The soaring temperatures, the motoring organisation says, have coincided with spikes in the number of accidents and weather-related breakdowns.
And it is issuing drivers with advice to help them avoid running into problems when the mercury rises.
RAC research shows that as the heatwave took hold - sending temperatures in many parts surging well past the 30C mark - there was a 44% increase in the number of road accidents.
The number of drivers experiencing problems with their vehicles’ cooling systems, meanwhile, jumped by 23%.
Pete Williams, spokesman for RAC Traffic Watch, says the spate of accidents is a “major cause for concern”.
He adds: “There may be a wide variety of reasons for this, including the increased volumes of traffic and bright evening sunshine causing glare and a distraction for drivers but we expect the biggest factor can be attributed to driver fatigue, heat exhaustion and frustration.
“So it is really important to leave plenty of time for your journey, take breaks and keep well hydrated. This is particularly an issue when the hot weather makes getting a good night’s sleep a challenge.”
Breakdowns related to the weather have included cars overheating due to broken fans or other problems with their cooling systems.
Issues with air-conditioning systems, sunroofs and electric windows, meanwhile, have resulted in hot and bothered drivers asking the RAC for help.
Many, Mr Williams says, have been contacting the organisation to report pools of water beneath their cars.
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“This can be a particular cause for alarm,” he says. “But at times of high temperatures when the air con has been working overtime the unit freezes as it takes moisture out of the car and then when the car is parked this ice melts causing a puddle.
“The advice is to check whether this is simply odourless water or if it has coolant in and a clear smell and colour. If it is the former then there should be no need to worry.”
Drivers are urged to check oil, coolant and washer levels, as well as tyres, before embarking on journeys and to make sure they have enough refreshments for themselves and their passengers.