74C Thermostats

[Darkspeed]

They use it because they have to compromise - provide good ecomony emissions and effective heating and compensate for fuel atomisation etc etc etc. - they have a completely different criteria to people just looking for maximum power potential.

70C is just fine for looking after your engine an oil and treats the oil even better - As for me its changed every 2000 miles anyway

Heat is Energy - What make you think that running a car at 70C is more wasteful than running it at 80C?

Anyway - I'm done here - number for 74C stat for RV8 above if anyone wants one.

Cheers

Andrew

Hmm, so why does every car manufacturer in the world use a pressurised cooling system, that runs well above 74c?

How long before you have emulsion and goop in your oil if your motor never warms up properly?

I've always thought that heat is power, and sucking heat from your motor is just sucking power out and dumping it in the atmosphere.

[kiwicar]

The conclusion I have always drawn from the Vizard test, 5.0 ford turbo v8s, porsche race engines and suzuki engines and is as follows
1/ the heads want to run cold as possable, 68 to 74 C so you
a) delay detonation as long as possable
b) keep the fresh incomming charge as cold/ dense as possable
2/ run the bottom half of the engine at around 85 to 90 C but most of all at a constant temperature so that the bores
a)get properly lubricated
b) you don't have to run too much taper hone so the rings are stable
3/ run the oil hot so it is properly up to temperature and is at a lower viscosity so
a) you use less power pumping it around
b) the oil is at a constant viscosity through out its path around the oil galleries
c) all the bearings are nice and loose as they are at a higher temp

I have drawn these conclusions from drag race ford 5.0 v8s that are either running parcially filled blocks and a reduced block cooling system and seperate head cooling, or where they run fully filled blocks and head cooling only. Porsche race and road engines that used water cooling to the heads and air cooling to the cylinders. Suzuki gsxr engines that did the same but with oil cooling to the heads (seperate to the sump oil system) and the dave Vizard tests described before.
This is further confirmed if you look at the design of many high performance heads where the inlet port comes in at a very steep angle into the head and hve the waterways extending up the sides of the ports all to keep the inlet charge cool (and obviously giving a good shot at the back of the valve)
As I said before it has the down side of tending to lead to poor fuel atomisation and fuel pooling (especially on carbs) but is less of a problem with high pressure electronic fuel injection.
I also think the problems of the 4.6 being "run too hot and too lean" is not the whole situation I think it is also related to the way the later blocks put the loads from the heavier large journel crank into the block and probably heating and cooling cycles of the whole engine.
I would certainly run a cooler stat in Aus, especially in the summer, the cooling system has alot more to cope with in the much higher ambiant temperatures there, but over here in winter I would worry about the oil not getting up to operating temperature.
Mike

[HairbearTE]

Generally because temperature robs power - good for economy but not much else - Anything above 70C and power drops off the hotter it is and the more the power losses -

The 74C stat is a compromise on a road car as the temperature usually settles about 4C over this.

Question is why would you run it hotter?

Hmm, so why does every car manufacturer in the world use a pressurised cooling system, that runs well above 74c?

How long before you have emulsion and goop in your oil if your motor never warms up properly?


I've always thought that heat is power, and sucking heat from your motor is just sucking power out and dumping it in the atmosphere.

The reason all modern production engines run much hotter than this is emissions regulations, which get tougher all the time of course and are easier to meet running a hotter engine.

[v8man]

and as emissions are tougher they are runing hotter and hotter and components are startying to melt and others giving up the ghost and on my case alternator not charging when engine at full temperature and by adding a heat shield to de alternator problem sorted lol
and my rover v8 4.8 litre running a low temperature thermostate so water is no hotter than 80

[Paul B]

The reason all modern production engines run much hotter than this is emissions regulations, which get tougher all the time of course and are easier to meet running a hotter engine.

So all we hot rodders and old car modifiers trying to seal cooling systems and run pressure caps are really wasting our time, and unless we get checked for emissions at MOT time we're better off using an open system and a cooler 'stat?

[kiwicar]

Try again
If you are building a race engine and you are on the edge of detonation and the engine has been designed to run cooler by having more taper hone on the bores then running cooler heads will stave off detonation a little longer and use a tad more timing and a slightly denser mixture and you will get more power.

However

You risk pinching the piston skirts if you run it too cold, your Idle and part throttle could/will be effected you will put more fuel out the exhaust unburnt and you risk damaging your bearings if the oil does not heat up properly as a result.

In a hot climate with high inlet ait temperatures then this can be a good way around the short comings of the cooling system, you won't have the problems with atomisation as the 29 to 32deg C dominates the situation.
Rover have spent alot of time and research into which thermostat should be used in which enviroment, 82C in europe where it is cold, 74 C in Australia, I would think carfully before you change it and understand what you are doing to the whole engine.
If you are building an all out race engine than block temp is somthing to think about, as I said before it has been used by drag racers and car manufacturers to get a few more bhp but also it seems that what is actually mneeded is a split system to keep the heads cold and the bores hot.
Mike

[Ian Anderson]

A quick question here
Water flow in the head / block which way around is it?
Into block and then back out through the heads or into the heads and back through the block?

From Mike's explanation I would presume into the heads - would cool the heads more and then through to te block where less heat could be absorbed into the already hot water.

Thanks
Ian

[RoverP6B]

Hello Ian,

It is my understanding that coolant flows through the block first, then enters each cylinder head at the rear of the engine, flows through and exits at the front...then flowing into the inlet manifold, feeding the heater matrix if fitted before returning to the radiator.

Ron.

[v8man]

another thing i got a 2003 vectra with 130000 no probs only oil changed every 20 k,my neigbour has a safira same engine 60 k most driven in town and it smokes and all ways problems,
mine driven motorway 90 % in town 10%
in town temperature gauge on 90 all the time on motorway goes down to 80
if is better for the engine to run hotter y is that then they run cooler on motorways and on open roads for sure car makers would ensure they would run hot all the time no ?

[Robrover]

I run a 74C 'stat in my 4.6 SD1 with Edelbrock carb and a three core radiator. My 1360 Mini runs a 71C with Water Wetter, four core rad and an oil cooler. On the Disco it's 88C with the Hotwire and this has to stay as I believe the enrichment doesn't cut out till the temp reaches 80C. Anything less and the ECU just throws in more fuel.

[kiwicar]

Ian
rover and Gen1 SBC and alot of other older design engines are block first heads second, the LT1 Gen11 chevy has a "reverse flow" cooling system (it is about the only real design change from the Gen1) and it cools the heads first. Gen111 (Ls* series)is heads first. More modern engines are heads first block second.
V8man
The Vectra is the clasic short journey bore washing problem with where it never gets off cold start enrichment probably added to this is a case of cold oil.
I bet it actually was never run in properly, probably just driven on light throttle 3 miles at a time, never given any proper miles so the rings never bedded in and it has neverbeen up to operating temp. We had a vectra from new, were told by the garage to "take it for a good run as soon asyou can, these engines like a good thrash when new" so its first 420 miles were a straight run down from Glasgow where we bought it to Wendover, the engine was always very good on that car.
Mike

[Ian Anderson]

Mike

that is what I thought - block first and then heads

So for us modifiers would it not be beneficial to change to something like a electric pump and force the water the other way through the system?

This would then get heads cooler and block hotter

Just a ? a bank balance has to recover from some house works!

Ian

[kiwicar]

Yes ian
for us chevy boys it it a change to an LT1 water pump if you are running a crank driven pump, I am planning electrical however as I will be running dry sump oil and a vane vaceum pump and an alternator below the crank centre line. I am certainly intending to do heads first cooling.
This also leads to the benifit of coating the heads and ports in some heat reflecting/ insulating coating, haven't done it on mine as I am relying on the basic spec to get me the power I want, however If I start looking for a few more bhp it is one of the first things I will do after a CNC port on the heads.
Mike

[topcatcustom]

If you were to change the flow direction on a RV8 surely it wouldn't work properly? Trying to pump hot water downhill etc, then crossing over the feeds into the rad wouldn't be ideal, all this is related to why it is important to have the top hose dead flat or flowing slightly uphill into the rad isn't it?!

TC

[katanaman]

all this is related to why it is important to have the top hose dead flat or flowing slightly uphill into the rad isn't it?!

TC

All this solves is the chance of getting an airlock in the top hose. If you have a bleed in the hump you wont have any problems with up down top hose.