The following is a list of the 10 most frequently asked questions that we receive at Stewart Components.

If your question is not answered here please browse through our Tech Info Section and our Q&A Forum. If you still cannot find the answers you need, post a question to the Q&A Forum and someone will try to help you answer your questions.


Q1. Will the Stewart Hi-Flow water pump reduce my cooling temperature?
A1. Yes. The water pump is the heart of the cooling system and flow should always be maximized to reduce temperatures.

Q2. Which pump is best for my application (cast iron or aluminum)?
A2. Both are Hi-Flow and will work well although the aluminum version is available in a hand polished finish.

Q3. Do I need to run a thermostat and what is the best kind?
A3. Most street driven vehicles should use a thermostat and we recommend the Stewart/Robert Shaw hi-performance one that we modify for better cooling.

Q4. What about my pulley set-up (what ratio do I need)?
A4. For STREET applications, the water pump speed must at least match the crankshaft RPM, to a maximum of 10% faster than the crankshaft speed.

Q5. My engine runs cool enough out on the highway but heats up at slow driving or at idle. What is most likely the problem?
A5. Most stock or OEM pumps are built to meet standard performance requirements and at low RPMs the flow is reduced, the Stewart Hi-Flow water pump is designed to produce increased flow at idle as well as higher RPMs.

Q6. What is the best coolant to use?
A6. If freezing is not a concern we recommend water with a corrosion inhibitor. If freezing is a concern, use the proper amount of antifreeze required for your climate.

Q7. Which radiator is recommended (aluminum or copper)?
A7. We strongly recommend aluminum radiators. They dissipate heat more efficiently than copper brass.

Q8. What size radiator should I use for my application?
A8. We recommend using the largest (in surface area) that will fit into your vehicle.

Q9. What would be the correct pressure cap rating to use?
A9. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept.

Q10. Which cooling fan do you recommend (electric or mechanical)?
A10. Electric fans now outperform mechanical fans in nearly every application.