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I'm replacing both the IAC and the IAC to throttle body gasket on one of my cars, but until they arrive in the mail I'd like to put on the old ones and drive the car around.

There is a small chance that this might result in a small coolant leak from the IAC into the throttle body. Would a small amount of coolant getting into the intake for say two weeks / a few hundred kilometers of driving cause any damage?

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Let's assume you have a 2 litre 4-cylinder engine. One cylinder is 0.5 litres, and at 1:10 compression ratio, 0.05 litres when the piston is at top dead center. At 1000 RPM, or 16.67 revolutions per second, or 8.33 intake strokes per second, you have 8.33 * 0.05 litres per second = 0.41667 litres per second of free space above the top of the pistons. Unless your leak is a significant fraction of this, you won't experience any problems when driving. A leak of this proportions would drain the coolant system empty in less than a minute!

However, when parking, and starting to drive after that, the situation might be different. If one cylinder that has only 0.05 litres of free space above the piston gets this amount of coolant, you have a problem, coolant being incompressible. So, do you expect the system to leak about 0.05 litres when parking? If so, I wouldn't even try to start the car, there being a great danger of engine damage. The danger is greater the longer the parking duration is. You could of course check the amount of coolant leaked to the throttle body before even attempting to start the engine.

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  • My expectation is that in the case of a leak it would be fairly minuscule, and would only likely leak if the cooling system is under significant pressure, which is unlikely as it's summer and I would be driving with the AC on, which prevents the coolant from getting above 94*C. If I understand you correctly, my only real concern is the possibility of hydrolock? Sep 12, 2017 at 16:21
  • Yes, that is my understanding, apart of perhaps a little coolant in oil from blowby gases. There is nothing in coolant that would dissolve the aluminum in your pistons, considering that coolant is compatible with aluminum in engine block and cylinder head.
    – juhist
    Sep 12, 2017 at 16:33
  • I was more worried that it might somehow wash the oil off the insides of the cylinders and lead to excess wear, but I guess it would have to be a pretty significant amount for that to happen? Sep 13, 2017 at 6:46
  • If you park the car for a long amount of time, there is probably no oil in the insides of the cylinders as it drains to the bottom. Yet the engine still starts anyway. Yes, there could be some excess wear, but probably not too much.
    – juhist
    Sep 13, 2017 at 11:28

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