Just finished my Haynes roadster build (Yay!) using 1.8L Sierra CVH engine. All working fine except engine overheats. The engine starts easily and runs smoothly,l but as engine temp rises the radiator circuit is not filling. During the build I fitted a new thermostat and I'm pretty sure i fitted it correctly and it was the correct one, but I presume the thermostat is the issue. In the Sierra Haynes manual it says that an airlock could cause this problem.

Sometime back I bought a new water pump, so I am now planning to drain coolant system, check/change thermostat and replace water pump. However before I do all that I wonder if you clever guys have advice on how I can confirm what is causing the problem and any simple fix that will save me having to take front of the engine off again?

Thanks

If you think it's the thermostat, then remove the thermostat and see if the problem goes away. Running without a thermostat won't cause any problems in the short term.



You can test thermostats in a pan of water, if you have a thermometer.

You can also get some idea of what's going on by feeling the water hoses and radiator as the engine warms up, to see how far the heat is circulating.

quote:

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Originally posted by Sam_68
If you think it's the thermostat, then remove the thermostat and see if the problem goes away. Running without a thermostat won't cause any problems in the short term.



You can test thermostats in a pan of water, if you have a thermometer.

You can also get some idea of what's going on by feeling the water hoses and radiator as the engine warms up, to see how far the heat is circulating.

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As above is easiest, run with no thermo.

But also worth checking your coolant flow is correct, have you got a diagram showing coolant flow for your engine?

Also, check you've got the correct circulation. The header tank/expansion bottle/tank should fill into the bottom hose (between the water pump and bottom of the radiator). The return hose to the header tank should feed off of the highest hose on the system (usually the top hose or a specific feed pipe, NOT the old heater circuit hoses). The heater circuit hoses should only join up to each other, whether you have a heater or not. Finally, the highest points on your system should ideally have some sort of air bleed on them to release trapped air to stop air locks in the system (these bleed hoses, if multiple bleeds, can all be all be joined together and fed back to the header tank).

Also, remember, water likes to flow down hill and air always likes to flow up hill in water. So try and avoid hose positionings that SOME of the manufacturers seem to think was Ok (like the rover 200/400 top hose of the radiator went down hill off the radiator, under something then back up to the engine connection, DOH).

I hope this all makes sense.

drilling a small hole in the thermostat ring can help prevent airlocks. Seems not all are supplied with a hole (they used to, with a jiggle pin fitted)

Could be the 'stat... but could be other things. Have you got a diagram or pictures of how it's plumbed.

What do you mean by "radiator circuit not filling"? It shoud be constantly full, so I assume you mean the water isn't circulating.

It could also be as simple as the system needs bleeding, when the temp is rising the temp gauge needle should drop around 80/90 degs when the stat opens (gauges are never really accurate readings)

Also feel the pipe work from the stat housing to rad as this should be hot when the stat opens, and feel the top of the rad as this is where the air lock will end up.

Height of rad or expansion bottle is paramount, expansion bottle or header tank should be above cylinder head water outlet.

Rad fan thermo switch is also important and should kick in around 100 on the gauge at least.

Another point when warming up keep revs up a bit 2000rpm now and then as this will spin the water pump up and move the water around quicker.

Lots to think about but information or pictures of your plumbing set up would help also.

When I finished mine it was overheating badly with its polo radiator and cheap universal 12v fan. I brought an expensive aluminium thick core radiator and a decent Spall fan. The fan was the one that made all the difference and it was a lot cheaper.

OK from my understanding of your original post it sound like the thermostat isn't opening probably because your car has had the plumbing for the heater blocked off The water circulation through is continuous in donor even when the heater is set cold, it is vital this is not blocked off as it provides flow that by-passes the radiator and the thermostat.

If you don't provided by-pass flow the thermostat won't get hot enough to open until the coolant is boiling hot.

Drilling the thermostat will help but it won't provide enough by-pass to keep the bottom of the engine at an even temperature.


More to follow

[Edited on 26/8/15 by britishtrident]

The by-pass hose back to the small inlet on the water pump (or it can be Tee'd into the bottom hose) the water pump circulates water through the block and head continuous, this prevents localised boiling and warms the bottom of the cylinders and crankcase (and oil) temperature.

Even worse is running without a thermostat as the the engine will run below design temperature and oil temperature will allow acid condensation in the oil. On most engines it will also cause problems passing an emission test.

Testing a thermostat in a pan of almost boiling water is possible but it isn't easy as it might seem, the rated temperature of the thermostat is the temperature at which it starts to open. on for example an 88c thermostat the water needs to be heated to about 92+ c before it opens enough to be noticeable.

Thanks for all your advice. I have drawn the coolant circuit on a powerpoint slide.

I am pretty comfortable that the main circuit runs from bottom of radiator to water pump through engine and out the inlet manifold to thermostat and back to top of radiator. Before the thermostat opens water will run from a 'T' junction on the bottom radiator hose up to the automatic choke bimetallic strip housing and then on to thermostat housing. So presumably before thermostat opens water runs around engine and automatic choke circuit only. When thermostat (should) opens the water runs to radiator top hose and back through bottom hose. The expansion tank is the highest point and has an overflow pipe to the top from the thermostat housing and a large return to bottom radiator hose. I am using a Renault clio radiator and it has a third port at the top and I have a T piece from the top radiator hose into this port.

At present engine overheats and the top radiator and bottom radiator hoses are not getting hot. Whereas the circuit through automatic choke are heating up.

Please advise how I upload the image of the circuit and I will attach the drawing.

Thanks

is the temp gauge compatable with the sender unit

yes all came from the same car.

Some gauges, my Smiths ones for instance, run off 9.9 to 10 volts.

Both my fuel and temp gauges have a reduced feed from a voltage transformer.

They were often an oblong metal case about the size of a twin Lego block and mounted on the back of the speedo.
Thanks to a "very nice man" from this site I now have an electronic version.

I have a flat rad cap on the rad and a air bleed from the rad overflow to the header tank, and a pressure rad cap
on the headed tank itself. I also fitted a lower temp fan switch.

Paul G

It turns out the temperature sender was the problem. I had bought a new one on the internet but had the wrong one. I got the official Ford part (for £45!!!!) and now it works and when water gets up to temp the thermostat diverts coolant to the radiator. Success. Ya Hay!

Now the radiator switch is not working, so fan won't come on. sooooooo frustrating! as these are the last bits and I'm having problems with every step. Got a new radiator switch but the old one is so welded in place I can't get it off. So I bought a billet aluminium insert from Car Builders and put it into the pipe further along and wired it all up.

The coolant has to be quite close to 100c before the fan switches in, if your system is properly sealed with a pressure capthe coolant boiling point is just under 120c

As above; means a very long time on idle/light load before the fan kicks in (20minutes on my CVH, with heater!!)...

Dan

I checked switch with voltmeter and it was not closed when engine temp was just in Red zone on meter, so I have fitted new aluminium section into coolant tubing with and new Ford radiator switch and now it works. Fan comes on when temp gauge is in upper two thirds of range, so I think this confirms my original diagnosis. Finished and now double checking all my IVA manual requirements and next step is to book my test (EEK!).

Thanks for all your advice.

If you want an easy way to check actual temps, Aldi have IR thermometers in at the moment for £15