I apologise if this has been discussed in earlier threads, but im having trouble navigating the search function.

I have an Australian RHD 2007 grand voyager 3.3, 125,000 kms bought 1 week ago. since buying it I have put about 240 kilometers on it. Yesterday on the way to work, the heater was blowing cold air, wouldnt warm up. When I got to work, I investigated there was no coolant in the top up bottle.

I put about 3 litres of tap water in there to get up to the max line, and ran the car intermittently through the day, watching for leaks. there are various drips of water underneath the front passenger seat. but I cant be sure that isnt left over spills from when I topped it up. Today it has remained steady but I dont do much mileage.

I immediately suspected cylinder head stuff (being a pessimist) but the oil looks / feels fine, oild filler cap isnt creamy, its oily and black. Car is otherwise running smooth as silk. Exhaust is clear.

Ive bought sufficient coolant to flush and refill the system, (since I put so much normal tap water in), but only going to top up until i think its fixed.

Any ideas on weak points to have a look at. If I cant find a leak, im going to take it for a pressure test.

 

Yes, a pressure test is good on the cooling system. Mysterious coolant loss with no leaks anywhere is usually cyl. head gasket trouble. If this proves to be the case, you need to ensure the heads are dead flat, and the block tops are/is perfectly clean before you install new gaskets. I've seen Chrysler advice NOT to use scrapers on the block tops for some reason, but solvents only to clean them. Whenever I've changed a cyl. head gasket, I've put Blue Hylomar on both sides of the gasket, and retorqued the head in correst order after 500mile.
Nonetheless.... I'd still look very carefully for leaks, esp. tiny pinholes in rubber hoses that only wake up when there is full pressure in the system.

Leedsman.

 

The biggest by far failure after a head job is failure to re-torque after 100 hours of service, some heads can lose 50-60% of their torque in that 100 hours, hence lose their flatness. MLS head gaskets must be flat to no more than .004 inch of distortion on our 2.8 4 pots. A pain in the bum re-torque will take care of most of the issues - as Leedsman says don't scratch the head or change its near mirror [flatness] finish.

[I think Mopar do a .020 performance quality gasket for Jeep high compression ratio's - same as our engine]

 

If you have an Auxiliary heater fitted below the passenger seat (in Australia did he say, sun, sun and sun) check there's no coolant coming out of heaters exhaust exit.