangler sport 5.0 5 speed, which I sold to my dad. Awesome to have a jeepin family.

Jeep over the years is known for making a quality, and reliable engine.  While they leave you wanting in the power and torque numbers, they will always get you home. From the trails to the highway, I am comfortable taking my Jeep anywhere.  

Reliability aside, Jeep from the 1940s to late 2006 focused on a machine tailored to one specific niche; Off-road. A machine designed to conquer countries and win wars. So it’s no wonder they didn’t put a governor in a Jeep,  it will govern itself. Unsure steering, clunking gears, putter-like engine output, loud highway driving. 

If you dare go fast, it’s just not gonna last. Heh… 

From curb jumping at your local mall to rolling down a hill. The Jeep will get back up swinging, but check your head gasket when you get home. 

Symptoms of a blown head gasket: 

  • Engine overheating 
  • Oil in coolant 
  • Coolant in oil 
  • White exhaust smoke 
  • Milky oil 
  • Weird smell 
  • Loss of engine power 
  • Boiling/bubbling coolant in radiator 
  • Coolant loss without a leak 

Testing for blown head gasket: 

  • When the engine/coolant is cold – turn the engine on. If coolant on top of the radiator is bubbling, it may have a blown head gasket. 
  • White smoke when idling, after the engine has warmed up completely.  
    • Note: white smoke on start up is okay. That is just condensation bubbling off white in the exist pipe. 
  • Pull oil dipstick out, If coolant looks milky. You may have a blown head gasket. 
    • If oil is milky, drain oil from the pan. If the oil is milky, or has coolant separated from the oil. You have a blown head gasket. 
  • Check the coolant degas bottle, if the coolant has oil in it, or has coolant and oil separated. You have a blown head gasket. 
  • When accelerating, a plume of white smoke comes out of the exhaust, and the engine bogs down. You may have a blown head gasket. 
  • Buy a head gasket test kit from an auto parts store. This will connect to the radiator fill or cap. 
    • Follow the instructions, it will pressurize your crank case.  If the pressure goes down, you may have a blown head gasket. 

Can a blown head gasket hurt my engine? 

Yes, a blown head gasket could cause major damage to an engine.  It is important to fix a blown head gasket as soon as possible. Coolant in the oil can break down the oil quickly… which will leave your engine completely un-lubricated. 

Blown head gasket engine damage list: 

  • Piston damage 
  • Hydrolocked engine 
  • Cylinder wall damage 
  • Cylinder engine head damage 
    • Valve damage
    • Cracked heads 
    • Valve guide damage 
  • Camshaft damage
  • Bearing damage 
  • Crankshaft damage 

Can I wait to fix my head gasket? 

Unfortunately, the longer an engine has a blown head gasket, the more damage it will cause. 

I know this is not what you want to hear, but it’s the truth. Head gasket repair can be extremely expensive. Here are my recommendations to just get by

Tips to get with a blown head gasket 

  • Change oil every 50-100 miles 
  • Keep coolant reservoir topped off at all times 
  • Keep an eye on your coolant temperature gauge; never let it get over manufacturer’s recommendations. 
  • Do not accelerate quickly 
  • Drive the speed limit 

These ideas are not a sure bet to keep your engine safe.  These could all leave you on the side of the road with a blown-up engine. Honestly, sometimes we have to do what we gotta do. 

How much will a head gasket repair cost? 

A head gasket repair will cost between $500-$3000 depending on if you go to a shop or do it yourself.  For a Jeep 4.0l or 2.5l engine, a head gasket repair will cost between $500-$2500 depending on if you go to a shop or do it yourself.  

The total job cost was $829.88 (DIY).  

I could have done this project for much less! But being OCD,  I wanted to replace everything I could on the way out. 

How long does a head gasket repair take? 

The base time for labor. (First-time head gasket repair in a Jeep). Total labor was 22 hours. This does not include the time it took at the machine shop.  

I pulled the head off in about 12 hours, the cylinder head spent 6 days at the machine shop. Then it took 11 hours to assemble everything again.  

You should allow 30 hours of labor to this project.  If you choose to buy a new cylinder head. You could potentially do this project over a single weekend.  

I have a friend who completed this in about 8-15 hours. Really depends on experience!

If you are completely certain the cylinder head is not damaged.  You could potentially neither send the head to a machine shop or buy a new head. You must be certain there is no damage. 

I did not want to take this risk.  

Things to consider replacing while replacing your head gasket: 

Here are the items I replaced on the way out when I changed my head gasket.  I will separate this list by “required” and “not required” 

Required head gasket repair parts: 

  • Cylinder head bolts 
  • Valve cover gasket 
  • Thermostats housing gasket 
  • Head gasket 
  • Exhaust manifold gasket 
  • Intake manifold gasket 

Not required head gasket repair parts: 

  • Valve springs 
  • Push rods 
  • Injectors 
  • Lifters 
  • Engine accessory’s belt 
  • spark plugs

Why do I need to replace cylinder head bolts when changing a head gasket? 

The head bolt threads stretch when torqued to spec. This is by design.  It is required to replace head bolts when changing a head gasket.

Why should I replace pushrods? 

As long as your pushrods are kept separated from exactly where they came from, and paired with the rocker they went with; unless damaged. Pushed rods do not need to be replaced.  

If you just cannot bother with keeping them untouched by any kids or pets from the time the head is removed to the time it comes back from the machine shop. Just plan to buy new pushrods and lifters.  They are inexpensive! 

Why do I need to replace injectors when doing head gaskets? 

You do not have to.  I did not replace my injectors, instead, while the head was at the machine shop I sent the injectors to a local shop to be spray tested and thoroughly cleaned.  I noticed big improvements in drivability, I assume they were quite dirty. 

Why do I need to replace the engine accessory belt? 

You do not have to, but since the belt is already off. Just take it up to the auto parts store and have them match it. Better safe than sorry. 

Why do I need to replace spark plugs when doing head gaskets?

Many times, spark plugs will be fouled or damaged from coolant leaking into the cylinder from a broken head gasket. While these spark plugs may still work, it is always a great idea to replace them while it is easy.

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