My daughter called me last night and the overheating light came on while she was on the way home from work yesterday...... I showed up and put 1 1/2 gallons of water in the system..... then I pressurized the system to 15 pounds and it held for 10 minutes and I saw no leaks anywhere..... the vehicle has been run just fine for a day now and the level has not lowed............. testing for a head gasket problem came back negative...and there are no systems of a head gasket problem....... 2 months ago I replaced the intake manifold gasket....... so what else could cause the water/antifreeze to have "lowed"??

Thanks

Is the carpet wet under the dash on either side?

What were the conditions under which it over heated?

No, it is not wet

I don't know what the conditions were, my adult daughter was driving on the highway and she gave me a call that it was overheating......

I wonder about coolant hoses. The big ones - radiator hoses, heater hoses, etc. - that I assume you've checked . . . and the small ones like the little bitty ones going to the throttle body etc.

Held 15 pounds with my pressure tester for 10 minutes....

Pump it up to 20 pounds. Pressurize hot engine and see.

dandyd, it'* possible after doing the intake manifold job you had an air pocket in the cooling system. I know it'* been 2 mos. since doing that project and you would think that the overheating would have manifested itself before this if that was the case, but perhaps the driving conditions were more extreme prior to overheating this time. And if your daughter is anything like mine, the hood rarely comes up and she would not have noticed the low coolant reservoir level as the air pocket eventually purged. Once you're satisfied you have no leaks, don't forget to replace that 1 & 1/2 gallons of water with a 50/50 mix of the proper coolant.

Look at the water pump for signs of seepage (white crusty trail from behind the pulley). Have seen these seep on cool down and not leak while driving or under pressure cold. Won't always have a drip due to evaporation from a hot engine. Just something to look at.