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The mysterious overheating Honda

Honda Blackbird sounds good. You do the most obvious, cheapest and easiest solutions first. What he suggests is cheap, easy and obvious, at least according to him. So, I would try what he says first.

In the old days, you can see if the water pump is working all right by opening the radiator cap and run the engine to see if the coolant in the radiator drops when you rev up the engine. If it drops quite a bit, the water pump is O.K., but if it’s bad, it’s not working. Also, if you have cooling problem at low vehicle speed but not at high speed, it’s likely to be a fan problem. This is because at low speed, the cooling system relies on the fan to draw heat away from the radiator, but at high speed, the wind coming through the grill would be enough to cool the radiator. To see if the fan (or components related to it), let the engine run until the temperature rises above normal and see if the fan kicks in. If it doesn’t kick in, it’s the fan.

UPDATE: so I went back to mechanics who diagnosed my car the first time for a bad thermo and fan relay switch. They spent the whole day with it and then I get the call first thing he says “I can’t figure out what’s wrong with this car I’ve spent the whole day with it” he spends the whole day with it and that’s what I hear. So he says everything else has been ruled out and he says it must be a pinhole leak in the head-gasket and this is why their is no milky dipstick or white pummels of smoke. His suggestion to me is to get a head-gasket sealant, I asked if they could do this but they said they don’t like using it. I am skeptical about doing this sort of job myself because I am not mechanically inclined with vehicles. Also I’ve read where people ended up ruining their engines and making the problem a million times worse. What do you all think I should do at this point?

@JimFrost‌

I don’t particularly like the sound of this mechanic, at least not his idea of a fix

If he’s confident the headgasket is faulty, he should recommend replacing it

Stopleak is not a professional repair, in my opinion

that is a DIY product for somebody who is a cheapskate, or wants to mask a problem long enough to sell the car to the next unsuspecting sucker

You need to replace your mechanic. This one is as defective as your car. I cannot begin to list the problems I have with your mechanic’s comments.

There are no “undiagnosable” problems, only people who don’t know how to diagnose them. Like TSM says, you need a new mechanic.

I’m not a believer in head gasket sealer products. To me anyway, it’s mostly snake oil although it’s possible that some coolant leaks not breached into a combustion chamber can be slowed or stopped by some products. The fact that a head gasket may have a non-combustion chamber related coolant leak does not mean for one second the engine will overheat because of it.

I’m still curious about the fan operation and whether or not the problem exists only with the A/C on, off, or both.

The point being that you state it only overheats at idle or low RPMs. At highway speeds A/C head pressure heat will be removed by airflow through the condenser.
At idle and low RPMs unless the fans are operative the heat from the A/C head pressure can cause overheating due to lack of airflow.

Yeah that mechanic can suck a fat one kind of a condescending jerk as well, use a lot of technical terms I wouldn’t know to try and confuse me, when he could just say he doesn’t know. I am just so sick of throwing money at this car. I’ve read pretty good things about blue devil I have a buddy of mine who fixed his head-gasket with the stuff and has his honda at 300k now. I might go with that. The mechanic has checked the A/C everything in the cooling system has checked out the only place left is the head-gasket, and considering these cars are notoriously known for them I would say more likely than not it’s the problem.

Like Sherlock Holmes said, When you have eliminated every other possibility, what remains, however improbable, must be the answer.

And on an old Honda, a bad head gasket is not improbable, it’s quite likely.

@jesmed1‌ that’s what I think is the case. Have any of you had bad experiences with head-gasket sealant? I am ready to try this stuff out, but at the same time am skeptical and worried that I could do more harm than good.