Hi everyone. Thanks in advance for taking a look at the problems I have been having. I have a 99 Honda Civic Si with about 147,000 miles on it. Car problem history: had a valve leak in the engine about 2 years ago and had it semi-rebuilt at that time from a very reputable shop. Current problem: About 2 weeks ago we had a real hot spell in Seattle. As I was driving the vehicle on one particularly warm day, I noticed that my temperature gauge was increasing to dangerous levels so I slowed down, pulled over and let the engine cool down. I was able to get the car home where I then proceeded to check coolant level (which was fine) and found that the reserve tank was completely full. Baffled, I took my car to the shop where they suspected a bad thermostat, which they replaced, and also checked and re-grounded my fan and auxiliary fan. Having thought the problem solved, I drove the car on a small trek down the highway (about 20 to 30 miles) and once I exited, found that my car was over heating again—not on the highway, but when I came to a stoplight at the exit ramp. Baffled and pissed I took my car back to the shop where they mulled over the problem…part of the problem being that they could not get the car to overheat themselves while idling it and running it at the shop. Long story short, they could find no reason as to why the car was overheating occasionally (radiator looked good, fans good, yada yada). An important point to note, is that when the car does overheat, it seems to “correct” itself, and after a few moments (usually when I give it some gas, or start moving again after a stoplight) the temperature gauge will go back to normal. Vaporized coolant bubbles in the tubes? The shop being as baffled as I was, I took the car for a short drive to try and get it to overheat so they could better diagnose the problem. I drove it around the block a few times and then, after no results, let it sit and idle on a side road. This is when it began to overheat again, so I took it back to the shop where they hastily ran tests while it was symptomatic to try and diagnose. Several hours later, they called me to tell me they suspected a blown head gasket because of hydrocarbon emissions in the coolant. They placed a large funnel over the radiator cap area and revved the engine to show me the geyser-like eruptions of coolant. I was somewhat convinced, however, several questions seem unanswered in the diagnoses—not only that, but they had to idle the car for 5 hours in order to get the geyser-like eruptions. Why was my car correcting itself? Why was there a normal level of coolant if my engine is essentially burning it? They DID say that my coolant was low the second time I brought the car in, so I suspect the faulty thermostat caused the blown gasket—either that or the radiator is bad. I can’t quite figure this one out and I could really use some advice/expertise from some of the car folk out there. I spoke with a garage in Minnesota that I find quite reputable and explained the situation—after telling them that a pressure test on the engine yielded no coolant leak through the plugs, they were more suspecting of a restricted radiator or something more to do with that, than the engine. I should also note that the oil is clear, no milk shake, and that the car seems to be running fine besides the creeping gauge. I’d really like to hear that in fact this is not a blown head gasket—the pressure test on the engine makes me skeptical, as well as some of the self-correcting behavior, and the fact that the car doesn’t want to overheat when actually driving it…more of an idle thing. Any thoughts on this will be greatly appreciated and I thank you in advance for your opinion. Take care, Joe.

 

Welcome to the forums... i have a 1991 honda civic that is doing the same thing.. brand new radiator hoses thermostat and coolant.. i know it isnt the head gasket.. about 3 hours ago i went out there and replaced the temp switch in the block and it doing fine now... try changing that little switch.. its located in the block right below the distributor and it should be a 1 prong adapter they occasionally go bad or come from the manufacturer faulty.. and autozone, advance autoparts, o'rileys or any auto parts store should have them for no more than 20 buck and all you need to do is remove the distrbutor get a deep well 13mm socket and swap them out...

 

one other thing to think on, if the rad fluid has not been changed once a year, or flushed for a long time, the top of the rad can get clogged by poor anti freeze and time. take the rad out and back flush it, or have it cleaned out by a shop. This will take the rad out of a hot condition. When you changed the timing belt, did you also replace the water pump?