My wife's '88 Nissan pickup (4 cyl Z24i engine, 5 speed, 2wd, 182,500 miles) is almost overheating when the AC is on, even at interstate speeds. I say "almost" overheating, because with the AC on, the needle is just over 3/4's on the temp gauge (just shy of the "hot" line). It used to only go to the exact center of the gauge. With the AC off, it still only goes to the middle regardless of interstate or city driving. All basic maintenance is up to date, including plugs, wires, cap, rotor, one ignition coil, all filters, fresh oil, coolant flushed (twice), thermostat, radiator cap, and new water pump with integral fan & clutch. The water pump was actually replaced twice, because the original one started weeping, and the second one had a "weak" fan clutch according to a local shop. It's currently on a rinse phase of AutoRx with GTX 10w40, but the problem existed before the AutoRx.
Today, I had her run the AC on her way home so I could check the actual temp of her coolant. After only a 5 mile drive, and with the temp gauge showing 3/4's up, the coolant temp was 217*F according to my multimeter. This was after several minutes of her parking it, and venting the pressure to avoid burning myself. Her thermostat is rated at 180*F, and I could tell when it opened while flushing the cooling system the other day. So I think it is good. The coolant is Prestone All Makes, mixed 50/50 with water.
Only things I can think of would be her radiator is partially clogged, or her timing is slightly off. But I'm not sure which one to pursue first, if it's either. With the radiator, I already ran a bottle of the Super Flush through for the several hundred miles per the instructions, then flushed using a Prestone flush kit (the type with the "T" installed in the heater hose). There is an orangish "coating" inside the radiator, but not anything I would consider excessive. Her timing is on according to my timing light, but her idle speed had been messed with, and I only have the idle set by ear. I don't have a tach handy to get the idle speed dead on, and Nissan didn't see fit to install one in the truck even though it is a 5 speed. So the timing could be (and probably is) slightly off. I doubt by much because the truck drives decently, although fuel mileage could be better. I don't have hard data on what the mileage used to be, but now it averages 22 mpg with all city driving. I seem to remember it used to be around 25.
Has anybody experienced this type of problem before? I'm open to all suggestions. If it is the radiator partially clogged, would running another chemical flush do any good, or any harm? And if it is the timing, which way would cause it to overheat (advanced or retarded)? I'm trying to find an inductive pickup tach locally so I can get the idle and timing set perfect, but haven't had any luck. So I may end up having to order one, which would take several days to arrive. And ordering one would also depend on cost, too.
TIA.
Dave
Today, I had her run the AC on her way home so I could check the actual temp of her coolant. After only a 5 mile drive, and with the temp gauge showing 3/4's up, the coolant temp was 217*F according to my multimeter. This was after several minutes of her parking it, and venting the pressure to avoid burning myself. Her thermostat is rated at 180*F, and I could tell when it opened while flushing the cooling system the other day. So I think it is good. The coolant is Prestone All Makes, mixed 50/50 with water.
Only things I can think of would be her radiator is partially clogged, or her timing is slightly off. But I'm not sure which one to pursue first, if it's either. With the radiator, I already ran a bottle of the Super Flush through for the several hundred miles per the instructions, then flushed using a Prestone flush kit (the type with the "T" installed in the heater hose). There is an orangish "coating" inside the radiator, but not anything I would consider excessive. Her timing is on according to my timing light, but her idle speed had been messed with, and I only have the idle set by ear. I don't have a tach handy to get the idle speed dead on, and Nissan didn't see fit to install one in the truck even though it is a 5 speed. So the timing could be (and probably is) slightly off. I doubt by much because the truck drives decently, although fuel mileage could be better. I don't have hard data on what the mileage used to be, but now it averages 22 mpg with all city driving. I seem to remember it used to be around 25.
Has anybody experienced this type of problem before? I'm open to all suggestions. If it is the radiator partially clogged, would running another chemical flush do any good, or any harm? And if it is the timing, which way would cause it to overheat (advanced or retarded)? I'm trying to find an inductive pickup tach locally so I can get the idle and timing set perfect, but haven't had any luck. So I may end up having to order one, which would take several days to arrive. And ordering one would also depend on cost, too.
TIA.
Dave
