COOLANT SYSTEM TIPS & TRICKS
Cooling System Tips and Tricks
There are a number of issues people commonly face regarding the cooling system. This short article is not about specific brands or components, but about general practices and troubleshooting methods that will help you make the most of whatever you choose and aboid these problems from the start. I don't have a lot of pictures to share here, but I'll add more in the future as I get them.
Mechanical water pumps actually work quite well. With a 1000 hp engine driving them to high rpm, they're going to move water one way or another. And they can build pressure in the block/head, which is a good thing for raising the local boiling point in those areas where it really counts. If you stick with the mechanical DSM water pump there's not much to be done with it and you'll focus on radiators and other parts. But, there are a number of good reasons to switch to an electric water pump, and many of us have done so. Being able to quickly cool the motor between race rounds for example.
The rated flow is not critical in my experience. More water flow is always better, but if you install your rated 55 GPM pump in a system that only allows 20 GPM water flow, you're not getting the flow you think you are. I recommend focusing instead on creating a high flow complete setup, and choose the best pump you can afford. If that's a 30 GPM pump, but you make the most of it, odds are it will work very well for you. To look at this from another angle, I had a restrictive cooling system that caused problems for me. Upgrading my 35 GPM pump to a 55 GPM pump made no discernible difference whatsoever with the problems I had. Make a note of the rated current draw of the pump you choose though, you'll need this later. If that is not supplied, ask the manufacturer for it.
Install the pump as low as possible in the system to gravity feed it. The lower the pump is, the lower the water level can be and the pump will still move water. Additionally, mounting the pump at a slight angle to point the outlet upward can help purge the air that is normally trapped in the internal chambers of the pump housing. Take a good look at your pump and try to give it what it would want to easily purge air.
How (or when) you activate the pump is also important. In my experience, don't try to leave it off until the engine warms up, or any similar strategies. If my engine is turning, I want my pump running, plain and simple. Water needs to be moving past the ECT sensor in order for it to read something close to actual head temperature. It's easy to cause issues here, for no real benefit. With a temperature controlled fan, there is no need to try to control the pump in the same way. If you insist on PWMing the pump or otherwise controlling its speed, just be sure that there is always some small flow at all times as a minimum. In my case, with the stock DSM ECU, the stock fuel pump output is a great trigger for the water pump's relay.
Line size is important, and bigger is better. In some cases however, like my own car, I'm limited to -12 lines. These are small for cooling system use, but if you maximize flow in other critical areas this has been shown to work just fine. Moral of the story, go with the biggest lines you can fit (-16 is typical, even -20 is used in some cases). Use fittings with nice, smooth bends, and avoid hard 90 type fittings unless you have absolutely no choice (I have to use these in some spots for clearance reasons that I can't get around. It's not ideal). And in some cases, special fittings are required. My current water pump for example requires special inlet/outlet fittings from the same manufacturer to avoid creating a restriction inside the pump ports.The lines on the inlet side of the pump are the most important. Centrifugal water pumps are like any other dynamic pump, it's not going to tolerate inlet restriction well and cavitation will absolutely kill water flow. In my case, I was able to easily fit a -16 line from my radiator end tank to my pump inlet, and that's a good thing. My -12 lines on the pressure side do not appear to be a problem.
In addition to the obvious problems with having air behind hot spots like the combustion chamber in the head's water jacket, air in the system is also an obvious source of pump cavitation on the pump inlet. Come up with ways to remove entrained air in the system. I use an inline can at the head outlet, highest point in my system, that is designed to trap air bubbles going by and not pass them on to the rest of the system. Doing this at the radiator cap lets the system push the collected air out first as the water expands with temperature. Avoid building air traps into the system. High points in lines or for example a high mounted water pump with inlet and outlet lines running downward will trap air that can be hard (or impossible) to purge out of the system. If this type of situation can not be avoided, build an air bleed into it. That can be either passive (you have to open a bleeder port to let the air out) or active (bleed line run uphill to high mounted surge tank/air separator). Vacuum filling the system can eliminate the air, but relying on that can be problematic if you have to fill the system at the track for example. I use a vacuum filler myself whenever I can, but it's best to build the system to effectively purge its own air, if at all possible.
I've since ditched the pressurized water caps entirely and gone to a completely closed threaded cap, with a pressure relief valve elsewhere in the system, but that's a long story for another tech article.
In short, air does not store/move heat nearly as well as water, and water pumps can't pump it for shit. Keep air out of the system at all costs.
Pictures of air separator on my car, and Kait's 2g:
Most people have seen intercoolers installed with no ambient air flow provided (behind a bumper, laid flat, etc) and understand that the IC acts as a heat sink and works adequately in this way for a short drag pass. Radiators are not unlike intercoolers in this way. Lightweight radiators designed to quickly transfer heat to moving ambient air work well, but in a drag racing application a heavy radiator with low air flow can store enough heat as a heat sink to do the job for a drag pass. Just like intercoolers. And similarly, you want very low pressure drop, in this case, as little restriction as possible to the flowing water in the system. Core design, end tank design, and water inlet/outlet situation are all factors.
To use my car as an example, I swapped out a “normal” radiator with a large high power fan for a much smaller, but much heavier, bar and plate heat exchanger with 2 small 7 inch fans. This core is 26x7x3.5 thick. It looks just like a bar and plate intercooler core. It came as a dual pass setup, with inlet and outlet on the same side, using the opposite end tank to reverse the water flow direction. This did not work well at all. At first glance someone will say that's because it's too small, or because it's not actually a radiator, etc. Turns out it works fine, with some mods to increase it's water flow dramatically. More on this in a bit.
Whatever you choose for a radiator, make sure it's either got enough heat transfer to keep up with demands at WOT, or enough heat sink mass to store the heat to be released later on after the pass. And be sure it does not restrict water flow, that absolutely kills cooling system performance.
If you use a traditional radiator pressure cap, I recommend a good high pressure locking cap. We run straight water in race cars, and raising the pressure of that water is the only way we have to raise its boiling point above 212F. Put that cap on the suction side of the pump! Otherwise, any pressure the pump might create downstream works against the cap, reducing it's pressure rating. On the suction side of the pump, the pump works with the cap and increases it's pressure capacity a little bit. This has been a major factor for me in previous setups and something I watch closely now. In a small closed loop like a race car's cooling system, and considering the largely incompressible nature of water, there is not much distinction between pump inlet and pump outlet, unfortunately. But you can generally expect the radiator and engine to be the main restrictions to water flow. Between those items and the pump's inlet is effectively the suction side.
Any restriction to water flow in the system is going to cause problems. Moving a lot of heat requires moving a lot of water. The job of the water is to move heat from critical areas, like the back side of the combustion chamber, to the radiator to be stored/rejected to the atmosphere. More water flow can move more heat. If there is not enough water flow, the water in the head can overheat, vaporize, and then you've got problems. Overheating, exhaust valve seats shifting, knock, plugs overheating, etc.
Water pumps are dynamic/centrifugal. They do not build pressure well downstream (to try to overcome downstream restriction), and they do not tolerate inlet restriction well at all (cavitation). Most people these days are familiar with this regarding intercooler water pumps. It's no different for the engine's water pump. Easy, high water flow performans significantly better.
Using my car as an example again, I had that dual pass 26x7x3.5 heat exchanger, with inlet and outlet on the same end. Water would go in the inlet, use half the core height to traverse the core, use the far side end tank to reach the other half of the core height, and return to the outlet port, which then went to the water pump. The water pump feeds the head, and the head returned water to the radiator, to complete the system.
Pic of core as received:
I had this “radiator” modified to convert it to single pass. Both of the very slim end tanks were cut off and replaced with larger end tanks, 2-3 inches deep. The divider was removed, and an inlet fitting added at one end and an outlet fitting added at the other end. Single pass. The flow area of the core is now doubled. The larger tanks also facilitated upgrading the fittings to -16 bungs, rather than the -12 bungs (half inch NPT) that it came with. The thicker tanks also allow water to more easily reach the core rows at the extremities, rather than force most of the water to use the few rows directly inline with the stock water fittings (this was a HUGE deal on my air-water intercooler...).
Pic of core modified:
Restriction to water flow can be a pain in the ass to measure. You could simply flow water from one bucket to another and time it to determine flow, but that's not quite the same as it would be in it's completed orientation and closed loop. An easier and more effective way to measure it in my opinion is to simply measure the current draw of the water pump. In my example here, the restrictive setup only drew about 2 amps, on a pump rated to draw 11 amps. That was an obvious sign of trouble. After the modifications to increase water flow, the current draw tripled to 6-7 amps. Still well under what it's capable of, but we can be sure the pump is now moving a lot more water. The remaining restriction is likely in the head itself, and in the few remaining bits of -12 line and tight low profile -12 90* fittings I'm still forced to use. I use my Power Probe Hook (https://www.powerprobe.com/the-hook ), which can provide up to around 60 amps to devices and measure the current draw quickly and easily. But other methods will work as well.
It's good to know the rated current draw of the pump. I would also suggest hooking up an inlet and outlet line in the size you intend to use and measuring current draw while it moves water from one bucket to another (gravity feed the pump inlet if at all possible). This should give an idea of the “best case” current draw you can expect once installed. With current draw significantly below that value, you can start to look for the cause.
To complete the story, the car, once over ~1000 whp, would regularly overheat and push a bunch of water out of the system on a pass. There was always some suspicion the head gasket was allowing combustion pressure to push the water out (rightly so), but there was no good way to be sure which was happening. And on random passes it would work fine, leading one to believe that the system was capable of doing what it should and was “ok.” At some point I upgraded the 35 GPM pump to a 55 GPM pump, and that had absolutely no effect. Checking the current draw of the new pump on a whim I found it quite low at 2.x amps. After making the above mentioned mods that tripled that number, the system started working as it should. I can now warm the car up in the pits, drive it up to the staging lanes, make a 7.9x pass, and drive it back to the pits, all before the fan ever kicks on at 180F. It's still less than a gallon of water total system capacity, and using an odd bar and plate heat exchanger, but working extremely well. Same components as before, just more flow.
I think most people would say they already know that water flow rate is important. But determining what it is and working to improve it is a little more obscure for most. Since finding this all out the hard way on my own car, I've applied these learnings to other cars with great results. Hopefully it helps others sort their junk out.