I changed the radiator and thermostat on my 1988 acura legend but still overheats what can be causing the problem?

mixture of the radator fluid

This answer is possible but it is not correct and is a poor choice. There are a number of reasons why a car's engine overheats and the original question doesn't give enough information about the car and its overheating symptoms to deduce the answer to being a mixture of radiator fluid. It's not a good way to answer at all other than it being a guess.

The engine can overheat b/c the radiator is old and fill with rust/dus particles that clog it up and the engine as well as the hoses. It can overheats if there's a cooling fan and it's not being turned on at lower speed (bad relay switch or fan motor). It can overheat if it's low in coolant or that the water pump is not working well. It can overheat due to a bad/broken head gasket. It can overheat with trapped air in the cooling system that needs bleeding. When driving with AC on uphill for extended period of time, it can and prob. will overheat, etc. Many reasons for the overheat and to simply give the answer of mixing radiator is simply naive and dull. Do more research being being trigger happy with the fingers :)