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Hey everyone I need some help diagnosing whats wrong with my civic. I got a 94 LX and it started overheating the other day. It has a brand new radiator, thermostat, and hoses. The oil isnt mixed with the coolant so Im gonna rule out a head gasket leak. The car runs and it looks normal but quickly overheats. Also when I put it in D or R and hold the break the idle jumps and so does the car. Its as if Im stepping on the gas pedal as im holding the break. Any thoughts?

 
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Civic + overheat = headgasket

https://www.civicforums.com/forums/3...reference.html

^ this is specifically for newer gens but the information is relevant.

Civic's don't 'milkshake' the oil when when the HG goes bad. Pressure bleeds into the coolant generally and eventually overflows the coolant reservoir.

 
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The thing is it overheats as soon as I start it. Ill start it and let it run for a little and if I take it around the block once the temperature will jump. As if there is absolutely no coolant going to the engine. Maybe the thermostat is shot?

 
Rep Power: 518

You need to be checking more than just the gauge on the dash.
It could easily be lying to you.

 
Rep Power: 210

then why not start by check it?

where are the coolant levels in the rad? in the overflow bottle?

see where they are cold, then see where they are hot

 
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i have have dealt with allot of cars lately that have had overheating problems and the most common problem was either leaking or air in the system. the heat jumping like that sounds exactly like their is air in the system that's usually what happens is it gets air going through the engine block then bam you have overheat, although it usually fluctuates up and down very quickly... it could also be that you have a clogged heater core or a very small leak that is letting in air. first i would test your coolant for
compression gasses. next i would rent coolant pressure gauge... you tube how to do these things if you don 't know how it's pretty simple. if you have compression gases... it's a head gasket. if not proceed to test coolant pressure. if you pump up your gauge and it slowly loses pressure then you have a leak somewhere. if you don;t find any thing wrong after this i would suspect a clogged heater core or a closed shut thermostat, since you said the thermostat was recently replaced then it would be a clogged heater core. let me know if you have any questions. do very intense diagnosis, do not just throw parts at it.

 
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I would guess a sticky thermostat, even tho you get one brand new, it might be defective. Check by putting it in almost boiling water se if it opens up