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90 4,0 liter going warm.
- Thread starter XJ88NO
- Start date
- Location
- Terra Firma
If your '90 has the original cooling system, you have a plastic bottle mounted on the firewall, on the passenger side above the heater fan. This bottle is a pressure bottle, and the cap for that bottle is, ib fact, the "radiator" cap.
If I understood your message correctly, you replaced the cap ("New top ..."). However, many of our members have discovered that a new cap does not seal when installed on an old bottle. The bottle warps, or cracks, and as a result the new cap cannot keep the system pressurized.
So ... my first suggestion is to replace both the bottle and the cap together.
The other possible problem is air trapped in the system. When you replaced the thermostat, did you use a genuine Jeep thermostat? The genuine Jeep unit has a small bleed hole with check valve in the flange. Here in the USA, none of the aftermarket replacements have this bleed hole. The purpose of the hole is to help remove trapped air from the system when it is first filled after service.
Even with the correct thermostat, it is difficult to remove all the air. Various members use different methods to do this. My method is to run the engine with the cap on, but loose (so it doesn't hold pressure, but so that boiling water cannot spill out). As soon as the coolant boils in the bottle, shut off the engine and wait. After a few minutes (5 to 10 minutes) you will see the level of the coolant in the bottle suddenly begin to go down rapidly. This means the system is cooling off and the liquid is contracting. When this happens, pour in more coolant, to keep the bottle half filled.
When the system stops pulling in coolant, repeat the process. I find that it requires four to six cycles of heat up/cool down/add coolant before the air is purged from the system.
I hope this helps.
If I understood your message correctly, you replaced the cap ("New top ..."). However, many of our members have discovered that a new cap does not seal when installed on an old bottle. The bottle warps, or cracks, and as a result the new cap cannot keep the system pressurized.
So ... my first suggestion is to replace both the bottle and the cap together.
The other possible problem is air trapped in the system. When you replaced the thermostat, did you use a genuine Jeep thermostat? The genuine Jeep unit has a small bleed hole with check valve in the flange. Here in the USA, none of the aftermarket replacements have this bleed hole. The purpose of the hole is to help remove trapped air from the system when it is first filled after service.
Even with the correct thermostat, it is difficult to remove all the air. Various members use different methods to do this. My method is to run the engine with the cap on, but loose (so it doesn't hold pressure, but so that boiling water cannot spill out). As soon as the coolant boils in the bottle, shut off the engine and wait. After a few minutes (5 to 10 minutes) you will see the level of the coolant in the bottle suddenly begin to go down rapidly. This means the system is cooling off and the liquid is contracting. When this happens, pour in more coolant, to keep the bottle half filled.
When the system stops pulling in coolant, repeat the process. I find that it requires four to six cycles of heat up/cool down/add coolant before the air is purged from the system.
I hope this helps.
8Mud
NAXJA Forum User
- Location
- Central Germany
I´ve had trouble before with aftermarket thermostats and the supplied gasket. The Jeep gasket opening is not round, it has a cut out for the heater/surge tank hose coming from the thermostat housing. You have to do a little trimming, on many supplied gaskets.
I used a combination of Eagles methode and another that was mentioned in a thread awhile back.
I removed the temp. sensor from the rear of the block and filled (slowly) until coolant came out (motor off), replaced the sensor. Then used Eagles methode to top it off (had to add very little coolant). Also squeezed the top radiator hoses a few times with the motor at operating temp. Been going a week now and haven´t had to add any coolant. Seems most all of the air is out.
Check close for leaks, a small leak, will loose a little coolant (hardly noticeable), but will also suck a little air, when the motor is off. The air builds up and causes problems.
Many replacement thermostats, not OEM are a little to tall to fit properly in the XJ housing, if installed in the wrong position, they will crush a little and cause problems.
I just opened a junk, 87 OEM radiator (curious) and found an amazing amount of calsification in the bottom. Doubt any amount of flushing would have removed it.
I used a combination of Eagles methode and another that was mentioned in a thread awhile back.
I removed the temp. sensor from the rear of the block and filled (slowly) until coolant came out (motor off), replaced the sensor. Then used Eagles methode to top it off (had to add very little coolant). Also squeezed the top radiator hoses a few times with the motor at operating temp. Been going a week now and haven´t had to add any coolant. Seems most all of the air is out.
Check close for leaks, a small leak, will loose a little coolant (hardly noticeable), but will also suck a little air, when the motor is off. The air builds up and causes problems.
Many replacement thermostats, not OEM are a little to tall to fit properly in the XJ housing, if installed in the wrong position, they will crush a little and cause problems.
I just opened a junk, 87 OEM radiator (curious) and found an amazing amount of calsification in the bottom. Doubt any amount of flushing would have removed it.