Electric water pump temperature sensing

[Ben Wilson]

For various reasons, I'm thinking about fitting an EWP to my car.

I've been thinking about the temperature sensing part of it. While the coolant temperature is important, logically, if the coolant is flowing too fast, the coolant temperature will remain low while the engine gets hotter.

Would it be more logical to mount the temperature sensor on the head than in the coolant?

[tim510]

the davies craig controller is good, however i found then when set to the 'coolest' setting ie the most voltage it would only ever give the pump 9.5-10.5 volts instead of the 13.5 onhand..

with the help of a mate we rigged up an overide relay and switch to give the pump full voltage when i think its hot....

when the car was stationary with the thermos blowing, the engine temp was around 90c, and the pump voltage was around 10v, we overrode the controller and gave the pump 13.5v's, the temperature at idle dropped in minutes to around 75c......

the controller is very good at getting the motor up onto temperature well

[Ben Wilson]

Thanks, it would be fairly easy to hook up a Jaycar temp switch for that I suppose.

[bazeng]

doesn't the controller come with a relay already?

i've installed mine and it had one..

the source voltage is from a 12v source..

[tim510]

i rigged up an over ride switch with a relay....

so the pump either gets its regulated power from the controller

or it get 13.5v's from the cars +tive circuit.... not overly techincal, but i believe it will work well..

i think that what i think is 'hot' really isn't...i don't like seeing anything much over 90c, where as other cars run into the 100's and thats fine...

the idea behind what i wired up was to get it onto temperature and then run it flat out inorder to maintain that temp....

its also essential with the EWP's to bleed the cooling system exceptionally well, this took quite some time on my application but once done u could notice what a difference it made.

[bazeng]

any tips on bleeding the system?

or even starting the pump for the first time dry?..

[Ben Wilson]

I got mine last night, the instructions seem to explain the bleeding procedure fairly well.

[bazeng]

im just lazy..
also just wanted some first hand experience..
i know some manuals can be dodgy

[tim510]

i just shoved the hose down there and filled the system up and ran it...1 or 2 seconds with no water would not hurt it i reckon

[bazeng]

update:

u can wire in resistors into the sensor wires (parrallel) to reduce the tempurates

eg,
pulse at 60 degree's C
fulltime at 90 degree's C

with resisitor
pulse at 50 degree's C
fulltime at 80 degree's C

and so on, the more resistors, the lower the temps get..

i've had to wire in 2 resistors to overcome the hot at traffic lights problem,
it keeps my motor at about 80 0 90 degree's C at the moment.

[THE ASH]

What did you guys do with your mechanical pumps? just disconnect them or empty the housings? These EWPs run without thermostats, yeah?

[bigmuz]

(this post says in a nice way that you are all mental for using ewps in anything but a dedicated race car, and even then only in a drag car.)

[edo]

I agree with muz, but he is nicer.

cept tim...cause I know he couldnt fit a real water pump

[jmac]

Here's the 'rub' if you will. The role of the thermostat in a 'normal' cooling system is twofold. Obviously one is to regulate coolant temp. Duh. But the _other_ thing, is to actually deliberately present a certain degree of restriction _at a particular point_ in the circuit. which is why if you remove a thermostat, you should run a restrictor plate of sorts (unless the thermostat housing is so dodgy it functions like that as is).

So why this restriction? Simple. The water pump is (or should be) mechanically driven, so apart from the increased pressure possible via the radiator cap, whlist the pump is spinning, against that restriction, it will help prevent cavitation, and air pockets developing BUT it will also raise the pressure of the water in the water jackets of the block itself. This raises the potential boiling point of the water even more, and it also tends to improve the effectiveness with which it can conduct heat from the block/head.

What does this all mean for the electric pump? Well, if you try and regulate the coolant temperature via pump speed, then you will basically totally negate any possible transient increase in coolant pressure in the block. it's far less efficient at conducting heat away and can invite air pocket formation (or even steam pocket) and then you have a potential situation where the block is getting hotter, but the coolant isn't conducting it away as effectively, so it 'thinks' the coolant temp is low, and might even (shock horror) slow the pump even more.

On top of all that, most electric water pumps (or perhaps some) have adequate flow rates in theory to provide adequate circulation for peak requirements. But they tend to ALL fall down and pump fuck all if there's any restriction/load/resistance to flow. Basically they just can't generally function as mechanical pumps can.

On certain drag cars, the pumps were used on purpose not because of their advantages in any of these areas. But simply because after the burnout and moving in to stage, the engine would still tend to be below optimal temp, and being able to cut the electric pump in the staging area meants they'd get more heat into the engine, and it'd be more responsive off the line and in the lower gears (early pro-stock I guess for example). It's hardly a big deal, but around 15 years ago there was a torana with a big boost nissan engine (for it's day) running fairly obscenely quick 1/4miles. Somebody actually got wind of the fact they were doing this during staging (and running minimal radiator capacity for every weight reduction they could find). and they deliberately fucked around during staging to delay it as long as they practically could. the engine ended blowing the head gasket at around 1000ft and the 'pricks' got the win (some sort of grudge race, as they weren't similarly specced cars, just similarly performing.

Point of all that? Please don't do it, it'll almost certainly end in misery.

John McKenzie

[bazeng]

ash, with the water pump i removed the turbine and pulley / bearings etc etc.. i'm just using the case with a welsh plug sealing it....