My engine started overheating after installing a serpentine kit
Water Pumps and Cooling
If the engine ran fine before and runs hot after, work through how fast the water pump is turning first, then the cooling system itself.
Overview
Short Answer
Start with how fast the water pump is actually turning, not with the radiator. Underdrive pulleys slow the pump down considerably, and a belt that slips lets the pump slip with it. After that, confirm the thermostat is installed correctly and the system is fully bled, then look at whether your fans and radiator are up to the job.
Start with your pulley ratio
Underdrive pulleys will drastically slow down the water pump. If your kit went on with underdrive pulleys, the pump is turning slower than it was before and it moves less coolant at the same engine speed. That is the first thing to rule out.
Tell us which pulleys you ordered and we can tell you what ratio you are running. Our FAQ on underdrive pulleys covers what they change and what they cost you elsewhere.
Make sure the belt is not slipping
A belt that slips lets the water pump slip with it, so the pump never turns as fast as the ratio says it should. Check that the belt is properly tensioned and that the tensioner is sitting in its normal operating range rather than at the end of its travel.
Related: my tensioner is not sitting flush, my belt keeps coming off or throwing and my V-belt squeals under hard acceleration.
Thermostat and trapped air
If you installed one of our water pumps or thermostat housings, check two things before anything else:
The thermostat is installed correctly. Confirm it is in the right way round and fully seated in its recess.
The cooling system is fully bled. Air trapped in the system causes temperature spikes, and it is one of the most common reasons a fresh install runs hot.
Fans and radiator capacity
Once drive speed and air are ruled out, the question is whether the cooling package itself is big enough. Do you have adequate radiator fans, and is the radiator big enough for the engine you are running?
Air has to actually reach the radiator too. On a lot of builds the opening in the front bumper is the limit, so check that there is a clear path through the bumper to the radiator core once the car is moving. Our article on running hot with electric fans covers the CFM ratings we expect to see on a V8 build. If you are weighing a pump change as part of this, see mechanical vs electric water pump.
What to send us
If you are still stuck, email contact support with your order number and:
which pulleys you are running, and whether they are underdrive
when it runs hot, at idle, in traffic or at highway speed
your radiator, fans and thermostat rating
Still need help? Our tech support team can get you pointed in the right direction.
Contact Support