'coolant leak but hoses are fine'...? If it has a leak, where is it coming from?
your possibilities for overheating are varied on a Mark viii, things to check are the coolant fan-does it come on when you let it idle for a long period of time, NO air conditioning on? If not, your VLCM (variable load control module) is bad, it is located next to the suspension compressor, passenger side fender under the intake filter. Check fuses and relays too, you might luck out and find it is just electrical. That fan takes a lot of juice (60 amps!) so make sure your electrical system is in good shape-even the 130 amp alternator you have is barely marginal, I have a 200 amp in mine, it is a good thing. Water pumps on these are easy to replace, one of the easiest I have ever seen, so consider it. Also a Cobra pump is a better alternative to the stock pump.
there may be air in the system, these cars are prone to this and have to be filled properly after servicing the cooling system-the front of the car should be a little higher than the back, and after filling the surge tank, remove the cap to the crossover tube (1/4" drive rachett) and start the car, let it run and fill at the crossover tube until it dribbles out of the top-screw on the cap, drive it, and if necessary, check it after it has fully cooled down to see that it has no air in it. Your surge cap may be defective, and people HAVE installed the thermostat upsidedown, so you may have to double check that. And, id you have a leak, it needs to be fixed-the system should hold pressure when it reaches operating temp, you can check this by squeezing the top radiator hose, it should be impossible to collapse. there's always the possibility of a blown head gasket, but it would run badly, smoke out the exhaust, you'd find oil in the coolant or coolant in the oil-hope that is not the problem, these are a pain to do since it is a DOHC engine.
Purge system and check for leaks at the heater core ,maybe water pump is going out same thing happened to me turns out blades inside waterpump rusted away
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The car sat for 2 years when it overheated the first time it just shut down. The system has pressure cannot collapse the hose, the fan also turns on. Don't see any leaks but had to fill the coolant but not since then.
The cross over tube is that next to the air filter on the passenger side front? Took cap off looks like a tire valve with coolant on top of it. When I shut the car off could hear gurgling from top hose of radiator
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