yeah im not sure what he is getting at either. The "depth" of the swing depends on how cold you are starting at and the operating temp of the engine (which doesn't differ that much between cars).
This effect is also affected by whether the engine is all aluminum/iron or bimetal. bimetal is worse.

This is more or less why the stock metal gaskets fail, they weren't made to do this and fail easier than composite gaskets, which allow for more sliding of the head on the gasket surface.

other than the ****ty stock gasket i don't see anything particular about the d2 that is different than most other engine. My truck heats up pretty quick and stays the same temp.....unlike a certain jaguar i know

You guys are thinking about it the wrong way, its not the cold swing its the hot swing.

With the stock thermostat these engines can swing up to 240 at idle in traffic or when you shut the engine off after a long idle.

With the TD5 Thermostat the upper limit of the swing is around 200.

So the swing being referred to is the running temps swinging between 188 and 200 with a TD5 stat versus swinging between 198 and 240 ish with the stock unit.

Then add in any other issues like clogged rad and you can see how you could be on the edge of stressing the block and head joint with contraction and expansion. Not to mention running very close to overheating... I believe the stock heat gauge goes up from its resting place in the center of the dial at 240.

It seems to make common sense to keep the swing to a minimum and as low as possible for long term life of the engine.

Since people have been getting these 180 degree stats only in the last few years it remains to be seen if this extends the life of the HG significantly or not but it can't hurt.

torque to yield bolts become plastic instead of elastic when used. Clamping force is consistent when a bolt is tightened to plastic deformation. This is especially beneficial to aluminum heads as they expand and contract a lot.

In other words, when an aluminum head is fully expanded the clamping force of a torque-to-yield bolt is much closer to what it was when the head was cold than a bolt torqued into its elastic range. A bolt or stud that is still in an elastic state can move and its clamping force can change.

Common thought is that this stretching results in the bolts stretching along with the heads and giving a consistent clamping force, this is untrue. Clamping force rises, which puts much more stress on the bolt holes as the studs/bolts essentially tighten as the head heats up and then become looser as it cools.


Seems like everyones thought process is bigger badder studs that can be tightened more must be better........there is a reason studs were common place 60 years ago and all of todays engines use torque to yield

I have also seen tips on installing Disco cylinder heads about using teflon on the bolts and torque to the same settings on all the bolts instead of using the factory specs. This is wrong. The reason it is 15 lbs + 90 +90 is that turns of a bolt are much more consisent than torque. think of 15 lbs as defined for the bolts being "seated" and then the 90 degrees and 90 degress makes sure ALL bolts are tightened the same amount and share the clamping force. Telling LR engineers to **** off and recommending everyone to tighten to 50 ft/lbs or 35 or 80 instead is retarded. bolt torque is too dependent on friction to use on something as unforgiving as a cylinder head ( also much worse with different sizes of bolts = different amounts of friction), which is why this is now common practice.

It's the middle of the day and my mind is elsewhere, so someone school me if i am just brain farting.

I'm seeing a lot of people talking about stats and don't get it. How does a thermostats initial opening and full opening affect running temp??? A thermostat that opens at 5 degrees and is wide open at 10 will have the same running temp as a stat that opens at 120 and is wide open at 160. Obviously there is a threshold safe for an engine, you don't want it to open at 500 degrees because the engine will have long overheated.
But generally the operating temperature of a gasoline engine is 190-210 degrees.

the stock stat opens at 179 and is fully open at 204. Obviously it opens before the desired running temp because it needs to be fully open and opening before gets rid of any shock that would result from it taking a moment to start cooling the system. And because 179 is an acceptable running temp (if it were cold outside)

either way the running temp depends entirely on the cooling systems capabilities. less than 180 is regarded as less than ideal for the engine, so if the stat opened at 150 in the winter, the cold winter air would keep the engine at possibly whatever the lowest settings the stat opens. In hot weather the engine will continue to heat to whatever its cooling system can maintain, so all the opening temp does is relieve some stress from running up to operating temp and possibly past it until the cooling system has time to run the temp back down as well as allowing the engine to heat up. If an open stat was placed into a system when it was hot the operating temperature would be IDENTICAL it would just take longer to warm up, which is bad.

So unless we are all worrying about putting a higher temp stat in for the winter, or a stock one in for summer driving, wtf does installing a lower initial opening thermostat do?

people act like if they could get their hands on a 5 degree thermostat there car would run cooler. that makes no sense

sorry for the rant lol

I agree.
In a perfect world, the cooling system would be an infinite cooling sink.

This is a term borrowed from Electrical Engineering.

If we have a perfect cooling sink - picture a radiator where as
any heat thrown at it is turned into infinite cold - then the thermostat would remain mostly shut.

Consider a cooling system which does nothing at all - the thermostat
would stay wide open and the engine would overheat.

Our cooling system should be closer to the infinite sink.
If the radiator is new,
the fan clutch is new
the aux fan is working

Then we are approaching a cooling system which would return cooler coolant
and we would run steady state with no fluctuation in temp.

For any heat presented to the cooling system, the temp drop delta would be the same.

In the real world of course, this is not true.
Up a hill and engine heats up, air speed decreases, fan clutch increases air pull thru radiator - cooling system has greater heat presented
and has more air flow due to fan clutch fully engaged.

Temps will rise a bit.

With a bad fan clutch, plugged radiator then temps rise a lot.

Going down a hill, the demand for cooling is low. Engine consuming no fuel, generating no heat.

The engine temp falls to the limit of the thermostat closing

And there are then the large temp delta swings.

There is a reason why nuclear reactors are on a large river or ocean.

Infinite cooling sink.

This is fine in theory, but anyone who has changed out a headgasket knows the torques end up all over the place. Some need a breaker, while some barely need a regular ratchet.

Dweb has a lot of experiments, arguments and conjecture about this stuff.

Ok, look at it this way. You have no thermostat at all. You crank your Rover and it would slowly heat up and sit at probly 160-170 deg F in cool ambient temps (educated guess). If you have a 180 deg thermostat, it'll slow the flow of water until it heats up more, and elevates the temp to around 180 deg. The stock thermo raises it 215 or whatever. The idea is the cooling system should be designed to keep the coolant too cold, and then the thermostat raises it to a to a good running temp.

Two issues are that I believe our system doesn't cool efficiently enough. Period. In the summer with ambient temps over 90, the temp starts to creep up because the system can't keep up. his is where I think an electric fan would be better, or I'm considering wiring my aux fan to be switchable for hot days.

The other issue is the stock system is designed to induce rapid and wide temp swings. In fact, page 421 of the RAVE states "the cooling system used on the V8 engine is a pressure relief by-pass type system which allows coolant to circulate around the cylinder block and the heater circuit when the thermostat is closed. With coolant not passing through the radiator, this promotes faster heater warm-up which in turn improves passenger comfort."

Also note that it says "in cold ambient temperatures the engine temperature can be raised by up to 10°C (50°F) to compensate for the heat loss of the 10% exposure to the cold coolant returning from the radiator bottom hose." So the stock thermo automatically raises overall engine temp by up to 50 degrees when it wants to. Talk about temperature swings!

This is why I'm a fan of the inline thermo mod.

Yeah, there's a lot of good reading over there. Many dudes think the torques are high for the ARP studs, and have used lower values to good effect.

I personally think about all the metal on this truck, much of which seems to be a steel-butter alloy. And then I think about bolts that are supposed to stretch an extremely precise amount when most of the bolts on this truck just break.

And then I realize there's no way I'm using stretch bolts on my truck.

I'm convinced the main 'advantage' of TTY bolts is manufacturers don't have to torque HG bolts anymore. Just slap 'em in there and crank 'em down 90+90. DONE. It's good for them, but bad for us.

So I'm having a bit of trouble understanding this post - you swapped your HG at 93k with no head work, and now you are at 108k with no issues?

Did you truck overheat significantly which caused the HG failure, or was it just weeping coolant?

you are misunderstanding torques application.

just because it requires a different amount of torque to remove does not mean it has a different clamping force. The friction between the threads could be great, resulting in "more torque" but that doesn't mean the bolt is actually tighter against the part.

A rusted stuck hose clamp that isn't tight around a hose isn't any tighter just because it is hard to turn the screw