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2000 Honda decreasing MPG and heating issues

Hey Guys, I have had some issues with my 2000 Honda civic. I have had consistent issues with my car getting hot. I have changed the thermostat, temp sender, O2 sensor, spark plugs and wires, fan relay, Air filter, Oil filter and fuel filter. I have also installed a toggle switch all within the last 9-12 months. My heating issues seem to be very random, when I changed some parts out it seems to do good for a bit but then randomly heats up and fast usually when I am idling. I have had 3 mechanics look at my car and help me with the replacement of parts yet even they are puzzled with the issue as the car has been very well taken car of for it’s age but had so many new parts installed in such a short time. On top of that I have noticed my gas mileage drop again, I noticed this before I had changed the temp sender but it went away for some time. The MPG has had a significant drop the past while and as you can imagine does not help the pocket book when you are consistently filling the tank and replacing parts. I am hoping that one of you may have a different thought as to what may be causing me this issue. Please Help!

Honda Civics almost always need a head gasket replaced. I had that done on my '03 Civic 2 years ago at about 150K miles which is pretty typical. If you don’t know if your civic has ever had a new head gasket, that very well could be the culprit.

The breaches are very small and sometimes throw confusing symptoms.

Does the fan com on when it’s warm? Are you losing fluid?

The head gasket is a very possible issue I was just hoping that wasn’t my issue as I have been informed at that point I am better off to do a motor swap.

Yes the fan comes on, it wasn’t for a while but I now have a toggle switch to manually turn it on however with the recent problems it doesn’t seem to be enough sometimes. what is even more weird is after all the work the problem subsided for a cpl months but then started again in a odd way, the first 2 times it happened after all the work was just after I filled the tank. Not losing fluid at least not to my knowledge.

A head gasket job is about $1,100 done properly and might include the timing belt and water pump at the same time. If the motor isn’t burning oil this work could be worth the money. I’d only do an engine swap if the current motor has other significant issues.

Watching the expansion tank can fool you. The fluid isn’t being drawn back into the tank when the motor cools. So, the level stays the same, but if you pop the radiator cap (when the motor is cool) and you find you need to add some fluid to fill the radiator that pretty much seals the deal for me that you have a breached head gasket.

Also filling up the radiator will “cure” your issues for a couple of weeks (even months if you don’t drive much) until the coolant is displaced and you get enough “air” in the cooling system and then your symptoms will return.

On Honda’s a lot of people spend money on new radiators, new thermostats, new radiator caps, but in the end that money would have been better spent on the real problem; replacing the head gasket.

Low mpg is often caused by the coolant being too cold. Is it possible your measurement of the engine temperature is inaccurate, and by turning on the fan with a switch it doesn’t allow the engine to reach normal operating temperature? Have you tried securing an independent measurement of the engine temperature?

No that wouldn’t be the case for me. the gauge is very accurate. At this point I am pretty sure that it is my head gasket and one of my thermostats has now gone faulty as the car has gotten hot enough to fry it I suppose. the fan doesn’t even work anymore when it comes to cooling the engine.I could have the car sit for 9-10 hours and the engine be hot 2 blocks away if I can’t get heat to blow through the vents. The reason I know the temp gauge is accurate is I can literally watch it go up when the heat doesn’t blow through the vent and then go back down when it kicks back in

When the engine is cold, remove the radiator cap.

Start the engine, and as the engine idles watch the coolant in the radiator.

If bubbles start to appear in the coolant, that’s an indication of a beached head gasket.