Low Temp Thermostat

I just wanted to have a little debate about the low temp thermostat and what it will actually do for your engine. I've read a load of stuff where people have fitted them expecting their car to run cooler and help prevent bore scoring but as far as I can deduce it'll do nothing at all for keeping the temp down on your engine especially if you're driving in a warm climate. So the thermostat is there to ensure the engine warms up quickly or another way to look at it is to prevent it running cool for too long...agreed? Once you start the engine and begin your journey and your're flying down the road a low temp thermostat will open probably a few seconds before a normal temp thermostat , that is the only difference I can see. If you then hit a traffic jam and the engine is sat there idling , it'll very soon hit the temp at which the fans kick in , they to me are the key to preventing your engine overheating , they need to kick in bang on time and be working as they should , and they do if everything is good...the engine bay fan is also included here. The same thing would happen if you completely removed the thermostat , only it'd take a long time to get up to operating temperature which isn't good either. So I really don't know why you'd bother with one., I mean they won't do any harm but I don't think they have any advantage to the stock one. Make sure your radiators are clean and your fans kick in before temp rises and apart from a third radiator (like Turbo's) there's not much else you can do. Hopefully someone can prove me wrong. Actually there is one scenario that would allow your engine to run cooler, lets say its cold and you're driving on the motorway in a high gear at low revs , then I think the engine wouldn't be able to create enough heat to make the coolant rise to normal temp (vertical on the dial).

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Surely it is there to make sure it doesn't just keep getting hotter and hotter? It will open and let cold water to circulate to make sure it doesn't get too hot, if it does the oil will also get too hot and the oil isn't just a lubricant it is also a coolant. The Hartech LTT tries to keep the oil temps around 88ºc from around 92ºc with the standard thermostat. That is oil temp being measured where it is being mixed, the oil temps in the cylinders can be considerably higher especially when the car is being worked really hard, which can thin the viscosity too much between the piston and the cylinder. It only gets a bit too hot, but that is enough to cause scoring and tends to be on bank 2, bank 1 tends to be OK because that is where the cooler coolant flows in. Not saying if it is a winner or not, but that is the thinking behind it.

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Precisely my understanding…and I don’t think sitting in traffic is problem for bore scoring, or is it?

The thermostat will be fully open quite quickly , once it's open it can do absolutely nothing to prevent the engine getting hotter and hotter, that's the job of the electric fans and the radiators ...nothing else.

I suppose in a cold climate like the UK (I mean it's been 12C all day today here in Scotland) a low temp thermostat would actually work as there will be an "excess" of cooling available for the engine in nearly all driving conditions and the LT thermostat will be opening and closing to maintain the lower temp. But in a warm climate (25-40C) I would have thought the thermostat will be open fully at all times and the fans will be close to firing up as soon as the air flow stops , like at a set of traffic lights for instance.

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But the system is designed to keep the coolant temp at the optimum temp range, which on these is actually between 101ºf and 194ºf. The thermostat is not just an on/off switch, it is constantly moving which changes the flow. The LTT stat just means it is changing slightly quicker and at a lower temperature point. The regular 'stat starts to open at 88ºc and is fully open at 99ºc, the fans kick into high speed at 104ºc which will then start to bring the temps down or keep them from raising if sat in traffic in the heat. But if you watch the coolant temps using Durametric the temp stays around 92ºc which tells me that the 'stat is not fully open during normal driving and is still being regulated. I don't know if this is the case, just what I have observed. The LTT brings this operating temperature down a few degrees. I agree, keeping the rads clean and making sure your fans are working properly is the most important.

Agreed. It'd be interesting to get feedback from someone that's fitted one but like you say it will be constantly adjusting the flow of the coolant to the radiators to maintain the temp. I thought the thermostat would be open all the time during normal driving but this is not the case then and a LTT could be a good option if you get the opportunity.

I had one on my last 996 from the day I bought it. I now certainly notice it, because my current 996 doesn’t have one and it definitely runs hotter.

I fitted a LTT onto mine from Heritage parts centre together with a new housing and gasket. According to Hartech it's not simply the decrease in oil temp that is the benefit, but getting the coolant flowing earlier in a potential scoring situation. The idea is to get ahead of the localised oil overheating by increasing radiator flow a few seconds earlier than normal. Add some Porsche A40 spec 5w50 and you have even more hot protection. This is what I use personally but Hartech use a non A40 spec oil.

Well yeah, the coolant keeps the cylinder walls from getting too hot and thus expanding, but it also keeps the oil in the engine cooler too. The flat six design doesn't like oil getting to the point where the viscosity is no longer doing its job properly, especially if the cylinder has also got too hot. I think the design is just asking for trouble without strong enough liners. Laying on its side, long circuit for coolant to get to the end of bank 2, it is a surprise they make it off the dealership forecourt!

I have always found this conversation facinating, my understanding is LTT just turns on the fans earlier, what use is this? (unless the cooling system is rubbish). I believe mine is a bit rubbish (latish gen 1) and the temp goes up further than I'd really like (until second stage fans come on) but this means to me that I need a third rad (fitted as standard on some) or my preference a set of CSF (costly). I suppose it depends on what you are doing, in a road car I'm more interested in getting the oil temp up to operating level than turning on the fans on earlier, but even on a race car it would be managing temps at full operating temperature as opposed to kicking in a fan early,

The fans kick in straight away, they come on with the climate, if you leave that off they will kick in at 97ºc, stage one and then 105ºc for stage two. The thermostat just lets the cooler coolant flow around the engine, it opens and closes over a temperature range, which keeps the temps under control. I never run mine with the climate off, It sits on the 0 of the 80, but this is weighted, actually sits around 89-96ºc in normal operating temps with diagnostics plugged in, around 92ºc 75% if the time. I guess that is why it is weighted, if it wasn't everyone would be panicking constantly.

Yes my (mis)point "my understanding is LTT just turns on the fans earlier" was incorrect so thanks for the correction. It does, as you say, initiate coolant flow at a lower temperature. Howver, even if you initiated coolant flow at start up the engine will still reach "whatever temperature it will reach" whether just driving or racing and the rads (plus fans) will still dictate heat control under stress so starting the flow earlier doesn't make sense to me and would reduce getting oil to temperature which to me is more important. Why would you want to initiate coolant flow early unless damage was being done before the fans could control things?

The engine doesn't just reach the temp it is going to reach though and then the stat is open, the thermostat opens and closes to allow the coolant to flow through the engine and keep the desired temperature. There is a target temperature set by Porsche, but some companies like Hartech think is too high for the cylinder materials used. Of course, sat in traffic the temps can raise even more, but then you are not revving the nuts off it while this is happening, and as soon as you start moving, along with the high speed fans the temp drops pretty quickly. The LTT is more to keep the temp around 88/89ºc rather than 94/95ºc the standard one achieves when pressing on. I don't have one fitted, I bought one, but I couldn't get my head round what it achieved and then by the time I did I realised my car never gets that hot anyway, and it is a 3.4 so don't really need to worry. The thing to remember is the stat is constantly opening and closing between 88-99c to control the temp. The LTT keeps this a smidge lower. If you put your actual temps up on the climate you can see them changing.

I check my oil is up to temp by dipping the clutch and seeing when it hits 1bar. This often happens earlier than the coolant temp hitting the middle of the 0 in the 80, unless it is really cold out, then it can take a bit longer.