Our pressure sensors are designed to be used with clean, dry air only. However, most of our customers ran their own tests to determine if the response of the sensor would be appropriated for their specific applications.
I personally ran a test with an MPXV5700AP directly exposed to car coolant @25°C and 100PSI, zero failure was detected for almost a month. See attached .xlsx for detailed information. The error of the sensor was calculated comparing the output of the sensor with a mechanical manometer, however this was only an approximation since the mechanical manometer was used as the "true pressure value".
In this kind of applications, we would recommend to use Parker O-lube silicone grease or DMS-T46 or T51. This type of grease is used by most of our customer without problems. In fact the basic recommendations are to use a silicone oil (or preferably grease) with high viscosity and high molecular weight. In this case the size of the molecules are big enough to limit the penetration of the grease inside our protective silicone gel which is over the die. In terms of contaminants, the silicon grease must be free of halogenures (Cl content < 50 ppm) to reduce the risk of bond pad corrosion. On the other hand, don't forget that whatever the material you will use, as soon as you put something on our gel you have a high probability to see some offset drift. This is coming from additional mechanical stress and/or gel swelling. The amount of gel and global mechanical design are usually also part of the offset drift.