Cooling system Problem

[Christopher]

(2003 Honda Civic sedan 1.7L I4)
So my friend called me the other day saying she had a problem with her car. She was driving home from work on the highway at a constant speed. She noticed that the engine temp shot up to about 3/4. She was in a construction zone and couldn’t pull over so she started to blast the heat. She noticed that the heat wasn’t initially hot. Before she left the construction zone the engine temp had come down, and the heat started to blow hot. According to what she’s telling me the engine temp will fluctuate, not super iratically but gradually, and the heat will also fluctuate. Her old mechanic just went out of business and she has to take a trip on Saturday and asked if I could look at it before she goes to see if she’s okay to drive or not. My initial thought was air in the cooling system so when she brings it over today I’m going to bleed the system. While I do that I’m going to make sure that the thermostat isn’t stuck open(by making sure that coolant only starts to circulate when the fan comes on).

I don’t *think* it would be a coolant temp sensor because that wouldn’t fluctuate, correct? It would just be wrong?

This doesn’t sound like it could be a head gasket or water pump issue to me, but I really just wanted to see if with those conditions I’m not over looking anything. I say I don’t think it is head gasket or water pump because of the heat component.

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[Richard Kirshy]

Typical signs of air entrapment.
Do a proper bleeding, use a spill free funnel.

[Christopher]

Update: I bled the cooling system, spill free funnel, and did it until the fan came on twice. Didn’t replicate the complaint after the work. But I did notice white smoke coming from radiator while bleeding it. Is this normal or exhaust gasses leaking into the cooling system?

[Richard Kirshy]

Could simply be steam, but a combustion gas test will answer that question.

[Author]

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