I have a 98 Accord EX with 182,xxx miles, replaced the motor last year with one that supposedly had 85,xxx miles on it. I also replaced the upper/lower hoses, thermostat, water pump, timing belt, plugs and wires at the same time. I haven't driven the car all that much, and have only put about 5,000 mi on it since the engine swap, but I seem to be having coolant issues. It appears that I'm losing coolant (level has gone down from near the top of the reservoir to the min line after approximately a couple thousand miles), however I never see a puddle, and haven't noticed coolant on any components inside the engine compartment, or inside the car at all. It doesn't seem to be blowing white smoke from the exhaust, and the oil isn't milky. I have smelled coolant a couple times at idle. Also, the temperature gauge will sometimes fluctuate. It never overheats but the gauge will go up near the top and then come back down to normal, mainly on long trips. Should I start by replacing the thermostat again (possible it is defective?)? Would a bad thermostat cause coolant loss? I also replaced the radiator cap, thinking that might have caused the fluctuation, but didn't seem to help. I have burped the radiator too. Not sure if this is related either, but my oil level seems to fluctuate, from down around the bottom hash mark on the dipstick to 1/2, 3/4 of the way between the top and bottom marks. Is this more likely due to parking on differently sloped surfaces? I always park on the street, and always check the oil when the engine is cold. Sorry for the long-winded post, wanted to be as descriptive as possible. Thanks!!

 

Suggest having a cooling system leak test performed to locate any external leaks. Small leaks due to failing hoses can be difficult to locate.

Low coolant level will cause erratic coolant temp and overheating indications.

For possible HG leak, there is a chemical test that will detect combustion gases in the cooling system.

good luck

 

Unrelated. Check the oil when the car is warm but after it's turned off for more than five minutes, like after filling up with gas. I've noticed that the slightest slope will effect the dipstick reading, probably because the dipstick tube is way off to one side of the engine.