temperature fluctuation 95 ZJ 4.0L
 

I have a 95 Jeep Grand Cherokee 4.0L whose temperature gauge started all of sudden to slowly fluctuate between 200 and 220 deg. F.

I'm thinking there's a problem with the thermostat, CTS, temperature gauge or possibly the water pump.

The 95 ZJ 4.0L runs great with no coolant leaks. Has a newer OEM Mopar two row alum. core radiator. NMCP Heavy Duty Engine Cooling with an OEM transmission cooler.

Looking at thermostats on RockAuto, there's listed several types and brands.

STANT 30109 Premium 195F
STANT 45359 Superstat 195 Degrees (2-1/8" x 29/32" x 29/32)

MOTORAD 2000195 {#19114386, 65009} High Flow 195F
MOTORAD 7200195 {#70095} Fail-Safe 195F
MOTORAD 200195 {#19114427, 20095} OE Standard; 195F
MOTORAD 200195JV {#20096} OE Standard; 195F
MOTORAD 5180KT OE Standard; Kit 195F; Includes housing, thermostat and gasket

GATES 33009S {Click Info Button for Alternate/OEM Part Numbers} Premium; 195º Superstat (2-1/8" x 29/32" x 29/32")

I'm thinking if the CTS and guage are working properly the problem is likely the thermostat? The water pump not leaking or making any noise.

I think the problem is a leak as today I needed to add 3/4 - 1 gallon of dist. water to the radiator as well as fill up the recovery tank.

I found some green coolant on whatever is just underneath the radiator.

If not the radiator cap I'll need to inspect closer for the source of the leak, which would more likely be a radiator hose as the oem Mopar radiator appears in good shape. A newer OEM with a two row alum core and plastic tanks. I guess it's possible as I think plastic rads have been around since the 1980s? I don't remember seeing any Mopar plastic radiators from the 1990s?

The one I have appears to be fairly new, however plastic rads don't rust and age as do the metal ones.

Hmmm..Because of the temperature fluctuation I don't think it would hurt to change out the thermostat even if you found a leak. Sounds like it could be sticking. Fail safe one are the best because they stick open when they go bad. I toasted a head gasket once from an overheating XJ... Pay it safe man!

I try to keep safe.

I'll probably order from RockAuto another radiator cap or two and a thermostat, either fail safe and/or high flow. If I don't have a spare, will order a new CTS in case the one in the ZJ goes bad.

Since I got the 95 ZJ a while ago installed a new starter with lifetime warranty as the ZJ all of a sudden would simply not start. Traced the problem to what appeared to be the solenoid but Rock Auto had a good deal on a Remy starter with lifetime warranty. So ordered the entire starter rather than only a solenoid as the problem may have been the both the starter and solenoid.

During the fail to start problem ended up (for the ZJ) with a spare ignition switch and key cylinder lock with key. Ignition switches and key cylinders do fail, recently replaced a friends XJ ignition switch. His XJ would start then shut off, the problem turned out to be a bad ignition switch.

I've order lots of parts for my 98 XJ the past ~12 years so I may have an extra new thermostat stored somewhere as the XJ and ZJ 4.0L use many of the same parts.

I keep spare parts, filters and fluids, which I try to order in bulk. Have extra synthetic oil, found a dozen Mobile one extended oil filters and a dozen Amsoil EA oil filters that fits both 4.0L vehicles. Cost for each filter after shipping $8.00.

Ordered a case of 12 of Zerex GO-5 one gallon full strength anti-freeze which should last a while as antifreeze has no shelf life.

Installed a coolant filter for the XJ and purchased another one to install on the ZJ. Dirt, slime, corrosion, small pieces of metal, etc. gets into the coolant, using a coolant filter there's less worry about changing the coolant.

Installed reusable lube locker gaskets on the ZJ's differentials and a reusable Mopar gasket on the ZJ's 42RE transmission.

I have one of those inline atf filters installed on the XJ which I replaced the ATF with Amsoil and may install an inline filter for the ZJ just to be on the safe side.

Also replaced the ZJ's transmission oil pan with one that has a drain plug.