V8R engine temperature control and solutions.

[J44EAG]

I`ll often use these Forum sites to formulate copy content for some of my future magazine articles. What you frequently see from me on this site, will often appear in the magazine at a later date, albeit in a much modified and edited format.

Here I`m on me soap box again about engine temperature control and how heat can be controlled in a supercharged application.

Elevated temperatures raise their heads with modified supercharged models. The more grunt an engine makes, the hotter the under-bonnet temperatures become. More heat spells trouble and unreliability. It gets worse the more upgrading you do to a vehicle. The heat radiates from the engine, the super-charger pressure manifold, the inter-cooler bricks and the exhaust manifolds. The more you up-rate the engine, the hotter it becomes. Something has to be done to help the rubber coolant pipes from disintegration whilst at the same time lowering charge air and engine bay temperatures generally. A hot engine can become inefficient if it runs at the hot end of the scale. Detonation within the cylinders becomes more likely and something just has to be done about it.

Raising ones arms to Heaven and shouting out, "This engine ain`t half hot, Mum!" does little to help. Desperate times need desperate measures. See my signature panel at the foot of this thread to see what modifications have been done to my car. Some raise the temperatures whilst other lower them. Let us see which ones make things hot and which one make things colder.

Heat increasing modifications.
Smaller supercharger pulleys - moderate impact.
ECU reflash - moderate impact.
OE small sized, low flow OE Hella inter-cooler pump - significant impact.
Sluggish high mileage OE thermostat with high 190 F (87C) initial opening temperature. Fully opens at 203F (95C). Very significant impact.
Inefficient inter-cooler radiator - during hot ambient temperatures. Low impact in cold conditions, more relevant in hot weather.

Heat reducing modifications.
Larger high flow Bosch/AVT inter-cooler pump -significant.
Ported supercharger and throttle body elbow - moderate.
Fast cats and X-pipe - significant-evacuates exhaust gas and heat faster. Reduction of back pressure reduces heat.
Methanol/water injection system - very significant - charge air chilling by Latent Heat of Evaporation theory. W/M mix injected into air intake, vaporizes when it hits the hot charger lobes and takes the heat out of the charge air and pressure manifold. Also lowers general engine temperatures.

Lower temperature engine coolant thermostat. As yet unfitted/unordered and to be trailed soon.
Mishimoto MMTS-54-00L Opens at 71C. Opens 16c earlier than OE stat. Significant.

I have noted that my car generally runs at around 91C with readings taken on my iCarsoft 930i diagnostic gear.

Internet searching suggests that an ideal engine temperature operates at its most efficient and at an optimum figure of between 68C and 84C degrees. It has further been investigated by practical rolling road figures that the Jaguar V8R range operate at their best at 82C. My car operates as said at around 91C. It is in my opinion therefore worth obtaining a Mishimoto thermostat as an experimental piece in the quest to further lower general engine temperatures to less blistering levels. Here is the link to this lower temperature thermostat.
https://www.google.co.uk/url?sa=t&rct=j ... FTh2LmNp_g

Eurotoys in the USA also market a similar stat. The price is reasonable at about £30 for this probably low demand part. The trouble starts when postage of around £70 is added...£70 just to shift a thermostat over the Atlantic!!!!
https://www.google.co.uk/url?sa=t&rct=j ... BmJUPeksPw
This piece of internet text make interesting reading.

V8 Thermostats.

According to Jaguar 2007 XK/XKR specifications the coolant thermostat begins to open at 190F (87C) and becomes fully open at 203F (95C). The 2010 and later models, with direct injection, may have a different thermostat, which I am unable to confirm.

I don't feel that an operating temperature of 203F is optimum for power and economy.
A lower temp around 185F (85C) is better at reducing detonation, which results in better power/economy. This applies to not only to NA motors but also to supercharged motors.

My reference source is A. Graham Bell, a Brit who now lives in Australia. Bell is a consummate tuner and has written several books, all of which are very readable. In his latest "Four Stroke Performance Tuning" at page 575 he writes:

"A high-temperature thermostat, which maintains the water temperature at 88-90C is usually fitted to production cars, but that is not the temperature for best power. The 88C thermostat is fine if you want good heater efficiency in winter, and the higher temperature partly compensates for the stock manifold and carburetor being unable to vaporize the fuel properly, but apart from that there is no reason for its use.

Some feel that high engine coolant temperature in the range of 90-100C is good for power. The theory is that anything lower just takes away heat energy, which we should be using to push the pistons down and produce more hp. To an extent this is true at low engine speeds and small throttle opening, but generally in a full-throttle, high-rpm dyno test an engine will make more power at coolant temperatures in the 70-80C range. Only dyno testing will confirm what is ideal for a particular engine, but in my experience I rarely see an engine that makes more power running higher than 84C or less than 68C. I have seen engines gain 2-3% more hp when the temperature was dropped from 90C to 70C; conversely I have seen gains when the temperature was pushed up from 65C to 80C."

My experiment was to find an aftermarket 180F (82C) thermostat that fits the Jaguar motor. In 2007 Jaguar went to a smaller diameter thermostat that is held in place in the black plastic thermostat housing by means of a small bridge-type bracket the is fitted into slots in the housing. Jaguar sells the housing complete with thermostat for well over $100. Far cheaper is the thermostat itself under part number "1 x AJ811788". This part comes disassembled; and is made in Germany.

I took my OEM thermostat to my local NAPA store to see if they could duplicate it in a lower temperature. NAPA has a #166 thermostat rated at 180F/82C. It sells for just $11.99. To install this NAPA thermostat requires using the locking bridge bracket from the OEM thermostat. Then the NAPA spring retention mechanism is redundant and can be cut out/discarded.

I won't get into the procedure to R&R a thermostat other than to say it is fairly easy on the NA motor.

The result is that my motor now runs in cruise at 184F/84C. It seems to get a bit better gas mileage on my 40 mile test run (flat freeway at 70mph). In stop and go driving temperature rises to over 200F(93C), but higher temperatures are limited/protected by the electric fan whose settings remain the same. I have not experience any real cold outside temperatures with this new thermostat. But, this is not my first experiment with cooler thermostats. With a 180F thermostat in another vehicle my heater functioned quite normally at minus 25F.

More news and thrills once I have this Mishimoto stat in my hand.

Mike