Coolant loss 2001 Pathfinder XE

[Modifyit]

Noticed coolant loss and high temp but can locate no external leaks. No vapor or steam from exhaust to indicate internal leak and no coolant in engine or transmission oil. Have topped off the radiator several times and perhaps now have all air out to the system. After last long test drive with A/C on, coolant level in the radiator is full after complete cool down.

I am wondering if I have the correct radiator cap. When I purchased the cap approximately 6 months ago, I asked for a cap for the correct year and model etc. I did notice a number stamped into the cap which is 6.0. No indication of what the number refers to and I doubt this Pathfinder would use less than a 13 to 15 PSI cap. If this number (6.0) refers to PSI, then I believe it is rated too low. Maybe that would account for a slow coolant loss.

Any ideas on this loss of coolant?

[smj999smj]

There's a saying, "If you're not leaking it, you must be burning it!" I would get a "no spill" funnel on the radiator and top it off so that the coolant fills the bottom of the funnel. Turn the heater on to maximum temperature, which will allow coolant to flow through the heater core and purge out any air. Jack the front end up, which allows any air to purge out more easily. Run the vehicle at a steady 2500-3000 RPM and keep an eye on the coolant in the funnel; this is basically a good way to purge air out of the system, as you can see the air bubbles as the come up through the top of the radiator, into the funnel. Eventually, the bubbles should stop. If you notice the bubbles never stop, this could be a sign that combustion gases are entering the coolant jacket through a failed head gasket. Causes for high coolant temps at highway speeds (and when the coolant level is not low) can include a faulty thermostat, restricted or clogged radiator or air blockage through the A/C condenser and radiator cores. Overheating at low speeds and idle but not at highway speeds would indicate a probable faulty fan clutch. As far as the radiator cap, I prefer to stick with genuine Nissan parts when it comes to this part, as well as thermostats. I doubt that it's a 6 psi cap, as there aren't too many systems that are running below 12 psi on modern cars. As to what the "6" refers to, it could be anything! Only way to be sure is to use a pressure checker on the cap or replace it.

http://shop.advanceautoparts.com/p/lisl ... 22970131-P

[Modifyit]

Thanks for the reply and good advise. I was not aware of the Lisle funnel though have seen similar home made rigs in the past. It will be a helpful tool to diagnose coolant loss problems. One more thing I'll have to buy.

I suspect there could be a combustion chamber leak and this method will allow much better monitoring than looking for air bubbles in the radiator fill spout.