If the average temperature is 90+ degrees outside every single day do you think the car would run better without a thermostat??

I just want it running cool, even if the startup took a little bit longer to warm up...which i don't think it will since with the sun beating down my xjs will be well over 100 degrees everyday.

Just looking for some input, no idea how long it would take to heat up without it.

My only idea (which completely depends on the particular system ) is that if the coolant is flowing too fast then it wont have long enough to heat up or cool down

 

Don't do it !!

The rear disc on the V12 thermostats is important to direct coolant flow properly. Those with a better memory will explain the details.

Many who know much more about thermo dynamics, or whatever you might call it, have convinced me that the "...flowing too fast to cool..." theory is a comeplete fallacy.

What temps are you presnently running? If you have 88ºC thermos and you're running, let's say, 100ºC coolant temp, then removing the thermostats or switching to a lower rating will do nothing to help. It'll just take a few minutes longer to reach 100º, that's all.

Cheers
DD

 

ronbros will be happy to tell you why you shouldnt do it.

regardless of what you use to cool your XJS, its not gonna take long to heat up, being as it has virtually no mass surrounding the cylinder sleeves.


best thing you can do in the summer is run straight water and LOTS of water wetter. Jamey uses something from royal purple thats supposed to work better than wetter. forget what its called.

be advised that a lack of coolant will lower your boiling temperature, but since its a pressurized system, it wont lower it much. remember that your boiling point is higher than normal at higher atmospheres. so even straight water shouldnt boil till 240 or so.

 

Also bear in mind that, besides old fashioned overheating, improper coolant *flow* and air pockets have caused many a dropped valve seat on V12s. Air pockets in the heads will create hot spots even the the actuall coolant temp....in the areas where coolant is actually flowing....isn't very high.

Cheers
DD

 

any air in the system is bad. your engine is a metal to water heat exchange, so if air is keeping the water from making contact, is just gonna hard boil the head.

not to mention that any air in the system effectively reduces your atmospheric pressure.

 

The disc, if it is the same as the V8, closes off the bypass as the thermostat opens. The bypass is what allows the coolant to recirculate for faster warmup. Without shutting off the bypass, the hot coolant exiting the engine will take the shortest path, right back into the engine.

Not good(tm)

 

Correct- a fallacy. If the myth were true and the coolant is flowing too fast through the rad to dump the heat, it's also flowing too fast through the engine to absorb it.

There's also no benefit in running an engine cooler than design spec, contrary to another old myth. Install the correct thermostat and away you go.

 

now ill argue this all day. My grand prix will knock (pre det) during WOT pulls at running temperature. the cooler my grand prix runs, the cooler my delta's, the more dense my supercharged air, the more power i make. it might not make a noticable difference on a naturally aspirated car, but on a supercharged car, its absolutely night and day. my car makes freaking mountains of torque on cold winter nights. the power is unbelievable compared to a hot summers afternoon.

and also, it may not make a big difference on the XJS, but on my grand prix, both supercharged and NA engines have a coolant passage through the throttle body, which causes the throttle to heat up. on Club grand prix, weve dyno'd our cars with this passage blocked off and weve managed to score a couple of horsepower, as well as eliminating a little bit of knock retard (KR) on WOT pulls. before i supercharged my grand prix, i also noticed a big difference in WOT pulls when at ~200*F (or thermostat open temp if you will) and cold engine pulls.

now you might argue that it has no effect on the XJS as it is not supercharged and has no throttle body passages, but remember, even though it might not be effected in the same way (delta temps, throttle body passages, etc.) it is still an 11:1 compression engine, and even on 93 octane, these engines still knock and ping at running temps. lower the temperature, eliminate the ping, and run more timing.

thats performance 101.

the only benefit to running an engine hotter is fuel efficiency. a hotter engine has smaller tolerances between the piston and cylinder, less blow by, the overall volume of air and fuel is larger once its hot, hot oil is less viscous and less resistant to the oil pump and components allowing the engine to turn easier, your spark plugs will run hotter, etc.

we go out of our way to keep engines cool. if it didnt make a difference, then we would save a lot of money and time by not running electric water pumps (which can operate with the engine off) and by not waiting during cool down between 1/4 mile runs. also, intercoolers would be useless.

 

That would only be true if an owner's goals matched the design "goal".

If the goal is power, then keeping it cool is not a "myth". If the goal is component longevity, then keeping it cool is not a "myth". It is good engineering with proven results in the real world.

Running it hot is also good engineering - if the goal is fuel economy and emissions compliance.

Running without a thermostat may not be the right method of running cool, but there is nothing wrong with running cool provided it meets a goal.

Running hot may be your preference. It is not the preference of most knowledgable performance conscious enthusiasts.

 

i love it when i rant for 10 paragraphs and someone sums it up in 6 sentences. lol

 

Actually no- keeping an engine cool to avoid detonation is putting a band-aid on a more serious problem, whether it be required from a design point of view or from owner-induced problems. The effectiveness of reducing engine coolant temps to obtain cooler intake temps is minimal.

Getting back to thermodynamics 101, it can be easily demonstrated that running an engine as hot as possible will directly aid performance and well as economy, emissions and every other desirable parameter. Each BTU of heat rejected into the cooling system is energy that didn't aid in pushing pistons, in simplistic terms.

It is true that running an engine hotter than design can induce durability issues- but I'd like to see some stats demonstrating that running an engine below design set points aids in durability.

Thanks.

 

lol, **** just got real.

yeah. serious problem being heat. technically speaking, higher octane fuel is putting a band aid on the same problem.


the dyno says different. hell, even ronbros picked up 3whp from blowing a fan at his radiator during a dyno session.

so did you get your increased performance figure by running your car on a dyno as hot as possible. no, you didnt.

this statement applies quite well to steam engines.
who told you a combustion engine uses heat to make power?

the byproduct of an internal combustion engine is heat. the chemical reaction achieved in internal combustion engines is exothermic (gives off heat.)


ill give you a good one. those plastic plenum manifolds on GM 3800 engines and LSx engines melt after about 70k miles at factory operating temps. hotter running engines, such as my grandmothers bonneville fail after 50k miles, and colder engines, such as my GT have yet to fail after 100k miles.


ill give you a better one. you remember the engine wiring harnesses on the XJS? lol

 

No. The effect is very real in terms of intake charge. The effect is more apparent in forced induction engines, but it also applies to naturally aspirated engines. Furthermore, no matter that a solution might be a bandaid, if it fixes a problem, then it is applicable as a "field engineering fix". Not everyone gets to start with a fresh sheet of paper and a team of engineers. They do what they can with what they have.

That is an attractive proposition .. in simplistic terms. But only applicable if there is a fixed budget of BTU's and the rejection into the cooling system was limitless. Neither of these is true. In fact, from reading the OP's other posts, he is in the midst of increasing the BTU input.

Pulling the old diversionary citation trick again? The one where the challenger does not present any of his own citations to buttress his own assertions?

Fine, there are SAE articles authored by engineers from at least Gates. It is not necessarily just the long block. There are also hoses, belts, impellers, and other underhood components that live much better when not heat stressed. Not to mention oil which is happiest when warm but not heat stressed.

The point is that the manufacturer's design goals and constraints may not be exactly the goals and constraints of any other party. Therefore, a blanket, all encompassing statement such as is inaccurate. Especially when it is labelled with the dismissive sequiter "old myth".

 

Just to summarise the position from my experience, even if some of these points have been made already. Starting from a standard setup:

1. Removing the thermostats will cook the engine in short order, it could easily end up twisting the block and wreck the entire engine beyond repair. This is because the thermostats re-direct the flow when cold into the cross-over pipe and back to the water pump, thus entirely by-passing the radiator. Therefore, if the thermostats are removed AND the ports in the thermostat housings to the cross-over pipe are not blocked off, disaster is guaranteed.
2. If the ports are blocked off and the thermostats removed, in practice, the flow will be no more than if the thermostats were there and opening correctly, so no advantage.
3. If your car has a definitely good radiator, good (replacement) main electric fan or good (as standard) mechanical fan and viscous coupling, and good water pump, it should not over-heat in (say) 100°F, but there will be little margin at low speeds, in my experience.
4. If (3) above is true and you would like more margin on the cooling system, then the most efficient remedy is to improve the airflow through the radiators. Not sure which model you have, but if an HE Lucas car, move the second coil out of the airflow and move the horns one to each side out of the airflow. Believe it or not this gives about another 18 square inches of uninterrupted airflow to the radiator stack.
5. Personally, I advise a BIG electric fan rather than the standard mechanical one, as that can run full blast at idle in traffic.
6. The absolute best solution, once (5) above is done, I believe - but I do not think many other people have tried this, or even want to! - is to improve the airflow to the stack further by moving the number plate to the side and cutting a slot in the front bumper. I have a slot as big as the number plate was, but actualy, I think one about half that size would be quite adequate, in which case the plate can be between the slot and the indicator lamp (see photo). With slot, the entire cooling system became incredibly efficient and cooled down the car incredibly well after a stop in traffic.

If you want to try (6), just unbolt the bumper and go for a blast. I guarantee you wil be amazed at the difference in cooling performance. Everything, under bonnet temps, hoses, wires etc etc are noticably cooler.

Greg

 

I run the factory recommended thermostats in mine, and as M90 mentioned I use Royal Purple Ice (2 bottles) which dramatically lowered the temps, however you cannot use it with straight water. Or any "water-wetter" type additive for that matter. It will react with and corrode the aluminum in the block. Mixing with antifreeze prevents that from happening.

I also switched my cars manual fan to an electric and have it set up to come on sequentially with the small factory electric fan. The one I installed comes on at a slightly lower temp and can run even with the key removed from the car.

 

i dont have a front bumper at all, and i dont have to run a front plate here in WV.

ive also got a huge pair of twin fans off of a W body grand prix that will be going on in short order.

 

i know a lot of you say that removing thermostats doesnt help flow, but not allowing the coolant to initially heat up is going to let you run cooler for a while. and this could be achieved by simply drilling the thermostat.

 

I thought we were talking about coolant temps? The assumption that lowering coolant (engine) temps will also lower air intake temps by the same degree is false, see below. It is true that lower intake air temperatures will have benefit due to increased air density but the transfer of heat from the intake ducting or intake manifold as the case might be is minimal. Take a look at the post on the S-type forum about the intake elbow- in particular this post:

https://www.jaguarforums.com/forum/s...e4/#post507635

towards the end where the following is stated:

"When the throttle is fully opened however, air speed and airflow increase considerably. Typically, the inlet air speed of a 5.7L engine with a four-inch duct at full throttle is 34 feet-per-second, based on a volumetric efficiency of 70% and an engine speed of 3,000 rpm. Most inlet systems for every intake manufacturer for this engine are 30 inches or less. This means that the air in the duct of a 30-inch inlet length on this engine at the given rpm is 1/10th of a second—hardly enough time to transfer an appreciable amount of heat into the air stream on any system."
This can be applied to the OP's engine where the presumption of reducing coolant temp will lower intake tract temps by the same amount and therefore air temps by a similar amount. Both presumptions are incorrect.

Addressing a different point, it can be said that increasing coolant temps beyond design spec can induce detonation, no argument there. It can also be said that increasing compression ratio may induce detonation, as could increasing spark lead. If a given engine is NOT suffering from detonation, lowering the compression or retarding the ignition lead would both tend to reduce power and efficiency. This is obvious but similarly, if an engine not suffering any detonation, why would reducing coolant temp produce more power? The same amount of energy is available from each charge of fuel/air (accepting that the intake air temp has not been reduced) but a cooler engine will continuously absorb more heat rather than make use of it to produce power. The simplest analogy I can think of is heating an uninsulated house- the more heat that escapes, the more fuel it takes to warm the room to the desired degree. The sole purpose of burning fuel inside a combustion chamber is to heat the air to the highest possible delta temperature. The higher the temperature, the higher the cylinder pressure. Losing part of this heat energy to the coolant reduces peak cylinder pressure.

Regarding the durability aspect- it's easier to prove that something exists than doesn't. Using the present fleet of cars, we can measure how long they've lasted as both a baseline for comparison and as evidence that prolonged operation at OEM design temps does not reveal a trend of abbreviated component life. IOW- there's no obvious problems that need fixing.

Using the ubiquitous GM small block once again as another example, thermostat temps were bumped from 160 to 180 to 195*F over the years to keep up with pollution regulations and to take advantage of advances in coolant and oil technology. There was no accompanying reduction in any engine durability parameter. There's my line(s) in the sand.

Can you point me to a specific document that contradicts this? General statements that rubber and plastic stuff lasts longer when it's cooler are rather obvious in nature but again, if the field data indicates that there's no real problem, what's to gain?

 

i would like to know how and who decided that 1/10th of a second is hardly enough time to do anything. since our pistons travel up and down 60 times a second, thats effectively 6 times longer than amount of time that the charge spends inside the cylinder of the engine. sounds like an awful lot of time to me.


1/10th of a second is hardly enough time for my supercharger to increase ambient intake air temperature, to a final delta temperature of nearly 250*F, but somehow it does.

how fast is your blower pushing air across your heater core to blow hot air in your face? since the heater core is nearly an inch thick, and the air is moving about 5-10 feet per second, that translates to 1/60th of a second. and remember that your heater core is heated by..... you guessed it, the coolant of your engine.

your clearly a well read bloke, but not well practiced.

your view on this point is short sighted. your still only thinking in terms of intake temperatures. remember that your cylinder temperature will effect the temperature of the charge within 1/60th of a second at 6000 rpm. hardly enough time to transfer any heat you say? lol

anyways, your engine temperature is gonna effect the ambient underhood air before it even reaches your throttle body.


how bout you run your V8 at 200* and ill run my V6 at 150* and we'll see which one makes more power.

 

m90-

I've not responded to your posts directly because of your aggressive approach. That's not what this board is about.

If you're wondering why there's a dramatic temperature increase in air temperature in a supercharger, it's due to the act of the air being compressed. Simple as that, look up 'ideal gas law' and 'Boyle's law' as proof. If a person is not familiar with basic level physics such as this, debating more complex topics such as Otto cycle thermodynamics is rather pointless.

If you wish to question the amount of heat transferred into the intake ductwork, please contact the author of the document. He's the OEM and is far more vrsed and experienced than either of us. I have no reason to dispute his practical findings or the theory behind it.

Referring to a previous post claiming that a 3HP gain was achieved by pointing a fan at the radiator, and putting aside such a modest deviation is well within the range of standard deviation from one run to the next, it's more likely that the fan lowered the air intake temps somewhat, and had nothing to do with coolant temps. If the fan had lowered the coolant temps, the thermostat would have simply restricted coolant flow to maintain a constant temp.

Given that a 10*F reduction in intake temps gives a 1% increase in power output, a 3 HP gain on a 300(?) HP engine is quite possible and easy to achieve.