I just had my radiator cleaned, and now the engine is running very cold. The temperature needle is barely moving. Are there any long term reliability problems that I should be worried about? Will running with a colder engine cause any damage?
Yes, running a cold engine will waste gas, cause additional wear to your engine’s insides, and perhaps even other problems to the emissions components by keeping the ECU operating in the loop of bypassing the oxygen sensor thereby allowing it to keep running rich.
First suspect is the thermostat. It’s probably stuck open. It costs less money than lunch for one at a family restaurant and is really easy to change unless it’s in a poorly accessible location (most are not).
Most likely, you just need to have your thermostat replaced, which is a relatively cheap procedure on most cars.
Yes, running with a colder than normal engine can cause damage, as this accelerates engine wear, and it drastically decreases your gas mileage. Your oil will need to be changed more often, and the unburned gasoline going into your catalytic converter will lead to an early demise for that very expensive part.
Thermostat replacement is cheap enough that you should not think twice about whether to do it or not. By having it replaced, you will most likely save enough money on gas in one month to pay for the replacement.
As mountainbike & VDC have noted this is probably a simple and cheap thermostat problem. So simple that it is probably not worth asking your shop about - but if you mean that they just flushed the cooling system, sometimes the thermostat is removed for this procedure. Maybe this shop does this and someone just forgot to put it back in. Check with the shop - they should be embarrassed enough to just put a new one in for free.
Maybe the place that cleaned the radiator forgot to put the t-stat back in.