The answer is that most electric pumps do not have the capacity to serve in ALL driving conditions that you may face. Your dependency on heat removal is based on flow. When you are in need of power at speed or going up hills, towing etc, the hp generated is more and thus the heat generated is more. Ya gotta get rid of it
While at idle and depending on how much shear cooling area you have in your radiator and how much airflow you have thru it, you do not need the flow from your water pump you need at cruising down the road. The combination of airflow and coolant flow at cruising speeds increase the efficiency of the radiator dramatically! Most quality electric water pumps of about 55 gpm (forget anything less!!!!) are great for idle and slow speed cruising because they actually provide more flow at low speeds than all stock mechanical pumps and even high performance pumps. Most stock water pumps only provide about 10gpm at idle! High performance models are more like 18gpm at idle. You can see why a 55 gpm electric would be better.
But, even Stewart Components, a world leader in both mechanical and electric water pumps technology says this about their inline "booster" electric pumps.
"Stewart's inline booster pump is intended for vehicles that experience overheating problems in low RPM situations. Since mechanical water pump speed is directly linked to engine speed, overheating becomes a major problem in situations such as parades, cruises, and stop-and-go traffic. The inline booster pump solves this problem by working in conjunction with the mechanical pump to create constant added flow to the engine block; the pump has been proven to increase flow by more than 300% at idle".
In other words they know and recommend that these pumps NOT be used by themselves! Yeah,... I know that other companies will tell you differently, but they WANT to sell you their specific products.
Simply put, the more flow the more BTUS get moved! So, depending on how much power you are using at certain rpms will determine whether or not you NEED the extra flow. I think in the poster's case here is that the flow is simply not enough. I am suspect that if it's a "cheapo" device, that it is less than 55 gpm?
High performance mechanical pumps can provide upwards of 65 to 75 gpm depending on crusing rpms.
I know guys here in Atlanta that put high end, quality electric pumps on because they simplify and make the engine compartment look neater etc. I agree..looks great! They work fine in and around town idling and slow speed. But, on their trips to the Smokies it did not take too much of an uphill grade to make them start to overheat? They wondered why and the simple answer was they were using more power and needed more flow as a result. I had a friend that attached a small trailor to his street rod with an electric pump and he could only drive 50mph with it or he would start to overheat at higher speeds utilizing more hp!
So, to answer your question, if you have a unit that is NOT producing at least 55 gpm that's the problem. You might be able to get by on an electric model of higher capacity. But, a safe bet is to go to the high performance water pumps such as a TuffStuff or Stewarts. They are very inexpensive and quality stuff!
