Update on Low Temperature Thermostat Tests

Update on Low Temperature Thermostat Tests

Author
Discussion

hartech

Original Poster:

1,929 posts

231 months

Tuesday 24th December 2013
quotequote all
It is several years since we last conducted the engine running temperature tests that resulted in the provision of the "low temperature thermostat" and we thought we should revisit the tests to be sure our advice provided since is still valid and to check several questions that readers have asked since about how to minimise the risk of bore scoring. Our original tests were carried out at this time of year and we know that in the Summer the temperatures are a little higher and the difference between std and our low temperature thermostat is slightly reduced by about 2 degrees.

In a standard 3.8 997 (with no Hartech machining mods to the coolant flow in the blocks i.e. as your standard car would be) but with 6 temperature sensors fitted to the engine and simply with first a standard and then a Hartech Low Temperature Thermostat we have just conducted back to back tests on the same day, routes and speeds etc and recorded temperatures driving, stationary, after ticking over for 2 and 5 minutes, switched off and on again after 5 and 30 minutes and at town and fast road speeds with the following results.

(1) Despite the temperatures recorded varying from 79 to 104 the dash board temperature gauge read 80 for every reading - confirming that the instrument in our test car has a buffer zone of about 25 degrees during which it does not change nor reflect what is going on in the engine or the coolant. This may lead to some who have fitted such a thermostat to question if it was doing its job! which it probably will be (and certainly will be if it is one of ours) .

(2) With the standard thermostat - on average the thrust side of bank 2 ran 5 degrees hotter than the thrust side of bank 1 @ 93 and 98 respectively. In contrast- with the Hartech thermostat - the difference was only 1.6 degrees @ 83.8 and 85.4 and this shows that the thrust side of bank 2 is now running cooler than the original thrust side of bank 1 (where we do not experience bore scoring failures).

(3) The oil temperature was on average 9.9 degrees cooler with the Hartech Thermostat (100 and 90.1).

(4) Whether driving slowly in traffic or fast on an open road the temperature differences between bank 1 and bank 2 were not significantly high (because at slow speeds there is little temperature generated anyway and at high speeds both the engine revs and air speed through the radiator are higher and overall cooling very efficient).

(5) The major difference was obvious when the car was either stopped but running on tickover for a few minutes or stopped for a few minutes with the engine switched off and started again. In both cases bank 2 thrust side increased temperatures much higher than bank 1 (because the contra-flow works on bank 1 and maintains a more even temperature gradient inside the engine whereas bank 2 exists with a higher temperature range that soaks out when the coolant flow reduces or is stopped) . On tickover or with the engine stopped - the oil around the piston in bank 1 and bank 2 would naturally gravitate to the bottom this would leave the piston in bank 2 thrust side (the top) with less oil on the thrust face for a restart and much hotter and thinner to resist the high torque loads possible driving off again - while bank 1 piston would be cooler and carry more oil on its thrust face (the bottom) for the re-start. This confirms our advice to drive off modestly after a period stopped at say lights or for a brief engine "off and on" stop before opening the engine up again. It also confirms that high speed driving at higher revs should not be a problem (as it has not been also in our race car engines).

(6) With both thermostats bank 2 cylinder head ran slightly cooler than bank 1 (96.7 to 98.1 std and 87.2 to 89.2 Hartech).

(7) The engine under test is fitted with pistons with yet another pair of different coatings and when it is stripped for the first time to check wear rates - we will modify the coolant flow to reproduce our usual rebuild changes and test out the results of those again too.

(8) In general the fact that the thermostat is fitted on engine entry did not de-stabilise the temperatures but of course resulted in much higher internal running temperatures and thinner oil film strength than was the case when thermostats were fitted to the outlet. Assuming the same thermostat was fitted either before or after the cylinder block - the difference in internal cylinder temperatures would be about 8 or 10 degrees. The fact that the std thermostat is rated higher than those tradditionally used in more conventional engine coolant flow layouts would also mean that the internal engine temperatures std are probably in the region of 10 to 15 degrees hotter than they used to be (and all to assist the emission reductions required to export cars to major outlets).

Similarly with the more traditional layout the higher internal coolant temperatures were maintained the same as the engine usage was increased through faster more aggressive driving whereas with the thermostat on the inlet - as the engine is worked harder - so too does the internal temperature range increase.

I am not sure if it is an advantage to use a thicker oil if a lower temperature thermostat has been fitted (as the running temperature reductions will inevitably result in the same oil holding a higher viscosity) but personally - once any new parts have been run in - I still think an upgrade (as Wizard proclaims( is a benefit likely to extend the engines life).
It must be remembered that fitting a low temperature thermostat will not repair any existing wear rates that might have worn down the piston coasting somewhat already and therefore although running the engine at a cooler temperature may have avoided bore scoring all together if adopted when the car was new - with scored bores on bank 2 having occurred @ 9000 miles (but more usually about 30 to 60K) and as yet no evidence of scoring on bank 1 even up to 100K - it does seem that the temperature difference between the banks is what promotes early bank 2 failures and therefore although reducing those temperatures in bank 2 should extend piston life significantly, it is impossible to establish how worn they may already be at the time of fitting the low temperature thermostat and therefore being unable to predict how long the benefit will last for afterwards.

Although the low temperature thermostat is a low cost way of improving reliability - we are still working on hopefully even better solutions both for retro-fitting new designed parts to existing cars and during rebuilds. While fitting 6 Nikasil cylinders removes the problem all together - it is still expensive and so despite trying several different coatings unsuccessfully to date - we are still working on finding a reliable piston coating that may enable us to overbore scored cylinders that combined with changing the coolant and cylinder block temperatures - may eventually reduce rebuild costs with much improved long term reliability to "Nikasil" levels.

Finally I am not sure why there seems to be some form of competition to demonstrate where readers obtained their own lower temperature thermostats from and at what price - ours is just £35 + Vat and these test results only apply to our thermostat and do not necessarily apply to any others.

Have a great New Year - and "KEEP COOL"


Baz

Trev450

6,542 posts

186 months

Tuesday 24th December 2013
quotequote all
A very interesting read once again, Baz, and reinforces my decision to have fitted one of your low temperature thermostats to my gen 1 987.

Shurv

1,012 posts

174 months

Tuesday 24th December 2013
quotequote all
Great feedback, thanks for that Baz, really interesting. Mine is a genuine Hartech one..........smile

Bebs

2,927 posts

295 months

Tuesday 24th December 2013
quotequote all
Thank you Baz. Grant is currently rebuilding my engine and I note the low temp th. Is part of the new parts. Looking forward to getting it back!

6C4GTS

5,185 posts

192 months

Wednesday 25th December 2013
quotequote all
hartech said:
Finally I am not sure why there seems to be some form of competition to demonstrate where readers obtained their own lower temperature thermostats from and at what price - ours is just £35 + Vat and these test results only apply to our thermostat and do not necessarily apply to any others.
Baz - I was looking at fitting a low temp thermostat to my 3.6 996 in the new year with my next service - your website says £42 + vat...should I be asking for a PH discount to get the thermostat for £35 + vat.

Cheers

hartech

Original Poster:

1,929 posts

231 months

Thursday 26th December 2013
quotequote all
Scores are usually too deep to hone out and there will usually be damage to the crystal structure of the remaining silicon bits making them more likely to fail as well - so in most cases a new liner is necessary.

Sometimes light polish marks can be re-honed to increase oil retention and run in new pistons and rings - but each case has to be analysed and then the best recommendations made to the customer - usually with some alternatives for them to consider.

The price will be £35 plus packaging and Vat but I will speak with the guys back at work when we return to clear up any anomalies.

Baz


edc

9,431 posts

265 months

Tuesday 31st December 2013
quotequote all
I know you guys do a lot of testing but without wanting to start an argument why would one buy your low temp stat versus another one? Does your's work differently? It's not obvious if it does. The reason for asking is that I have recently bought a low temp stat. Of course I wanted a good price but for the non-tech enthusiast like me my approach was to look for some recommendations, scour the web, find the right product then choose a reliable supplier/retailer. In this case it happened to be ebay, my search just didn't take me down a path your way for whatever reason.

hartech

Original Poster:

1,929 posts

231 months

Tuesday 31st December 2013
quotequote all
Well we have not tested any other thermostats but when we first tested the engines and worked out what we wanted we had them made to our specification and as far as I know they are exclusive to us.

The speed at which they open and the range from just open to fully open can vary and the coolant pump design has to be taken into account. Centrifugal pumps can displace a lot of coolant through a relatively small gap or only slightly open thermostat - so to obtain the response we wanted (which anyone who has one will have noticed is extremely stable) has more to do with the design than just buying one with a particular temperature setting to open. We had to pay a lot to get the design we wanted in quantity to keep the price reasonable as well.

However I do think most available will probably do the job just as well.

The only reason I mentioned it is because it puzzled me why so many contributors feel the need to tell others where they got one from when they usually pay more and for sure no similar testing has been carried out by those suppliers - that's all. We do not make enough out of selling them to make any kind of competition for sales to be worth bothering with but we do continue to invest a considerable amount of time and money into developing various different solutions that are a great benefit to consumers and I find it odd that some do not consider returning some appreciation by way of product supplier loyalty and prefer to spend more to buy one elsewhere and then cannot seem to wait to tell everyone else about it. It is an easy thing to copy once development costs have been spent but there will have to be a limit to our own future development expenditure if we have to factor in reducing returns as a result.


Baz

edc

9,431 posts

265 months

Tuesday 31st December 2013
quotequote all
Thanks. To be fair at the same or similar price point I would have happily and probably preferably bought one of your own ones had I come across it. I get that parts and product sales is not what your business is about but the text you write makes a compelling sales ad which is nowhere to be seen on your website.

JarmoL

107 posts

164 months

Tuesday 31st December 2013
quotequote all
Would this low temp thermostat fit/benefit GT3's as well?

steve singh

3,995 posts

187 months

Tuesday 31st December 2013
quotequote all
Thanks Baz.

Which company first came up with ltt?

Trev450

6,542 posts

186 months

Wednesday 1st January 2014
quotequote all
JarmoL said:
Would this low temp thermostat fit/benefit GT3's as well?
Given that it is specced for the 'issues' surrounding the 986/7 and 996/7 non GT engines, then I doubt it.

Edited by Trev450 on Wednesday 1st January 09:42

hartech

Original Poster:

1,929 posts

231 months

Wednesday 1st January 2014
quotequote all
It is a strange subject - engine cooling seems one of the simplest technical issues to master yet is actually extremely complicated and can be confusing.

A lot depends upon the position of the thermostat, the capacity of the radiators and the volume delivery potential of the coolant pump.

As long as the car as a whole has the capacity to cool under any normal circumstances - then the following applies.

If the thermostat is on the engine outlet then you are controlling the maximum temperature that the engine can run at but variations in driving styles and conditions, air temperatures and wind speed etc all influence the engine entry temperature. If you add more cooling capacity the entry temperature will go down because the thermostat will slow the flow through the engine and increase the temperature gradient as the coolant passes through the engine. It is not a good thing therefore to have too much cooling capacity as this simply increases temperature gradients inside the engine.

If the thermostat is on the entry to the engine - you are controlling the entry temperature and so differences as described above will raise or lower the temperature gradient in the engine and alter the outlet temperature. In this case too much cooling capacity will slow the coolant flow and actually increase the engine outlet temperature.

So getting the right amount of air flow through the radiators, the right radiator capacity (core numbers, depths and spaces), a pump that can vary flow rates as the thermostat opens etc are all part of quite a complex design.

The issue with M96 and M97 engines is that the coolant flow is different in bank 1 and bank 2 and this results in the temperature in bank 2 near where the pistons and cylinders score being hotter than in bank 1. Then there is the fact that bank 2 is where the problem is and not bank 1.

It is difficult to conceive a way to alter the internal coolant flow but the LTT does help lower the temperature in the critical area of bank 2 but in fitting it bank 1 is running even cooler than before when it didn't give a problem.

Of course if the basic cooling capacity of the system is the problem it may need extra radiator area, air flow, coolant speed etc - but most manufacturers can get all this right.

It is unfortunate that our tests prove that during a pause after a fast run - when idling - the bank 2 outlet temperature raises significantly (because both coolant flow and air flow are reduced while heat is still soaking into the engine). This is not directly shown up by the dashboard temperature gauge because not only is it damped to give false readings but it also measures the mix of coolant from both sides of the engine and the head (with about 85%) and the cylinder block (with about 155) of the flow mixed back together sgain. It shows a general increase but not the individual affect on bank 2 cylinder thrust face. It is only tests like we have set up with individual sensors fitted to crucial areas that can identify these issues and work out what the problems are.

A coolant pump that is not controlled by the engine speed could help reduce this if sensors were placed in the right place and controlling the right pump speed so it could speed up coolant flow when the engine is idling but the engine soak is high - to avoid driving off again with hot cylinders with low oil viscosity between the pistons and cylinder bore - especially when this is aggravated by the fact that bank 2 oil film will naturally run away from the thrust face downwards under gravity while bank one does the opposite and fills the thrust face area.

The problem for small businesses trying to help owners when the manufacturers have not avoided a problem or solved it - is high because they neither have the financial resources to do as much as they would want to - nor the eventual control over spares supply that would result - to ensure a return on their development costs.

I don't imagine it is important who did what first - just that some people have properly investigated and tested things out while others have just sold something similar because there is a demand they can make a return from.

We continue to test different issues as much as we can and you will find that we have new improved solutions under test that could make engines last much longer even than the LTT. We are also going to fit extensive test capture systems to our 996 race car for 2014 - to further learn and test out what is going on - doing as much as we can and we can afford - but we cannot continue to do this if we never get a financial return for all the investment and that needs some customer loyalty to those businesses that do try and help - to sustain their efforts and to improve things for owners.

That is my message for 2014 - whoever they are and wherever they are based - it would improve things for everyone if owners could show some appreciation of those businesses that are investing in solutions despite their relatively small size compared to the manufacturers who seem unwilling or unable to support the ownrs of products they failed to make as reliable as they should have been.

Baz

Trev450

6,542 posts

186 months

Wednesday 1st January 2014
quotequote all
Once again Baz a very informative post.

If the worst should happen to my M97 engine, I would have no hesitation in bringing it to you to be rectified.

steve singh

3,995 posts

187 months

Wednesday 1st January 2014
quotequote all
Trev450 said:
Once again Baz a very informative post.

If the worst should happen to my M97 engine, I would have no hesitation in bringing it to you to be rectified.
+1

jcelee

1,074 posts

258 months

Wednesday 1st January 2014
quotequote all
Baz, thanks again for the spoils of your testing.

I know its rare but have you ever seen significant bore scoring on a 987 2.7 engine?

Many thanks.

hartech

Original Poster:

1,929 posts

231 months

Thursday 2nd January 2014
quotequote all
No The smaller capacity engines use the same basic cooling system and flow yet generate less heat in the piston area - especially at low revs where the significant difference is less torque. Most piston scuffing is thought to occur at low revs and high torque which the bigger engines create more of. Drivers therefore tend to rev the smaller engine'd cars more before changing gear or opening the throttle more to get better acceleration and this seems the best way you should drive the bigger engine'd cars as well.

This may be why it seems more 3.8 tiptronics suffer than manuals as we have found drivers tend to run a manual at higher revs in each gear before changing gear whereas the torque converter allows the revs to rise with throttle opening and tend to be driven at relatively high throttle openings from slow speeds but not enough to kick down.

Effectively the smaller engine creates less loads and heat to dissipate and therefore - cool better, maintains better oil film strength between the piston and the bore and lasts longer.

I guess they may be a problem one day in years to come as basic wear on piston coatings eventually takes it toll but the smaller the capacity the longer it should last.

Baz

petop

2,291 posts

180 months

Thursday 2nd January 2014
quotequote all
Good post Baz, and hence why in my 3.6 Tip i drive in manual and pull away in 1st. Takes some getting used to but the usual negative aspects of a Tip are gone, still prefer a PDK though.

was8v

2,003 posts

209 months

Tuesday 7th January 2014
quotequote all
hartech said:
Finally I am not sure why there seems to be some form of competition to demonstrate where readers obtained their own lower temperature thermostats from and at what price - ours is just £35 + Vat and these test results only apply to our thermostat and do not necessarily apply to any others.
Baz great post. However some advice:

Your forum articles are renowned in the community for being well informed, researched and authoritative. Your work has an excellent reputation.

Your website does not really reflect this. Your articles and research findings should be written into articles published on your own website!

For example your website states your thermostat is £42+vat not the £35+vat you say above. If you had a page with your article above and an up to date price and online ordering on the website, you would get more sales.


hartech

Original Poster:

1,929 posts

231 months

Tuesday 7th January 2014
quotequote all
Thanks Was 8V we are well behind on bringing our web site up to date but it is in hand - a whole revamp with a modern subject selection system - but it is a big job and meanwhile I try to respond to owners greatest needs for advice and fears of which the bore scoring seems particularly prominent.

The racing with 4 cars last season really took a toll on our time but the results were well worth the effort - now we need to get back to other stuff.

Recently we have built a customer area at the factory with Internet Access imminent and a race car simulator (to keep customers occupied when waiting), there are a lot of technical developments going on still and more technical stuff to get the race cars even more competitive and hopefully reliable - so we are not sitting around doing nothing and meanwhile engine rebuilds and repairs grow on an ever rising scale.

No chance to get bored in 2014 either.

I hope we can keep up the reputation and even improve it if possible - but many thanks for your appreciative comments - it makes it feel worthwhile.

Regards,


Baz