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Xj 4.0 overheating
- Thread starter Bmfinney
- Start date
Well I’m down to either replacing the radiator which I ran water through it with a water hose and it didn’t seem clogged but idk. Or a cracked head.. I have a misfire now on I think two cylinders can’t remember which ones but believe 2 or 3 had to walk away from it gonna start fresh tomorrow.
Unclewolverine
NAXJA Forum User
- Location
- Kansas
If you have changed everything else then it's the radiator. They easily get clogged up to the point where you can't break the scale loose. No need to try any tricks or anything fancy, a clean stock system will cool a stock xj in any conditions.
- Location
- Minneapolis, MN
Fully describe, explain, and provide details about when the overheating occurs, and what symptoms are observed.
Generic overheating info follows:
Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a worn out mechanical fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller, leaky frost plugs, or even a defective radiator cap. None of the cooling system parts last forever.
The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others, and your engine will overheat. Temperature creep on the 4x4 trails, at idle, or in stop-n-go traffic, points to a weak or failing mechanical fan clutch or worn out water pump fins.
The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles, or every two to three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.
-Inspect all of the frost plugs in the block and the ones on the backside of the head for rust holes and coolant leakage.
-Use a chemical flushing/cleaning solution to remove mineral buildup or rust, flush with clean water, and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a genuine Jeep 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out radiator cap will allow not hold system pressure which can cause boil overs and/or allow the coolant flash over into to steam. You will likely see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
If you have covered all the points listed above and still have overheating issues, inspect and test the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant
Read more about cooling systems here –
http://www.offroaders.com/tech/engine-overheating.htm
http://www.carparts.com/classroom/coolingsystem.htm
Generic overheating info follows:
Overheating can be caused by anything that decreases the cooling system’s ability to absorb, transport, and dissipate heat, such as a low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated mineral deposits in the water jackets or radiator, a defective thermostat that doesn’t open, poor airflow through the radiator, a worn out mechanical fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller, leaky frost plugs, or even a defective radiator cap. None of the cooling system parts last forever.
The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others, and your engine will overheat. Temperature creep on the 4x4 trails, at idle, or in stop-n-go traffic, points to a weak or failing mechanical fan clutch or worn out water pump fins.
The most important maintenance item is to flush and refill the coolant periodically. Coolant should be replaced every 36,000 miles, or every two to three years. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.
-Inspect all of the frost plugs in the block and the ones on the backside of the head for rust holes and coolant leakage.
-Use a chemical flushing/cleaning solution to remove mineral buildup or rust, flush with clean water, and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a genuine Jeep 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out radiator cap will allow not hold system pressure which can cause boil overs and/or allow the coolant flash over into to steam. You will likely see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
If you have covered all the points listed above and still have overheating issues, inspect and test the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant
Read more about cooling systems here –
http://www.offroaders.com/tech/engine-overheating.htm
http://www.carparts.com/classroom/coolingsystem.htm
RCP Phx
NAXJA Forum User
- Location
- Phoenix,Az
Everything Tim stated is right on. Unfortunately you didn't say what year XJ you have and what brand of parts you been using. You very possibly will be returning to this thread with the same results after the new radiator is in!
Unclewolverine
NAXJA Forum User
- Location
- Kansas
Doubt it. 99% of xj over heating issues are either the thermostat or the radiator.
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
Replace the fan clutch. They cause more problems than anything else. Go with one from a GC for max cooling.
Unclewolverine
NAXJA Forum User
- Location
- Kansas
Fam clutch does make a difference along with a fan shroud if it is missing. The fan should be very loud and noticeable when it starts getting warm.
Thanks for the reply’s guys much appreciated. Is there anyway to see if the fan clutch isn’t working? When it was running I stuck a stick in it and it acted like it was engaged? I ended up tearing it down again gonna take the head to a machine shop and see if the head is warped I didn’t machine it I just stuck a new gasket on it and bolted it together that might have been the problem.
- Location
- Houston, Tx
What year is your Jeep?
Unclewolverine
NAXJA Forum User
- Location
- Kansas
Nobody thought to ask if this was 0331 head year? To be fair he never did say he was losing coolant.
Some comments on cracked heads;
1. Years ago there was a company that had a reputation for their cracked car heads, and I had one.
2. All the cracks started around the hot exhaust valves.
3. I studied my cracked head and concluded the head exhaust ports were intentionally designed to raise exhaust gas temperatures to reduce emissions.
4. I picked up a used identical head and ported/opened-up all the exhaust runners and installed slightly larger exhaust valves to increase exhaust gas flow.
5. Put it all together and ran the car forever without ever cracking another of these problem cracking heads.
Best regards,
CJR
1. Years ago there was a company that had a reputation for their cracked car heads, and I had one.
2. All the cracks started around the hot exhaust valves.
3. I studied my cracked head and concluded the head exhaust ports were intentionally designed to raise exhaust gas temperatures to reduce emissions.
4. I picked up a used identical head and ported/opened-up all the exhaust runners and installed slightly larger exhaust valves to increase exhaust gas flow.
5. Put it all together and ran the car forever without ever cracking another of these problem cracking heads.
Best regards,
CJR
- Location
- Houston, Tx
You should pass on a 0331 head unless it has TUPY stamped on it. If it does not, it is prone to cracking.