I can't speak for the Miata, but I can vouch that a head gasket failure=20 can cause overheating without enough symptoms to be recognizeable. I=20 had a pontiac with the L4 engine which is notorious for head gasket=20 issues - and after months of trying to hunt down an overheat issue, one=20 morning it finally did provide enough leakage into the exhaust that the=20 very first turn over of the engine produced a nice cloud of white smoke... Even then, it took the shop a bit to figure out that it was a leak - I=20 think the problem was more that the exhaust gases were getting into the=20 cooling system than the other way around. It wasn't until they=20 pressurized the coolant system, let it set for a while and then re-crank=20 the engine and see the resulting cloud that they believed me and=20 replaced the head gasket and make the cooling issues go away. -forrest On 6/16/2011 11:32 PM, PICdude wrote: > Quoting John Gardner: > >> One more time - Leaking head gaskets should be ruled out by someone >> who knows how to find them. Eyeballing the coolant reservoir is not good >> enough. It's a common failure in elderly engines,& the initial symptoms >> are exactly what you describe. > If there is a head-gasket leak, where is the fluid going? If into the > cylinders, there should be whitish smoke, if into the oil, the oil > will be murky/milky brown, and if outside the block, it should be a > visible somewhere. If the fluid level is dropping at such a low rate > that it's not even noticeable over some days, then something else is > causing the overheating. > > Cheers, > -Neil. > > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .