Nissan Repair: QX4 Losing Coolant, losing coolant, coolant system

Question
QUESTION: I have a 1999 Infiniti QX4 (V6). It started leaking coolant (noticed when it overheated two years ago) and now uses about one gallon of coolant/year. I keep the overflow filled to the MAX line and it runs fine as long as I do.

I noticed it occasionally drips coolant on my driveway - under the front differential, so toward the rear of the engine compartment.

What is the most common problem in this situation? What is the most economical fix?

FYI. The engine runs fine as long as the coolant is kept full. It just passed a smog test. There is no smoke coming from the exhaust. The oil and oil cap is clean.

A mechanic looked at it and thinks the coolant may be leaking from the head and dripping down there, but he is not yet sure. I want to get an expert opinion.

ANSWER: Hi Ron -

Your mechanic could be right, although there are many ways coolant can leak out of the engine. Most common is the water pump, heater or radiator hose, or even an expansion plug.

My suggestion would be to have the cooling system pressure checked. Hopefully the leak will show up and you can repair it.

Hope this helps -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: Aloha Calvin,
Thanks. As I said I am losing about one gallon of coolant per year and have no other signs of more extensive damage. I can keep the vehicle at correct running temperature just by making sure coolant reservoir is maintained at MAX (requires I had a small amount every 2 months or so).

I would like to avoid costly repairs and wondering if using a sealant or antifreeze with sealant in it could seal this what must be a very small leak on the outside of the head gasket.

The oil and oil cap have no sign of water/antifreeze leaking into it, the coolant has no sign of oil leaking into it, and the vehicle just passed SMOG, and there is no visible smoke or water coming from the exhaust.

Do you like any of the head gasket/coolant system sealants on the market?

I understand the key to using them is to bypass the heater core when installing.

I have heard that Chrysler used to make an anitfreeze with a small amount of sealant in it just to keep small leaks from forming.

Answer
Hi Ron -

I usually do not recommend sealants for the cooling system, as they can clog it up, causing more harm than repair in the long run.

As mentioned, I would pressure test the system. First, inspect the engine for any wet areas. Dry it off, and then proceed to pressure test the system. Look for the leak. Who knows, it just might be something simple, like tightening of a hose clamp or something like that.

Hope this helps -
aloha
calvin