Hello,
I recently replaced the thermostat in my 2010 Honda Civic with the 1.8L. So far, the engine gets up to temp and the heat is nice and hot.
However, I went for a drive this morning and noticed when I turned the heat to about max, the temp gauge went down a few bars (fyi, it was about 40*F). Immediately, I turned the heat off and the car did eventually warm up and maintained its operating temp. At that point, I was able to use max heat without any issues.
Here’s my question — is it normal for the engine temp to go down while the engine is warming up (in cold weather), alongside the heat being used close to max? Like I mentioned, once the temp got up it never fluctuated, even when I put the heat on max. I doubt there’s anything wrong and perhaps it’s me being a little paranoid!
Thanks!
Luke
Sounds extremely likely that you did not follow the proper cooling system air purge procedure. The hardest area to get air out of during the purge procedure is the heater core. The heater core dissipates heat into the cabin of the car and your symptoms would be explained by air in the system. Some systems are really stubborn to get air out of and sometimes it helps if the air is trapped in the heater core if you park on a hill so gravity helps to force the coolant in and the air out.
If you are having a hard time with this I would bring it in. Its not worth damaging the engine over something small and relatively cheap and I have seen cars come in with damaged engine internals just because the cooling system was not properly purged of air after a leak situation.
@inthedetails
Thanks for the reply! I brought the car to my mechanic. Do you think he didn’t bleed the system correctly? And you mentioned parking on a hill. Will that fix my issue?
If you park on a hill AND redo the air purge procedure it will most likely fix the problem. The alternative is that there is a very small leak that has been missed in either the heater core or the radiator that is creating an air pocket. Its also possible (but unlikely) that the head gasket is bad. However, I wouldn't panic. Doing the simple fixed first to narrow it down is the best route to take and there is a very good chance you will resolve the problem by simply purging the air.
It is possible your mechanic thought he/she had already purged all of the air out. Sometimes cooling systems will behave normally during a test drive and start acting up later. This is why very good mechanics take a length road test after the cooling system has been repaired. Like I said before though, some cooling systems can be very stubborn especially if there is a dual zone heating system.
@inthedetails Okay. Thank you for thoroughly explaining everything! Much appreciated. I had to deal with little to no heat and a fluctuating temperature gauge for about a year, so after getting things fixed and still dealing with a similar problem definitely makes me more concerned. I will have to bring my car to the mechanic and see if he can purge the air out. I’ll make sure to update you on that. Again, thanks for all the help!
Anytime! Feel free to post back here once you find a resolution or if you don't I can help walk you through other options.
Greetings,
So I just got off the phone with my mechanic. I explained to him my situation with the fluctuating temperature gauge, making sure to mention a few things you had said (specifically, redoing the air purge procedure).
He seems to think everything is fine, but did tell me a few things:
1) Referred to the air pocket as "steam"..... (same thing?).
2) Told me that if there is air, it would actually cause the engine to overheat.
3) Recommended adding a small bit of coolant into the reservoir.
4) Said that the air pocket will most likely go away by itself.
My mechanic is very reputable and has been in the industry for 30+ years. I doubt he'd give me any bad advice. But I still wonder if this could be an issue. He told me not to worry much about it. Let me know what you think.
Thank You!
@inthedetails
UPDATE
I ended up not doing anything, as I've been busy. However, I've noticed as time goes by, the thermostat has "adjusted" and doesn't seem to go back down anymore. Hoping nothing changes, knock on wood!
If you live somewhere that stays below freezing for weeks at a time then I would recommend wedging a piece of cardboard over the front of the radiator (covering about half of it) to ensure the engine stays at operating temperature. Just make sure when it warms up again to take it out or you may overheat.
