Radiator Differences

[Tim Leech]

Will a 1.9D radiator fit a 1.9 petrol BX chaps? The one on the TRS estate is rotten, I have a new one for a 1.9D, new ones are avaialble for the 1.9 petrol but are pricey (they are larger than a 1.6)

[ACCM Jelle]

In the spare parts catalogue the water hoses are at the same place at both radiators. But what about the volume of the radiator? If its the same,then I had no doubt to build in.

Greets Thomas

[Tim Leech]

They look the same size, and woukld a slightly bigger capacity radiator be an issue?

[mat_fenwick]

Not a problem if it's bigger - you would get potentially more cooling capacity which would be a bonus.

[rutter123]

Why not plug the bottom hose hole and fill the rad with water to see how much it holds, then do the same with yr old one, i guess if the difference is minimal then you will be ok.

[mat_fenwick]

Why would it be an issue even if the new one holds a lot more water?

[Tim Leech]

Cheers guys ill see if it fits and let you know. I wonder if estates have bigger rads as they all have the short nose bonnet and grille.

[ACCM Jelle]

I build a radiator from a TurboDiesel in my 1.6 petrol for better cooling when driving with caravan.

[Tim Leech]

Excellent I was just concernced about water flow and the pump being suitable for the job.

[Vanny]

Why would it be an issue even if the new one holds a lot more water?

I understand that the combustion cycle likes a fairly specific (tunable) temperature, the best efficiency will be at a given block temperature. Too much, or too little cooling could have a detrimental impact on efficiency. This can be influenced by an over or undersized radiator and different core type (fin pitch, density, core size etc).

That all said, i suspect in this instance the difference will be minimal and the influence on efficiency little (compared to other influences).

[Dollywobbler]

I would have thought the thermostat would still control the engine block temperature. I drive a minibus with an extra heater just plumbed into the existing cooling system. It does take a bloomin' age to warm up, as the extra pipework is all the engine side of the thermostat! A larger rad should just mean it'll take longer for the fan to kick in.

I have driven a BMW 5-Series six pot with a four-pot rad. While towing a loaded car trailer. On a hot day. Heater on full blast to try and keep it cool! Can't see that going the other way would cause much bother.

[Vanny]

I would have thought the thermostat would still control the engine block temperature.

The 'thermostat' is there to try and hold the engines minimum temperature. ie if the block is cold, or the radiator is cooling too much, it shuts down part of the circuit.

It's easy to forget in our moderate climates, but even in the 70's (when the 'XB' was first worked on) the BX would have been designed to run in both very cold (-30c) and very hot (+40c) ambient temperatures. In the UK we could do without the thermostat for much of the year, but probably not in Sweden etc

[mat_fenwick]

the BX would have been designed to run in both very cold (-30c) and very hot (+40c) ambient temperatures.

By which logic, if there is enough cooling capacity to keep the engine at optimum operating temperature at 40 deg C (whilst climbing a hill and towing a trailer) the rest of the time it would be overcooled unless the thermostat restricted flow. Which is exactly what happens when you remove a 'stat or it sticks open, even in UK temperatures. The gauge will cool right down when descending a hill, and often during high speed (not flat out) motorway driving. It's only when working hard or when stationary/slow speeds that the needle will approach the normal position on the gauge.

So with a larger radiator, the 'stat will restrict the flow more than it would with a standard radiator. I guess if you really looked for it, you may see a bigger dip in temperature when it first opens after a cold start - as the greater mass of cold water in the radiator hits the hot engine. But apart from that I can't see any effect you would notice.

[Kitch]

the BX would have been designed to run in both very cold (-30c) and very hot (+40c) ambient temperatures.

By which logic, if there is enough cooling capacity to keep the engine at optimum operating temperature at 40 deg C (whilst climbing a hill and towing a trailer) the rest of the time it would be overcooled unless the thermostat restricted flow. Which is exactly what happens when you remove a 'stat or it sticks open, even in UK temperatures. The gauge will cool right down when descending a hill, and often during high speed (not flat out) motorway driving. It's only when working hard or when stationary/slow speeds that the needle will approach the normal position on the gauge.

So with a larger radiator, the 'stat will restrict the flow more than it would with a standard radiator. I guess if you really looked for it, you may see a bigger dip in temperature when it first opens after a cold start - as the greater mass of cold water in the radiator hits the cold engine. But apart from that I can't see any effect you would notice.

Thermal shock....not good

[mat_fenwick]

True, but we're not talking about a massive increase in size - there's going to be some thermal shock regardless - this would be no worse than what a 1.9D would see with its standard radiator. Maybe if the new one was double the capacity it'd be an issue long term, but I don't think it would be significant in this case.

As an aside, if you guys are building a high performance car with a massive cooling system capacity, do you do stuff like drilling bypass holes in the thermostat? I guess that would help, especially on a fragile tuned lump.