Hi all,

This is my first post here but as my good lady is now on her second Sporty, I suspect it won't be my last.

OK. The reason for this post is that Sportrak overheating seems to be a very common problem going by the number of posts/threads on this forum. It's a problem which has plagued Sporty No2 ever since we got it but is now fixed and I thought I would share my experiences (or should that be relief).

We acquired this Sporty last summer without a MOT. On the drive to the test station she started to overheat and the heater was called into use to keep the temperature sensible.

My first thought was the thermostat but in removing the housing one of the bolts sheared off (*!*#). I decided to let my local garage remove the remainder of the bolt and fit the new stat. Also had them fit a new water pump (and timing belt) at the same time. Result - still overheated.

Early this year it suffered a coolant loss from the engine water outlet where it joins the heater matrix flow pipe. Didn't fancy removing the distributor so back to the garage it went. Good news! The garage found that the engine water outlet was blocked on the side that feeds the radiator top hose. Testing showed a vast improvement but still a tendency to get hot.

Last week, Ali (the better half) took the Sporty on a drive from Norfolk to Essex - a much longer drive than it normally does. She got about 50 miles and it boiled over. The VERY VERY VERY nice RAC man diagnosed the radiator cap, replaced it and sent her on her way. When she came back a few days later, same problem! This time she managed to limp home over the course of several hours.

Now my wife had tried to cool the engine using the heater as before but could
get no heat from it so I suspected a circulation problem but decided to be thorough.

I removed the radiator top hose and the heater hose from next to the stat housing. Connected a hosepipe to the top hose. Result: Water gushed from heater hose and from the block where it had previously been connected. Conclusion: Cylinder block and top hose assy not plugged.

Removed stat and tested in hot water. Result: Stat opens and closes right on specifications. Conclusion: Stat fine.

I removed the radiator and checked it for flow, result: Water flowed out the bottom as fast as I could fill it. Then I laid the rad over at about 30 degrees and filled the rad with hot water via the bottom hose assy. When water started to flow out the top hose tube I felt the rad all over for temperature, result: Hot all over - no cool spots. Conclusion: Rad is fine.

Next I removed the water pump to see if the impellor blades were furred up. Clean as a whistle. Conclusion: Water pump is fine.

Right. Now I'm starting to get flummoxed. No restriction in flow. No mechanical failures I can find. Maybe it was just an airlock. Okay then, reassemble and test drive. Result: Same freakin problem although the heater is working really well now so I know the pump is circulating.

Starting to doubt myself a bit I question if the rad, although flowing well, is providing a resistance to flow just enough to make the water want to go through the heater matrix instead. Also, having read many of the threads here I'm starting to worry about the cylinder head. The lady loves the car so I'm authorised to start spending some money. As I'd never put a new cylinder head on an aging radiator, the radiator is less expensive and much less work - I decide to get the radiator recored first.

Express Radiators in Norwich did a great job and in a hurry for me as the car is needed (really needed) after the weekend, so a big thank you to those guys.

Refit the radiator (again), test drive. Result: Aarrrrrgh! Still overheating.

Now I'm in desperately deep denial about the cylinder head. I decide to remove the stat and test drive without one. Result: Temp guage bearly moves of the big 'C' on the left. Conclusion: The performance of the cooling system is capable of totally outstripping the engines ability to produce heat.

This posed a new question. If the stat was fine when tested, why does it appear to be blocking circulation through the radiator? Well another thread on here pointed out that a stat he got from a motor factor was not identical to the original and on buying one from a Daihatsu dealer his problem vanished. Now; we never got around to disposing of Sporty No1. We always toyed with the idea of using it purely for off road or as a donor vehicle. So last night I hatched me a plan and this morning I removed the stat from Sporty No1 for comparison. The shroud was in the same position which was the difference found in the other thread. I decided to heat test them both together. Result: Both open and close at the same time and by the same amount.

HOLD ON A COTTON PICKIN MO!

When the two stats are placed side by side the suspect one appears a little longer. Inverting one against the other confirms that from the sealing plate to the bottom, the original from Sporty No1. is about 4mm shorter.

Decide to fit stat from Sporty No.1 into Sporty No.2. Result: WhooHoo!!! Overheating problem has gone away.

Okay - if you made it this far I apologise for all the rambling and beating around the bush. So here's my point.

Although a cursory comparison may not show any difference, the devil is most certainly in the detail where these stats are concerned.

Daihatsu have really pulled a master stroke here. Traditionally, the stat is between the engine outlet and the rad and hence only measures the temperature ot the water LEAVING the engine. The setup we have on the Sporty measures the temp of the water ENTERING the engine (which is far more important) and only mixes the heater matrix return/bypass with as much cool water from the rad as is necessary to maintain optimum inlet temp. As such a relatviely cool bottom hose is not abnormal because the rad will be cooling water far faster than the stat demands it. The water therefore stays in the rad even longer and cools even further. This highlights just how important a good antifreeze is. In cooler weather the water in the radiator could easily be chilled below freezing causing the rad to split (ironically a rad in good condition may be at a greater risk than one on it's last legs).

Right. That's my sequel to War and Peace completed. A big thanks to all those whose threads gave me food for thought and I hope this will do the same for others.

Regards all,
SixFingersMike