Sigma 125 self build. Cooling issue

[bbkRob]

Just about finished the build so I thought I would take the car for a trundle round the yard. When I did the start up a couple of weeks ago all seemed OK with the cooling system. When I took it out in the yard yesterday afternoon it got quite hot, sitting just below the red. Here are the symptoms.

 

Top hose and top of radiator are hot (but not scalding hot), bottom hose and bottom of radiator are cold. Fan comes on but cuts as soon as the engine stops but ignition is still on. When I turned the heater on the pipes warmed up and the heater blew hot air. Small return pipe to expansion bottle has water flowing.

 

From this I conclude that the pump is working. The system has a capacity of 5.1L and it has 5L of coolant in and the level when cold is just below minimum in the expansion bottle so if there is an air pocket its not a very big one.

 

Its off to Caterham for the post build checks and IVA on Tuesday so I would like to at least understand the problem before then.

[elie boone]

Can u take the temp with a infra red ? so that u have a better vieuw about the real temp of the engine, it could be that the gauge or the sender are faulty.

[bbkRob]

I have an infra red temp probe but I can't find it. I have nasty feeling it got left at a race track last year. I use it to check track temperature and I think someone took it to get a reading and it never came back. I did wonder about the accuracy of the reading but the fan kicks in as the needle gets to the mark between 80 and 120 so that would be about right.

[nickhi]

bbkRob, I have almost completed my build and have run the engine for the first time. Not sure if my cooling system is right though. I ran till about 60 deg on the gauge and could see coolant flowing into the expansion bottle so guess pump is working however Radiator is stone cold (both Top and Bottom hoses), I was kind of assuming it would feel warm. Was just wondering what you found when running for the first time. I have 5L of coolant in and have seen no leaks.

[The Pikey]

at 60 deg your stat is still closed and the water is only running round the bypass route so your rad will be cold. Run it to above 80 and you should find the rad gets warm.

 

Jason

[bbkRob]

The 5L of coolant isn't enough! Book says 5.1L is the capacity but I think its a bit more.

 

Mine has a heater and I'm thinking 6L.

 

The radiator needed bleeding by undoing the bolt on the top and bleeding it like the radiator on your central heating system with the system cold. Once the bubbles stop and coolant starts to dribble tighten and then start up. The excess coolant in the expansion bottle will disappear in a blink! Considering that the first fill pack gives you twice as much gearbox and diff oil and brake/clutch fluid as you need not providing enough coolant is a bit mean. The advice from the factory was "we'll top it up when it comes in". Its now at Dartford for checks and IVA.