Overheating NA mx5 - Don't run without a thermostat!

Archives of Posts to the NZ MX5 List back in 2006
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MadMaz
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Overheating NA mx5 - Don't run without a thermostat!

Post by MadMaz » Wed Mar 08, 2006 12:15 am

Hi Mik

No, never run an engine without the thermostat. The thermostat also serves to
back pressure the flow of coolant throughout the entire cylinder head and
engine block, ensuring all hot surfaces are evenly contacted with coolant.

Without it, you get way over boiling temperatures and steam pockets within the
water jackets of the head and block in the region of No 4 cylinder & even No 3
- and yet the temp sensor located near the front will register a lower than
normal temperature. So you're fooled into thinking engine temp's O.K. while
you're merrily cooking away the rear half of the engine.

Water, especially under pressure, always takes the easiest path home - and
without the back pressuring effect of the thermostat that means the flow
bypasses the water jackets in the head and block around No 4 and even No 3
cylinder.

Seen it happen many times before - the end result in time is usually a sudden
increase in oil consumption and the blowing of blue smoke from the exhaust, as
the oil scraper rings in No 4 piston loose their tension due to abnormally
high heat in the region - and often the cylinder bores may become scored too
as the compression rings turn blue from heat and begin to break tiny little
pieces off.

Running an engine without the thermostat is a big no no.

Always put in a new one if in doubt.

Cheers
Mark
Firm Believer in 98 Go Juice - Go for it!

Bill Rehm

Overheating NA mx5 - Don't run without a thermostat!

Post by Bill Rehm » Wed Mar 08, 2006 9:05 am

Excellent explanation Mark, thanks for this.

Bill

Mikael Bjornstjerna

Overheating NA mx5 - Don't run without a thermostat!

Post by Mikael Bjornstjerna » Wed Mar 08, 2006 11:41 pm

Hi Mark,

My info and advice regarding overheating is forwarded from three (3)
independent Mazda Service Centers.
Three because I was on the road when having the problem and wanted to
be dead sure about what to do.
Needless to say, it worked out perfectly well and I later had a new
thermostat put in. My MX5 is a 1995 1,8.

Well, there's always a different opinion and you're probably convinced
that the Mazda people are wrong.

Cheers / Mik


Le 7 mars 06, ` 21:05, Bill Rehm a icrit :

[...]

MadMaz
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Overheating NA mx5 - Don't run without a thermostat!

Post by MadMaz » Thu Mar 09, 2006 12:24 am

Hi Mik

Let me put it this way. An opinion is just that. An opinion or just a
belief. My writing was not based on opinion, it was based on fact and what I
have actually seen occur on at least a dozen occasions over 25 years.

Sure, you may get away with running without a thermostat for a short while -
but not for an extended period - that was my central point.

It's important for people to know that the thermostat in an engine has been
put there by the manufacturer for a definite purpose.

It's not an extraneous nor unnecessary item - so it's important that people
know why it's been put there - should they otherwise be tempted to run without
for a long period - costing them a fortune in engine repairs.

Cheers
Mark
Firm Believer in 98 Go Juice - Go for it!

Grant
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Overheating NA mx5 - Don't run without a thermostat!

Post by Grant » Thu Mar 09, 2006 7:45 am

As a non mechanic I'm curious about the back pressure you mentioned. Is the
back pressure important during the warm up process to ensure no hot spots
occur so causing localised overheating or is it once the engine has warmed
up completely? I assume once the engine has warmed up and the thermostat has
therefore opened, there is then no back pressure.
Interesting info.

Thanks,

Grant.
Red 2006 NC Tiptronic
FIX A PC

MadMaz
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Overheating NA mx5 - Don't run without a thermostat!

Post by MadMaz » Thu Mar 09, 2006 9:51 am

Morning Grant

Geoff's quite right of course about the prime function of the thermostat not
opening until the engine is warmed up - then progressively opening until the
right temperature is maintained as water now circulates through the
radiator.

But a certain back pressure is still maintained even when the thermostat is
fully open - the size of the opening even at Full Open, is much smaller than
the hole in the cylinder heat or attached manifold it's mounted in.

It really is important to put a new stat in, if the old stat's function is
in doubt. Don't just take it out - you'll simply get a false, lower than
usual, reading on the temp gauge. Lower, because the flow through the
radiator is much increased - AND effectively the rad is also not having to
cool the rear half of the engine properly.

Here's just one example from the past I knew about and saw the end results:

* Mitsi Sigma 2.0 litre 1986 - Overheating. Guy takes out thermostat - hey
he's now getting a COOL reading! Leaves it out and lunches his engine 6
weeks later - on taking the engine apart there was serious damage to the
rings and bore of No 4. Guy REPLACES his engine & includes a NEW
thermostat - hey the car's OVERHEATING again!! Because the REAL cause all
along was a partially blocked rad. Put's in a new rad - now all O.K.

All he managed to achieve by taking out his thermostat was to give him a
false low reading - and he paid the price by leaving the stat out (he did a
lot of motorway driving which certainly didn't help) - costing him in the
region of $1,500 + fitting + GST for his second hand Jap import engine for a
total of around the $2,200 mark.

New thermostats for most Jap cars cost $25.

Cheers
Mark
Firm Believer in 98 Go Juice - Go for it!

Grant
Need, more, 5-ing, time....
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Overheating NA mx5 - Don't run without a thermostat!

Post by Grant » Thu Mar 09, 2006 10:07 am

I assumed that's what you all meant about the back pressure. I wouldn't want
to run without a thermostat anyway but wanted to get the backpressure right
in my mind out of curiosity. Makes sense to me. As you said thermostats are
quite cheap and besides, winter is coming on and I want my engine (and
heater) up to correct operating temperature as soon as possible.

Grant.
Red 2006 NC Tiptronic
FIX A PC

Euen
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Overheating NA mx5 - Don't run without a thermostat!

Post by Euen » Thu Mar 09, 2006 12:19 pm

Interesting to note that the temperature sensors on my 1800 are at the rear of the head.

Cheers
Euen
TG Sports, classic roadster - modern technology. NA1800, 99 head, 11:1 +2mm Wiseco pistons, Link LEM, Alloy f/wheel, JR headers.

Euen
I am quitting my job and going 5-ing
I am quitting my job and going 5-ing
Posts: 619
Joined: Tue May 23, 2006 9:42 am
Location: North Shore

Overheating NA mx5 - Don't run without a thermostat!

Post by Euen » Thu Mar 09, 2006 12:19 pm

Interesting to note that the temperature sensors on my 1800 are at the rear of the head.

Cheers
Euen
TG Sports, classic roadster - modern technology. NA1800, 99 head, 11:1 +2mm Wiseco pistons, Link LEM, Alloy f/wheel, JR headers.

geoff cotton

Overheating NA mx5 - Don't run without a thermostat!

Post by geoff cotton » Fri Mar 10, 2006 4:48 am

Textbook answer; "the purpose of a thermostat is to raise the engine to
operating temperature as quickly as possible, AND KEEP IT THERE"...OK? Many
modern cars have two way thermostats which actually redirect water flow; most
important that these are in place. Single acting thermostats just block off
the radiator until the engine gets to temp.Removal is not a good idea, but not
"life threatening" If your stat has a 10c piece sized disc on the BOTTOM of
it; DONT LEAVE IT OUT! cheers, Geoff. ('A' Gr. mech)

geoff cotton

Overheating NA mx5 - Don't run without a thermostat!

Post by geoff cotton » Fri Mar 10, 2006 4:48 am

Textbook answer; "the purpose of a thermostat is to raise the engine to
operating temperature as quickly as possible, AND KEEP IT THERE"...OK? Many
modern cars have two way thermostats which actually redirect water flow; most
important that these are in place. Single acting thermostats just block off
the radiator until the engine gets to temp.Removal is not a good idea, but not
"life threatening" If your stat has a 10c piece sized disc on the BOTTOM of
it; DONT LEAVE IT OUT! cheers, Geoff. ('A' Gr. mech)

geoff cotton

Overheating NA mx5 - Don't run without a thermostat!

Post by geoff cotton » Fri Mar 10, 2006 4:59 am

Hi Grant. In a cooling system,pressure is needed to prevent air bubbles
forming around hot spots in the water jacket, This forms an insulating layer;
just like the tiny bubbles you see in the bottom of a pot full of very hot
water. That is the main purpose of the pressure cap. That is also why you
should never remove the cap "just to check the water" when you are on a trip.
You release that important pressure, and it will not return until the next
warm up cycle. Also, antifreeze also removes the pesky little insulators.
that's why it is a very important coolant. Forget all about the freezing bit;
Anticorrode and cooling is what the green stuff is all about. Be kind to your
car and change it every 2 years, at least. Cheers geoff.

geoff cotton

Overheating NA mx5 - Don't run without a thermostat!

Post by geoff cotton » Fri Mar 10, 2006 4:59 am

Hi Grant. In a cooling system,pressure is needed to prevent air bubbles
forming around hot spots in the water jacket, This forms an insulating layer;
just like the tiny bubbles you see in the bottom of a pot full of very hot
water. That is the main purpose of the pressure cap. That is also why you
should never remove the cap "just to check the water" when you are on a trip.
You release that important pressure, and it will not return until the next
warm up cycle. Also, antifreeze also removes the pesky little insulators.
that's why it is a very important coolant. Forget all about the freezing bit;
Anticorrode and cooling is what the green stuff is all about. Be kind to your
car and change it every 2 years, at least. Cheers geoff.

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