Exactly a year ago I was losing about 4-5 ounces of coolant every 500 or so miles. No visible leaks detected, took it to the shop, they pressure tested it & a hose underneath the intake went ahead & gave way, solving that mystery, or so I thought. Few monthes later the issue is back. Shop called today & they pressure tested it a couple times & thoroughly inspected the entire cooling system, found nothing ?! So I ask the wise Jag lot here, where is my coolant disappearing to lol !?

 

Check with a CO2 leak detector to eliminate (or confirm) a possibility of a small head gasket leak.

 

Hopefully it's not a head gasket. I had a 280Z a few years back that did that, but the failure was internal and it was leaking into the #6 cylinder. The top of that piston looked brand new as all the buildup was cleaned off. Pull the plugs and shine a light down there; if you have a shiny piston top ...

 

Guess I'll delve deeper, just got it back from the best local vintage import shop, it passed inspection w/ flying colors but what is a classic Jag if without a quirk or two lol ?!

 

Got my "low coolant" warning on cue @ about 550 miles Friday, today I tested & the head gasket is fine. Pulled the plugs & everything looks as it should, I be damned if I know where this coolant's going lol ?!

 

A random thought: maybe the overflow bottle down by the front of the car is slightly leaking and so the excess fluid isn't there to be drawn back into the system as it cools down?

 

KC, take a look at these 2 more closely. If you have a telescopic mirror (mechanics mirror), take the center panel behind the throttle body off before heading out for a long drive. Preferably while the engine is still running, use the mirror and a really bright flashlight, check for any wetness or slow drips. I have also seen expansion tanks with hairline cracks leak on the underside where you don’t normally see them and because the heat accumulates directly under the hood with the engine off, everything cooks. Another area of concern is maybe making sure that the expansion tank cap holds system pressure. That overflow tank behind the fog light has a large opening that easily vents hot coolant to atmosphere.