92 Civic 1.5 bubbles in radiator

I have a 92 Civic 1.5. If I open the hood (bonnet), leave the radiator cap off and run the motor slowly, small bubbles appear in the radiator cap aperture (Not in the expansion bottle). So, thinking this was a
sign of a blown CH gasket (and there was also some pressure buildup in the hoses), I had the head skimmed. At the same time, I had all hoses, radiator, rad cap and thermostat replaced. But after skimming, the bubbles are still there. My mechanic seems to think this means I should now have the engine block skimmed, I think because of the danger of pressure building up in the hoses from said bubbles. But another mechanic I spoke to for a second opinion said all Civics blow bubbles (something to do with being a high-pressure system). Does anybody know if all Civics blow bubbles under normal conditions? There is absolutely no sign of oil in the water, or water in the oil, or white gunge under the radiator cap (noted from another post to this forum). Water usage is very small but I am not sure if it is significant about 1 cm on the expansion (overflow) bottle after a 400 kms hard (fairly high revs) drive. I am not sure how much water such a system should use the overflow bottle was correctly filled to MAX but not beyond in order to leave enough space for expansion, so presumably in theory the cooling system should not use any water at all, as it is not open to the atmosphere, but does practice match the theory? The temp gauge does not budge from normal. Any comments much appreciated.
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Has the thermostat on the dashboard ever gone well beyond its usual position indicating overheating?
Some coolant leakage/evaporation is normal. Figure adding maybe two cups a year.
If the level in the reservoir goes down suddenly, then one should be worried.
You should check the reservoir level right after driving the car for 30 minutes or longer. Top it off to max after this period.
You may just have air in the system. A proper purge is important. Notably, where the instructions for purging say to idle the car until the fan comes on twice, it typically takes over 40 minutes for the engine to get this hot.
Kinda extreme to have the head skimmed. You had a new head gasket put on, too, right? And the car has never overheated?? Just these bubbles were seen?
the radiator cap off and run the motor slowly, small bubbles appear in the radiator cap aperture (Not in the expansion bottle). So, thinking this was a sign of a blown CH gasket (and there was also some pressure buildup in the hoses), I had the head skimmed. At the same time, I had all hoses, radiator, rad cap and thermostat replaced. But after skimming, the bubbles are still there. My mechanic seems to think this means I should now have the engine block skimmed, I think because of the danger of pressure building up in the hoses from said bubbles. But another mechanic I spoke to for a second opinion said all Civics blow bubbles (something to do with being a high-pressure system). Does anybody know if all Civics blow bubbles under normal conditions? There is absolutely no sign of oil in the water, or water in the oil, or white gunge under the radiator cap (noted from another post to this forum). Water usage is very small but I am not sure if it is significant about 1 cm on the expansion (overflow) bottle after a 400 kms hard (fairly high revs) drive. I am not sure how much water such a system should use the overflow bottle was correctly filled to MAX but not beyond in order to leave enough space for expansion, so presumably in theory the cooling system should not use any water at all, as it is not open to the atmosphere, but does practice match the theory? The temp gauge does not budge from normal. Any comments much appreciated.
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Thanks for the reply. Correct, a new head gasket was put on. The thermostat stuck, and the engine did overheat, but never seriously (if that is possible). The temp gauge was at the top of the thermometer symbol when noticed instead of at the bottom of the symbol, i.o.w. the gauge never went to the top of the range (not sure if this is "well beyond" or significant). But after the thermostat stuck, it was replaced but the head was not skimmed, the bubbles were only noticed about 6 months later and the real reason the head was skimmed was because the top of the (good condition) radiator sprang a leak which prompted the mechanic to look for a cause. Mechanic said that the pressure in the main hose was the cause of the leak as pressure was too high and would land up bursting the hose while on the open road one day.
As an aside, how does one predict a thermostat sticking, should one pro-actively just change thermostats like cam timing belts and just change them after X kms regardless of whether they are showing any signs of packing up?
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So from looking at my own 91 Civic's temp gage, I see yours went about 3/4 of the way between "C" and "H." Your Civic definitely overheated. The only thing I can say with confidence is that the chances of a blown headgasket go up with each overheating episode.
My thermostat seemed to be working fine when I pro-actively changed it at 151k miles. First because it's very inexpensive to put in an OEM one. Second because, from general reading, I expect most cars go through at least one thermostat in their lives. Third, from general reading, many folks do pre-emptively change their thermostats.
There are tests one can do on a thermostat but given how cheap it is, I'd just slap a new one in. Always go with an OEM thermostat. The cost difference is small, and one will then have the confidence that they have precisely the correct design temp settings on the thermostat.
Also, FYI, c. early 1990s Hondas are usually on their second radiator by now. So yours could be said to be par for the course. IIRC leaks at the radiator top are a common cause for replacement. Aftermarket radiators are fine.
I suggest you do a proper air purge (if you can handle a 10 mm wrench, you can do this) of the coolant system, monitor the coolant levels, and report back. See autozone.com's free online repair manual (or your owner's manual) for the directions for purging. Have a magazine while you wait the 40 minutes or so for the fan to come on twice. Only use OEM coolant (or maybe orange Havoline). Hopefully your mechanic used OEM coolant.
Thanks for the reply. Correct, a new head gasket was put on. The thermostat stuck, and the engine did overheat, but never seriously (if that is possible). The temp gauge was at the top of the thermometer symbol when noticed instead of at the bottom of the symbol, i.o.w. the gauge never went to the top of the range (not sure if this is "well beyond" or significant). But after the thermostat stuck, it was replaced but the head was not skimmed, the bubbles were only noticed about 6 months later and the real reason the head was skimmed was because the top of the (good condition) radiator sprang a leak which prompted the mechanic to look for a cause. Mechanic said that the pressure in the main hose was the cause of the leak as pressure was too high and would land up bursting the hose while on the open road one day.
As an aside, how does one predict a thermostat sticking, should one pro-actively just change thermostats like cam timing belts and just change them after X kms regardless of whether they are showing any signs of packing up?
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snipped-for-privacy@ru.ac.za wrote:

avoid this person. seriously. hoses bust when they're old, and if they're chemically challenged as can happen with long term gasket leakage, or if the radiator pressure relief system is somehow malfunctioning, but gasket leakage alone cannot burst a hose if these other problems don't exist.

yes. i think it should be a higher priority item than coolant pumps and oil seals that so many shops replace preemptively.
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snipped-for-privacy@ru.ac.za wrote:

forget about the hoses - the radiator cap has a pressure relief valve. avoid any "mechanic" that doesn't know that.

absolute bull!

yes, i know. they absolutely don't.

hardly ever happens with blown civic gaskets - they blow gas direct into the coolant jacket.

sounds like you have a cracked head or block. at this stage, it's time to stop wasting more time and money on this engine and just buy a "new" one. low mileage used jdm engines are shipped all over the world - you're bound to be able to get one for a reasonable price.
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