Looking into oil/water heat exchangers - Which one have you got Chelspeed?

[V7 SLR]

Wotcha Chelspeed. I remember we talked about your oil/water heat exchanger, and I reckon that it is the best control over oil temperature I've seen. I have the large race ali radiator so I have lots and lots of heat-sinking capacity, and don't fancy an oil cooler as they don't have a thermostat. It is my belief that oil needs to get hot, and an oil cooler rather indescretely cools oil regardless of its temperature.

 

My question: which one of the heat exchangers listed in DT's was the one you bought, and how did you make your decision? I believe that the efficiency of a heat exchanger is proportional to the temperature difference between the two liquids and the size of the heat exchanger. I hope that's right. The water temperature is controlled with a thermostat (a lower 74 degree one to be fitted soon in line with current thinking) but I don't think I would want oil temperature that low would I?... not that it is possible, as there still needs to be a temp difference for the heat exchanger to work.

 

My objective is to more quickly raise the oil temperature on start-up, and to try to limit the increase in oil temperature during hot runs through Europe and on track. Anyone who thinks that you only get oil temperature increases on track need to talk to one of the Euro2001 tourers. smile.gif

 

So, I need to know what temperature range is best operating temperature for the oil in my engine, and what size of heat exchanger would be required to make this happen given a steady state water temperature of 74 degrees. Is it possible to calculate or do we simply go and buy the middle-sized one and see what happens?

 

Where do you take off the water supply for the heat exchanger, and where do you take off the oil supply? I have a perfect place for both, but am worried there might not be enough flow in these areas. Now I know you're not a K man, so maybe one of the other K'sters could help....

 

... I have no heater, but there is still a water pipe that loops round the engine bypassing where the heater would go. It's quite small in diameter, especially when compared to those feeding the radiator. Are they big enough for this type of appication? As for the oil, well with the dry sump I thought to split the bottom aeroquip hose linking the bottom of the dry sump tank to the oil pressure pump, passing the oil from here through the oil part of the heat exchanger. This seems a sensible place as the temperature of the oil coming out of the heat exchanger would get fed directly into the engine.

 

I have a few modifications planned this Winter, and aim to start collecting parts immediately hence the enquiry.

 

Thanks.

[Chelspeed]

Hi Nudger!!

 

Sorry for delay, been on hols...

 

Mines the middle sized one, 180mm element, listed as 245mm in Twats catalogue. I chose that one because Steve at SBD had one on his engine which was similar spec and it worked. Oh and if you're fitting it in the main radiator hose (see below) you need smaller than standard water connections to suit the Caterham hoses (32mm from memory). See http://www.thinkauto.co.uk/ for more details.

 

On the water side mine's plumbed into the radiator outlet, ie cold side of the radiator, in the big hose that feeds the water pump suction. I've no idea what temperature the water is here because the temp sender is on the inlet side of the radiator. I understand it's generally about 15 degC colder.

 

On the oil side it's between the scavenge pump and the inlet to the dry sump tank. The reasoning behind this is that it minimises the head loss in the suction side of the oil pressure pump.

 

I think in an ideal world I'd try the cooler in the radiator inlet pipe to maximise the oil warming effect on start-up (but you'd still not get any effect until the t'stat opened of course). This would mean warmer water so less oil cooling. What stops this is packaging. There are no oil pipes anywhere near the top hose but the bottom hose is right next to the oil pump so it's easy. So I tried that and it works so why change?

 

How well does it work? Well I saw oil temps of around 120 degC before I fitted a cooler. With a 70 degC thermostat I see water temps of between 70 and 75 degC on the road and up to about 85 degC when sprinting. Oil temps are generally between 5 and 10 degC hotter, so 75 to 80 degC on the road and 80 to 90 degC when sprinting. Not done any track days or races so can't comment on that.

 

Are you coming to Curborough this weekend at all? If so then you can crawl around the car and have a look then.

[murph7355]

I've one of these on my DVA'd K-series.

 

On very hot Le Sept days with some serious thrashing the oil managed to get to 100degC but no higher. Typically it's about the same as the water temp (75 to 80 - which I believe is ideal. In traffic on the Peripherique in v.hot ambients it did get to 85 or so).

 

I'm pretty certain it's the 180mm size also and (forgive the lack of tech. detail) is longitudinally installed to the front left of the engine if looking from the rear (you can just see it on one of the photos on page 8 here.

 

I have the big ali race rad too but, perhaps importantly, am not running a tstat at all. I guess the danger of this is simply that the engine won't heat up as quick (i.e. water temp) but in practice it doesn't seem to be a hassle at all (oil and engine temps get up to sensible levels very quickly, even last winter). And it's one less bit to break/replace (saves you 3 quid or so too)!

 

I don't have a dry sump (just yet) but do have an Apollo. I'll hopefully be picking the car up this week some time so might be able to get some photos done for other details.

 

Another couple of advantages for these are that they can be installed pretty much anywhere, pipe runs allowing as they do not need to be in the air flow, and they can be cleaned if your engine lets go (god forbid! I guess you'd have a bit more to worry about though then - "never mind dear, at least my 100 quid oil cooler won't go to waste"...).

[V7 SLR]

Chelspeed, I can't make Curborough this weekend unfortunately. My Se7ening days may be over this year due to the many over-Winter jobs that I've built up recently. The car's just had a new ECU and I want to make sure it is properly RR'd before I use it again. That's booked in for 22nd Sept. And then there's those illegal tyres.... Dammit.

 

I'm not so worried about massive cooling. I'm more concerned that the oil temperature becomes regulated. I will be running a 74 degree stat after the Winter and with the large race radiator I believe there's enough thermostatically controlled stability in the water system to regulate the oil system too.

 

I've looked at the optimum place to site this thing and I reckon the oil part needs to go between the bottom of the dry sump tank and the entry into the pressure pump (for want of a better word). This way, all oil going back into the engine will be at the optimised temperature.

 

As for the water side, I agree that I should use one of the radiator in/out pipes simply because of there great capacity, but wish to utilise the part of the water system that's the engine-side of the thermostat, and so fully take advantage of start-up warming. The obvious pipework to use to that end is that which circles the engine, normally used for the heater when installed. The downside is that it is a very small diameter pipe which means less flow than through the radiator. I simply don't know whether that'd be enough.

 

I'm not keen on running without a thermostat as Andy is. I'm less concerned with overall cooling than I am with regulated temperature. I firmly believe this is the way to optimise.

 

I have decided that, price aside, the sensible method for determining which heat exchanger I choose is to go for the biggest my engine bay can accommodate. All things being equal, if you assume that 74 degrees is a good overall temperature for the engine (this assumption is based on the "Minister" article in Low Flying), and you need to get the oil as close to that as possible, then you need to consider the factors I mentioned earlier, namely the efficiency of a heat exchanger being related to the size of the interface between the two fluids and the volume of fluids being passed through it. The other factor is already fixed, that being the difference in temperatures between the 2 fluids - the temperature of the water system is set at 74 degrees by the thermostat and the oil by whatever it runs at (God-only knows what that is though, as it depends on where you measure it).

 

The next project is to see if I can measure the temperature of the oil at various points in the circuit. I already have a sender in the bottom of the dry sump tank (not optimally positioned) but I would also like to see if I could measure it on it's way out of the engine (scavenge pump outlet), and between the heat exchanger and the pressure pump (when installed). I'm not sure I'd want permanently positioned senders placed in those locations, but it'd be interesting to see if there are any differences in the temperature of the oil in those locations, and to what extent.

 

Does anyone have any insight as to the extent of the water-flow through the heating system pipework? Is it under pressure from the water pump?

[Peter Carmichael]

V7,

 

Your oil side siting for the exchanger is a bad choice for the reason that Chelspeed has said. The only thing *pushing oil into the pressure pump* is atmospheric pressure. You will be putting an obstacle in this pathway and there will be an appreciable pressure drop and earlier onset of cavitation in the oil pump at high revs.

 

You should definitely site the exchanger on the pressure side of a pump. The scavenge pump is the obvious choice as you have external piping from it already.

 

The plan for the water side is OK. You shouldn't be thinking of it as the heater hose necessarily because it is a part of the coolant circuit by its own right. I think the coolant bypass piping will work effectively. If you start dumping a lot of heat into that pipe, the thermostat will attempt to compensate. Essentially, the oil dumped heat will make a further circuit through the head before ending up in the radiator.

 

I am planning something similar.

 

Peter

[oilyhands]

FWIW my oil/water HE is sited in a sandwich plate between block and oil filter, the water supply is plumbed directly to the head/bypass circuit so that it sees the benefit of warm/hot water well before the thermostat opens, this gives the best possible warm up times and keeps the oil at a reasonable temperature at all times. It is always best to have the heat exchanger on the pressured side of the oil supply since it creates a fair bit of drag on the oil, its also much more convenient to plumb it this way on most engines.

 

Oily

[V7 SLR]

Hmm, siting the HE on the output from the scavenge pump actually makes locating it in the engine bay very much easier. This means I can now remove the conning tower connection from the scavenge pump and plug that into the HE, and take the output from the HE into the conning tower. It also means the "heater" water circuit is very close by too. Very convenient.

 

Thanks.

 

One other comment: By locating the HE in the "new" position, this makes my attempts to be scientific about the exact temperature of the oil prior to it entering the engine less controllable I think. I can now control the temperature of the oil as it gets dumped into the dry sump tank, but on start-up this tank is a large pice of cold metal and will cool my just-warmed oil down again. Certainly, the science of regulating the oil temperature once the whole schebang is warm still holds true, but my improved warm-up ability is a little reduced now I reckon. That said, it's still better than the present situation. Should I be happy about this anyway?

[Chelspeed]

Definetly think oil wise it should go on the outlet of the scavenge pump so we're all agreed there.

 

Putting the water side in the heater pipe sounds good. Someone on the Se7ens list described doing this and fitting a blank in the main bore of the water side to force water thro the outer ring of water tubes. I'd read about this in the instruction sheet or on the Think page but couldn't understand what they were getting at. Now makes perfect sense and seems like an all round ideal location - Provided there's enough flow to loose the heat you want to. If not then you can easily shift it to the rad hose later

 

On size I'd stick with the middle one. If it can cope with an inefficient Vauxhall engine then it'll be OK with yours I'm sure.

 

So you're not competing at Curboro, but you'll still be coming for a chin wag though?? After all it's only just up the road for you....