There is a minor addition to this post, it can be found here.

For most of the last year we have been unable to drive our car (a diesel PT Cruiser) for any length of time above 50mph, it took me until last Christmas to work out this was because the water pump (mechanical) wasn’t working (in my defence below 50 the car behaved perfectly, well unless you wanted to accelerate or go up a hill).

I finally found a guide describing how to change the water pump on the car, and it involved effectively removing the engine and some serious expense, hence I looked at alternatives. Davies Craig make a kit which would have done the job brilliantly but it was expensive, hence my solution, to build my own Electric Water Pump Kit from some smaller pumps off eBay.

The modification I have done is adding a D.I.Y (do-it-yourself) electric water pump system to our Diesel PT Cruiser CRD. When I say

The completed system

The completed system

I built my own I literally took three cheap 2nd hand eBay EWP’s (with 19mm tails) and hooked them up to the car along with a slightly modified programmable digital terrarium thermostat.

First of all I got the heater working. Last December we were traveiling in the car at sub-zero temperatures, which was incredibly unpleasant, so it was the priority job. Sadly I have no pictures.

To get the heater working I fitted a single small Bosch pump (2nd hand) with 19mm tails to the heater line where it runs under the air-box. This is easy enough to do and should take about a day, first remove the air box:

  • Disconnect the rubber hose which is held on with a jubilee clip
  • Take the top of the air box off
  • Disconnect the MAF sensor which is on a plug that has a tight locking mechanism but comes off fairly easily, or just put the whole assembly off to one side
  • Take out the air filter
  • Remove the front plastic grill of the car
  • Unbolt the metal cross brace that is above the plastic grill
  • Pull the cross brace up and slightly forward
  • You should now be able to remove the air box; pull up firmly and it will come out of its rubber mountings

Next you need to add the pump to the heater loop. Running just below the air box is the heater line from the engine to the heater, on it you can see the coolant pre-heater.  Drain the coolant system and disconnect the heater hose from the pre-heater. At the back of the engine bay the hose enters the heater matrix on a quick release fitting, this is very awkward to remove as it is pretty inaccessible, but the best way to do it is to push it slightly towards the rear of the engine bay, squeeze the two end plastic tabs with your fingers (the ones right at the back of the engine bay, not the side panels) and with some fiddling and cursing at the pain the hose will come off.

Fitting the pump is fairly easy. The old heater hose will accept 19mm silicone connections, so I cut into the hose (so still using the same ends) and used 19mm silicone pipe and fittings plus some odds and ends I had available to plumb the pump in. The bracket for the pump was part off-the-shelf generic Bosch pump bracket (from eBay) and a section of 90° bent pipe bolted to the plate that is fixed behind the air box. This might look terrible but it has lasted 7 months with no problems.

Powering the pump is a little involved, you will need to use a 12v supply that is switched from the ignition. I didn’t have the time to connect a relay to the 12v switched connection from the Engine Management Computer (and also didn’t want to stuff it up) so I ran a small wire from the back of the switched 12v accessory socket in the centre console and used that to switch a fused relay which controls the pump. Again this is a bit Heath Robinson but it has worked for the last 7 months (and I have spare fuses in the car just in case we blow the socket and the heater etc. stops working).

This mod makes the heater work, unless the thermostat opens, in which case the volume of fluid the pump has to move becomes too great (this was solved with the 2nd mod below) and as the flow slows down so does the heating effect. It also makes it awkward to get at the engine fuses and relays (but not impossible). Of course it doesn’t fix the whole overheating problem, but once it was in and I had an appreciation of what would cool the car I knew I had to simply add some more pumps.

We now fast forward 7 months, 7 months of madness at work and no free time, to the next weekend I had free to work on the car (a few weekends ago in fact) when I finally added the two extra pumps.

To do this I needed to get the pumps into the lower radiator hose (38mm) to push coolant back up into the old water pump. I found two more small pumps with 19mm hose connections (38mm pumps which would fit straight into the existing hoses are still very expensive) and looked everywhere for an adaptor that would have a 38mm inlet and two 19mm outlets. I didn’t find one and therefore had to make my own.

I bought two 38mm alloy silicone hose connectors, plus two plastic 19mm straight and 2 plastic 19mm 90º bends. To get the 19mm plastic fittings to fit into the 38mm connectors I had to flatten the end of the alloy connector slightly. After some adjustment the plastic fittings sat snug in the alloy connectors. Next I used JB Weld to close up all the gaps.

The pumps are controlled from a digital programmable thermostat. I chose a Chinese made thermostat off eBay designed for a terrarium. This thermostat was a normally closed unit which went open circuit when the threshold temperature was reached, a simple wiring change took the control signal off another relay (on PCB) contact. As the solder joint wasn’t mechanically strong enough for long term use I passed the control cable through the board several times so that it would take the strain off the joint.

The sensor for the controller is a thermistor which I intended to install within the thermostat (tucked into the edge of the top hose). In the end I passed it in the same way into the top hose of the radiator (easier to get to). Here I was measuring it (using the old thermostat from the car – it was one of the things I changed in 2011 trying to get the heating/ cooling to work again – please note I still have a mechanical thermostat in the car, just not this one) so I could add some protection to the cable, which was heat shrink, with silicone squeezed into it and then once that had set I activated the shrink to make a solid collar around the end (the cable was only rated for 103°C). The collar also provided some mechanical protection to the cable as it passed under the jubilee clip.

The pumps I used were two identical Bosch units I bought 2nd hand off eBay. Sadly they came off two different brands of cars, so they had different plug connectors and as I’d ordered the normal Bosch ones I was a bit stuck. In the end a solder-helping-hand and a jar or peanut butter helped me to solder new wires onto the plug terminals, once I’d tested these with a 12v supply (surprisingly these pumps are very low current) I sealed the ends with JB Weld (which is also an electrical insulator).

Next I installed the digital thermostat in the car. This was fairly easy, I placed it on the RH (drivers side over here) side at the back of the engine compartment, high up on the bulkhead (behind the bulkhead at this point is a large space where the windscreen wiper motor sits, all you have to be careful of are the cables for the motors). I put in a relay holder with it and fitted a relay that is controlled by the ignition to turn the thermostat on or off.

The control feed for the relay I took off my earlier relay for the heater pump, the permanent live side of the relay is fed from a new fuse box I added, the live coming from the jump-start point on the opposite side of the engine bay (in the diesel version of the PT Cruiser the actual battery is under the passenger seat).

The live feed, pump control signal wire and ignition feed are all routed through the space below the windscreen where the wiper motors and washer bottle are (this is tidier than trying to run them across the engine bay).

The sensor wires (which are set at 1m long for accuracy in the factory, and just fit) are run out to the edge of the bonnet lip via a small hole I drilled, and then come back in just above the radiator via the bolt-on piece of body work that holds the top of the radiator in place. Again this is to protect the wires.

The earth for the whole lot is just connected to one of the screws that bolts the housing back to the bulkhead.

The relay that controls the pumps is next to the jump-start point. A 4mm copper cable runs from the jump-start point, to a 15A fuse in the new fuse bay to the relay and then under the air box to the new pump position. The relay is activated via the pump control signal wire that comes from the digital thermostat.

Only one of the pumps came with a bracket, I modified this so it would fit to the LH side of the radiator (passenger side in UK) and as the pumps are small and light I lashed them together on this one bracket. I used amalgamating tape to build up a ridge on the pump that has no rubber guards to make the pumps sit evenly together, and then my Dad found an old exhaust mount as an additional spacer and used a doubled-up jubilee clip to secure them. The way they are arranged when on the car means that they are supported at the far end by the air-inlet hose to the intercooler (which on the CRD PT Cruiser is a stock part and mounted under the radiator), and partly also by the water hoses they feed.

The final step was to plumb all this into the car. I drained the system of coolant and added the sensor into the top hose. I also added some silicone gasket sealant around the hose to stop leaks around the wire where it entered (in these pictures you can see a bleed point which is not part of a normal PT Cruiser, I will cover this in another post, please ignore it for now).

Next I cut the bottom radiator hose. On the CRD PT Cruiser you cannot get at the other end of this hose, so if doing what I did be very careful and make sure you don’t cut too high up.  I disposed of the old bottom end of the hose (where it exits the radiator) and replaced this with a 90° 38mm hose I got from another car, this is to make sure that the hoses that run from the base of the radiator to the pumps fit between the air-inlet pipes for the intercooler and the radiator. I added the two 38mm to 19mm adaptors I made, fitted and wired the pumps, connected it all up with 19mm silicone hose and fittings (plus some amalgamating tape and jubilee clips in places) and got ready to refill and test it all (the photos below were taken after the first test, hence the mud splashes etc).

When I first refilled the system I used plain water, just in-case the whole thing leaked like a sieve or blew a hose. There was one small leak after the first fill at the point the wires for the thermistor (digital thermostat sensor) entered the top hose, which was fixed with some silicone sealant (delivered after fully draining the system of the clean water for the first time).

Once that had set I refilled the system with plain water and went for a drive, which included a 30 minute 70mph stretch on a nearby dual carriageway. Normally that would have had the car overheating in moments, but the temperature remained stable at the mid range the whole time (I set the thermostat for 90°C as the mechanical thermostat does not open until it reaches about 80°C, I later changed this to 95°C to reduce the number of times the pumps come on and hence reduce wear on the pumps and relays). I assumed at the time that on a long journey the car still might overheat.

I got home, checked the system for leaks (none) and bled the system, which is when I broke the flange off the bleed point on the top of the radiator (thankfully it was still closed). As I have said many times I will cover the new bleed point in another post, but for now it involved the draining of the system again, and the next day refilling it with plain water, testing it again for leaks, and then finally draining it one more time and adding the proper anti-freeze.

The final test was the drive home from my parents (who have a garage with a pit), which was a 2 hour motorway speed journey. I started off taking it easy, no issues, so I got a little faster, still no issues, and then after 20 minutes I opened it all the way up and kept up with traffic in the middle and outside lanes.

The car did not overheat.

Not once.

It never even got above the mid point on the temp gauge.

I was needless to say very happy, and after a year of being the slowest thing on the road not a little alarmed at how much I had forgotten about lane changing and overtaking.

The car behaved itself for the next week or so (still never going above the mid point temperature wise), until when driving down to Peppa Pig World (another 2 hour journey) it suddenly overheated whilst I was driving at 70mph in the middle lane. It did not just overheat slightly, it went mad, the needle shot up well above the ‘H’ on the dial (the top of the red segment, the hottest I’d seen it before, being some 10mm below this), we had to pull over to the hard shoulder with the over-temp alarm going nuts.

Thankfully it was just the blade fuse I’d fitted was loose, easily fixed by swapping for another one of a different brand I happened to have in the car which had slightly thicker blades. Luckily the hoses all held and we had no leaks (at the time, I later discovered that it had compromised the new bleed point).

So all in all I am very pleased with the performance of my bodged-up home made electric water pump cooling system :-)