Over heating with no thermostat
 

My RX7 is overheating with no thermostat in it. It also has the ability to turn water into chocolate milk every time I flush it out.

From the previous owner I think its a combination of rust and radiator quick sealant.

I'm pretty sure the water jacket is clogged, because I thought it would be pretty hard to overheat with no thermostat in it.

Is there anyways to access the water jacket with out taking the engine apart? Like maybe taking the water pump off?

Or if anyone has any ideas it would be much appreciated.

Video of it overheating
http://www.youtube.com/watch?v=Q84fZ3QFyhY

UPDATE: after this last fush the water was looking much clearer and I used radiator flush but still obviously overheated.

video doesn't give much info. how long does it take to overheat? is your upper radiator hose getting stiff very quickly with the engine cold? i assume the video was trying to show the coolant boiling into the overflow, which just verifies that it's running hot. you could have a bad waterpump, thermo-fan or engine coolant seals.

to replace the coolant seals the engine has to be torn completely apart.

Milky water means you have oil leaking into your cooling system somewhere.

It's not unusual and almost guaranteed you will overheat the thing with no thermostat. Because you then have too much flow through your radiator and not enough through your engine..

I think the milky water is steam and bubbles. I would think I'd see some oil in the water when it pools on the ground or in the water when I empty the radator but you could very well be right.

As for the thermostat I though I read that the only time you should take it out is on the track because other wise you will never reach operating tempetur. Plus I thought the water pump pushes into the block first and with no thermostat from the begining it would flow really fast.

My fan clutch is always connected so the fans always running. So I guess that leaves water pump or oil leaking into the coolant...

Thanks guys for replying..

That's not actually how it works. A closed thermostat will push all the water through the block. Otherwise it diverts a portion of it through the radiator. If there is no thermostat it simply flows a percentage through each until the flow/pressure drop relationship balances out between the two paths. Often that means more flow thorough the radiator than design and less through the block than design and less than is required to keep the car cooled properly. I run a stock thermostat on my race car and i never see over 210°F after 1 pass through the motor (stock temp sender location)

it will flow more but it's not the main reason why the engine runs hotter, it is due to the port under the thermostat not being plugged up when you remove the thermostat which bypasses the radiator. i have removed thermostats on some cars with little ill effects if you plug the hole.

milky water doesn't mean it is oil in the coolant, dirty water with lots of air looks like a milkshake also but where is the air coming from is the question? let the car cool off and start it while it's cold, if your upper radiator hose starts getting stiff after only a few minutes of run time then your water seals are toast. meaning pressure is being built up in the cooling system too rapidly, which can only be coming from one place.

you should really put the thermostat back in.

Ok so I started it and felt the upper pipe, it was soft and ply able for a minute or so. Hopped in and drove it around with boost for another six and a half minutes. By then the need was just over half way up. At 3/4th it seems to boil so I pulled in.Tube was hard as a rock at that point.

Thermostat back in hu? Ok let me wait for it too cool a little

I hate to be Debbie Downer but from my experiences.
Chocolate water/antifreeze etc... equals blown seals.
I know this will sound very scientific but; I'd smell it if I was you.
If you smell gas/oil then gas or oil is getting into your cooling system.
Its about all I can suggest.
My last fc was said to have sat for ten years and the reason the water was dark was because of rust in the water passages. There might've been a little, but when I cranked it; it looked like a water geyser shooting out of the radiator...
After I had bled the system as well as I could.

Slitherz your not being a debbie downer I'd rather get to the bottom and face facts. And the fact is that your right. I used a clean roasting pan from the kitchen this time and dumped the radiator and theres fuel in the chocolate milk.

Thanks so much guys for all your help. It looks like I need a rebuild. But for those 5 minutes I got to drive it before it overheated were awesome.. Felt good to drive an RX7 again.

Its going to feel good to rebuild it also LOL :nod:

You have to have the thermostat in, otherwise it will over heat. With out the thermostat in, the water is traveling to fast to pull any heat from the engine, there fore you overheat. The color of the coolant could indicate build up in the cooling system, oil in the coolant, etc.... Depends on how old the car is, if it has been driven everyday or not, and the condition of the system. Have you serviced the cooling system regularly???

Nothing personal, but this is misinformation. Clear lack of understanding of basic thermodynamics. Increased fluid flow in a heat transfer system (all else being equal) always increases the amount of heat transfer. Further the flow does not increase through the engine without a thermostat it increases through the radiator. There is less flow thorough the motor.

In the real world, cars without thermostats ALWAYS run hotter. Water does not stay in the radiator long enough to have the heat removed.

In no paper written does a no thermostat configuration get recommended unless there is a way to control pump speed:

http://www.eis.hu.edu.jo/deanshipfiles/pub10647303.pdf

I agree but not for the reason you state. The reason, again, is because the flow is reduced through the engine in a 2-way thermostatic valve system like the RX-7 (and most other street cars).

only this bloke has it correct,, the rest is rubbish
this is a bypass thermostat,, if you remove it you must thread a 1/2 NPT fitting into the bypass hole under the thermostat
-- or dont pass go
i have run without,, daily,, for years ,, summer here is past 100F ( 37C )

neat.. Post your data then. If you read the paper there were more issues then overheating.. Thermal control, etc..

you do know whats special about 3397-15-010B water pump housing dont you?

i will give you a tip,, factory race water pump housing,, no bypass hole ,, no thermostat

do you think they didnt know what they where doing???

yes, thermal cycling and warmup is kept to a minimum with the thermostat , reducing wear in street cars
cars run at hotter temperatures are more efficient,, requiring less fuel than cool ones

that is the ONLY reason it is there
with this restriction removed more flow in the same time period can happen both through motor and through radiator
( newtons third law,, conservation of motion / force suggests it can not be any other way )
[ how can it pass faster through the rad,, yet slow through the motor ??? :lol: ]
radiator and motor quench still occurs,, as the system still has pressure with a differential either side of the pump
( ie the motor,, on the discharge of the pump,, always has more pressure than the radiator which is on the suction side )
the thermostat thus is not required to maintain higher quench pressure in the motor than the radiator
at any rate,,,, the minimum restriction is still through that thermo seat part of the water housing
- it hasnt moved location




without the coolant thermostat--
--there is some symbiosis with the bypass thermostat that is in the oil cooler and coolant temps tended to settle around 90 C any-hows



in the same car,, ( on a 1.1 bar cap and with redline water wetter , s4 pump and ASI crossflow radiator , LTX ignition and LPG fuel )

fitted consecutively with firstly a normal mazda thermostat
- then the hi flow version,
- then the same with a few extra holes drilled around it
all ran at 97 C normal running temp and ran offscale ( on the LTX handset ,, up to as far as 240 F on the cabin gauge )
all this within 30 seconds of boosting the engine
--needing to coast substantially for quite some time at 90 + km/h to recover
--after shutdown,, it would still boil over
( all thermostats tested functional )


with the thermostat fully removed ,, this same setup runs at 90C
gets up to 97C with a good squirt
and then recovers MUCH more quickly and rarely boils after shutdown

clearly,, much more heat exchange is happening with more flow ,, retention time in the radiator is not the limiting factor ,, rather excessive retention in the engine is



-- this is daily driven,, through summer , tested on consecutive similar hot days with evolving setup over the same 30 km round trip
and i kept more than just a casual keen interest in the cooling performance

this year,, its evolved a little,, back to a 12a water pump
( easy to source cheaply )
-still blinded on the bypass
and this time,, a larger custom radiator ( been in there 2 weeks ) and the ignition has been reverted back to DFI dizzy
( ltx is gone in exchange back to wastespark DFI )
-- its only 25-30 C ATM ( spring ) but the motor has yet to warm further than 180F
( 82 C )

had it had a thermostat,, undoubtedly it would be running at the thermostat design temp
- either 82, 87 or 90 C depending on which one you fit


definitely a scenario where the car without thermostat runs cooler than one with---

i have evolved this cooling system enough that when before it struggled to stay on scale on the ECU to the point where it struggles to warm and make design temp
( flat top frontmount/V and flat mount oil cooler and very large single pass downflow radiator, all independent airflows )

- a case of now i can put that drilled thermo back in ( maybe come next winter )

Maybe something wrong with your setup? I could blast a 10 Sec quarter mile and incur no signifigant heating issues. Stock Mazda thermostat installed.

Far as the race theory goes, thats nice since they have big budgets and thermal expansion and contraction are not much of an issue.

I stand by my statement, I would not recommend anyone remove the thermostat save for troubleshooting purposes.

rat

remove thermostat
plug bypass hole
enlarge water pump alternator an eccentric shaft pulleys
relocate oil cooler further to the front
enjoy

p.s i dont build cars to drive for 10 seconds

But you do bump a 5 year old thread for no reason...

I wouldn't even remove the thermostat and plug the bypass on a 100% track car. Maybe I'm weird but I prefer my engine running at a constant temperature for things like maintaining clearances, ease of tuning, and on the street, fuel economy.

Thermostats don't overheat cars. Undersized or broken cooling systems do.

i think i agree, i've done it a couple times and the rotary cars run at the same temp, you'd never know the thermostat wasn't there, it just takes longer to warm up.

piston cars are funny, they just never warm up. when we dynoed the current miata, we did it without fans, and then we still had to let it run for a bit between pulls to keep temps up.

Years ago I was tuning a 13BT in a 1st gen on an original MS1. There were all kinds of issues with the car so tuning was day after day after day. But it was odd, it seemed every day the map would need to be completely different. This was in the last month of winter where the days were alternately below and above zero. After screwing with it I finally (don't know why it took so long) started looking at the temperature plot in the datalogs. Up and down, all over the map. Car was going into and out of cold start.

So I asked, has the thermostat been changed?

And the reply was: What thermostat?

Sigh.