QuestionHi I have a 87 Jaguar Xj6 and everything water related has been changed (new hoses, thermostat, water pump, fan clutch, therm o switch and the sensor that controls the gauge in the dash) my 4.2 is new as well and I use 50/50 antifreeze. The problem I'm having is the temp gauge, I can drive it and it stays around 90-100c. My gauge start acting erratic after I changed the o2 sensor (don't see the connection). I read your answer to another persons question, your answer:
"Answer Hi Frank,
Sorry about that, I have brain fade at times and I have no idea what I told the other guy. You are right about the temp. The ser III Xj-6 should show about 90 C. all the time. If all of the other gauges are readng correctly then the power to the gauge is probably ok. Jaguar does not use a voltage stableizer like other British cars. The temp sender unit is in the rail on top of the intake manifold. You do need to confirm that there is a ground strap from that rail to the engine at the rear of the manifold. Put your volt meter on a low volt scale and check to see if there is any voltage between the engine and the negative post of the battery. I found this to be a problem on several ser. III Jags. If you find voltage there correct the ground of engine to frame. If you find this you must right away get some anti electrolisis coolant additive for the cooling system. Available at truck supply stores. You would not believe what damage this can do. Then you need to check the temp of the top of the radiator. Then check the temp of the coolant rail with all of the sensors in it. They should match and be in the 90 deg C. area. I don't have specs on the ohms of the sending unit but I have two ser. III Jags and they both read correctly so I will ohm them and get the readings to you today or tomorrow."
You stated "confirm that there is a ground strap from that rail to the engine at the rear of the manifold. Put your volt meter on a low volt scale and check to see if there is any voltage between the engine and the negative post of the battery. I found this to be a problem on several ser. III Jags. If you find voltage there correct the ground of engine to frame. If you find this you must right away get some anti electrolisis coolant additive for the cooling system. Available at truck supply stores. You would not believe what damage this can do"
I check my rail and I didn't see a ground from the engine to the rear of the water rail. By not having the ground could that be the reason my gauge goes past 100c. Now I don't hear no bubbling, I have no leaks and I don't smell anything.
AnswerHi Robert,
Smelling or listening are of no use, so you need to run the tests I outlined.
You need to start form scratch and assume nothing. A new engine does NOT rule out problems in the engine and not hearing bubbles does not rule out anything, and not smelling antifreeze does not rule out a leak in coolant.
You must use a systematic testing procedure to find a problem (if you have one)
If you don't have the tools, you need to get them. I have been working on Jaguars since 1960 and I can't fix any kind of car without tools.
You need a volt/ohm meter, A thermal gun, Dye for the coolant test of CO/HC and a timing light.
1. Put the dye in the coolant and follow the directions on the container. This is a test for a leak of combustion into a coolant jacket.
2. Set the ignition timing to specs.
3. Put you volt meter on Low DC voltage and test the O2 sensor out put voltage when at idle. (.5v is normal, below is lean, above it rich mixture)
4. check for Low DC voltage between the coolant rail and the engine and (-) battery post, while idling and at cruise RPM.
5. Check temp of coolant rail and top hose connection on the radiator with the temp gun (a meat thermometer will work)
6. Check the radiator fan clutch.
7. Note if the overheating is only on the highway and will the temp come down while idling.
8. Have someone rev the engine a few times and be looking carefully at the lower hose to see if you see any signs at all of the hose retracting.
9. Test for Low DC voltage from the temp gauge case to the (-) post of the battery
10. Test voltage at the green wire on the gauge while in operation.
I have not found a good test for a partial stopped up radiator but it usually showed up as a overheating at speed but not idling. A radiator shop can run that test. Don't forget to test the thermostat as I have at times found bad new thermostats. Don't run without a thermostat!!!
Let me know,
Howard
Somewhere in the above tests you should find the problem.
