No thermostat = runs hotter

Several times during my life people have told me that removing the
thermostat from a water-cooled engine will make it run hotter "because the
water moves too quickly to transfer the heat".
I have responded "bullshit" (or something similar) but it happened again
today and the feller saying it seemed pretty intelligent so I thought that
there may just perhaps be some principle that I don't know about (me being
ill-educated an' all).

Have any of youse heard this?
Do any of youse believe this?
Can any of youse explain this? (apart from "it's the friction of the water
causing the heat")

Thanks .....

 

Errmmm considering that the mechanics at work remove the thermostats in
vehicles that have mild overheating problems as a first check and a first
attempt at cooling them (before considering a different thermostat) I'd
have to say (much as it hurts me) that you are (arrrrgghhh) right... (phew
got it out!).


G-S

 

There was an Ian Irving tech article in a recent Rapid Bikes magazine where
he talked about a problem with a race bike that was over heating which
they'd tried (unsuccessfully) to fix by putting a larger radiator on. When
they called him in to diagnose the problem, he slowed the water pump down
and that worked. He talked about a concept he called "dwell time",
explaining that you can pump water through the radiator too fast, and it
doesn't spend enough time in it to cool down properly...

No personal experience though...

big

 

Nah mate, it's the friction of the block on the water.

HTH, HAND,

GB

 

Thermostats are put there to restrict water flow, keeping the water in
the head/block causing the motor to heat up quicker. Pulling the
thermostat out lets the water flow through the radiator with less
restriction, allowing more cooling.

As Geoff says, standard practice when a motor is overheating is to rip
the bugger out.

SteveB

 

I've heard of it and don't know the exact reasons why... but think of
it this way:

If it didn't need it, it wouldn't have it.

 

Heh - I know the difference here - mechanical engineers build weapons,
civil engineers build targets, right?

;-)

big

 

OK this sounds logical (especially the localised boiling).

It would also be less of a factor on a diesel than on a 4-valve alloy-head
so Geoff's mechanics probably don't need to worry much either.

 

It needs a thermostat in Germany. It probably doesn't need one in
Australia.

 

Arse about face in my experience. Jag engines tend to run hot, so
there's been a fair bit of experimenting, and removing the thermostat on
one is definitely a negative result. The OP gave a technical rundown
that I'm not qualified to comment on, but empirical evidence on one type
of motor suggests they are needed - dunno if you can extrapolate it to
all engines but def a bad move for a Jag I6 or V12

JL

 

Thats true, but the "both ways" aren't necessarily symmetrical. The motor
has bits like exhaust valve guides that have bits of metal at something
like 1000 degrees touching them[1]. The rate that the heat transfers there
is very different to the radiator which has a "cold side" thats only 70 or
80 degrees colder than the coolant...

big

[1] I have no idea how the heat transfer from the exhaust valve head,
through the stem and seat, and then on into the head and coolant works, I
guess we can get the same CFD weenies who're going to do your turbulent
flow analysis on the radiator to run that one through the software as
well...

 

Some water pumps tend to (some technical word for air bubbles impeding the
flow) but whack a Chev motor in it an' you'll be right mate!

 

Gemma_k wrote:

"Butchered"? That was a quite expensive Special Tuning Dept. part
which was then copied by various folk.

The chief gain, however, was to let you weld up the two stupid pipes,
between the head and the block, which required a wee hose to connect
them in an unmodified A-series engine.

regards,
CrazyCam

 

I don't think they 'worry' much now ;-)

The issue with diesels is somewhat clouded as they tend to be available with
a selection of different radiator caps as well.

G-S

 

Where I live it can (and does) get cold enough to wax (freeze) the diesel
(yes even winter mix, and they don't sell alpine mix any more to non alpine
areas). Something around -4 C happens a number of times each winter and -6
C isn't unknown, most time expect winter morning temps of around - 2C.

In summer high 30 C days are the norm with a good sprinkling of 40+ C days
and the occasional 45 C day.

Given this variation I think we _need_ thermostats... even if where you live
doesn't


G-S

 

Lack of cooling pressure lowering the boiling point is one problem. The
other problem is without the restriction provided by the thermostat, in
some engines the water flows preferentially around the cylinders
nearest to the water pump, and not around the ones at the other end.
This leads to overheating and blown head gaskets. As someone else said,
one example is the BMC A series engines as found in Minis. People who
race those put a plate with holes in it in the housing if they run
without a thermostat.

If it is necessary to run temporarily without a thermostat due to it
getting blocked or refusing to open, it is better to pull the spring
and seal out the blocked/non-opening one that you have and then put it
back in, rather than remove it all together.

 

I was thinking "cavitate" but that's when it's so impeded nothing's
happening.

Yeah no worries Ill balanced and no resale value, she'll be apples
mate <wink>

JL

 

Haha, and to think ... I just did a demolitions course.

And I don't even want to think about this subject too much. I don't like
theorising without sitting down with the calcs. Doh!

Cam

 

Ahh ... and CFD too ... you reading my mind or something? In any case, that
would mean I'd have to learn how to use CATIA properly to 3D model the
problem them import it across and start meshing it. Bah.

Cam

 

Diesels do not run cool and need a thermostat as much as a petrol engine.
What Gemma said is correct and, if I can add a small point, insuficient back
pressure on the pump will also cause cavitation, which will reduce the
amount of water being pumped, cause local boiling, and destroy the pump
bearings in no time at all. From cold, a missing thermostat will extend the
time taken for the engine to get up to operating temperature, seriously
increasing engine wear.

Geoff, you need some new mechanics.

Theo