What termostat to get...

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Apr 4, 2014 | 10:40 AM

stingraymax

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Racer

Joined: Aug 2003

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From: Belgium /

What termostat to get...

So I'm replacing my radiator due to a leak with a dewitts radiator and spall dual 11 fans.

My first question is what temp switch should I get to go with the fans ( 185 or 195 ) and then what termostat should be fitted ?

I have been reading some posts on here but can't get to understand what would be best.

The car is a stock '75 with ac and at but I am planning on getting a 383 installed somewhere next year.

Thanks

Apr 4, 2014 | 12:36 PM

MelWff

Race Director

Joined: May 2006

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The thermostat would be a 180 large mouth such as below.
The fan should come on so that it brings the engine back down to 180, so there is usually a on off temp for the sensor.

http://www.jegs.com/i/Stewart+Compon...FW1nOgodZH0AFA

Apr 4, 2014 | 01:56 PM

hugie82

Safety Car

Joined: Mar 2007

Posts: 3,652

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From: Bridgewater nj

I usually run my fan thermostat 5-10 degrees colder than the engine thermostat. That way you'll alway have the radiator with cooler water than the engine.

Apr 4, 2014 | 03:06 PM

AirborneSilva

Melting Slicks

Joined: Aug 2012

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From: Titusville Florida

I just put in that exact same Dewitts setup on my 76 last week. After installing it I asked the tech support at Dewitts if I should/could swap out the 195* sensor on the radiator to a 185*, below is what he wrote back to me:

"You could switch out the sensor to a 185 if you wish, but I would suggest keeping the 195 and switching your thermostat to a 160-170 instead. If the thermostat opens the system flow earlier it will allow the radiator to do most of the work before the fans come on. Is your radiator an original radiator? If so you would see a huge temperature change but switching the radiator to an aluminum radiator."

Apr 4, 2014 | 04:32 PM

REELAV8R

Le Mans Master

Joined: Apr 2011

Posts: 6,284

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From: Hermosa

Quote:

Originally Posted by hugie82

I usually run my fan thermostat 5-10 degrees colder than the engine thermostat. That way you'll alway have the radiator with cooler water than the engine.

If your sensor to shut off the fans is a lower temp than the engine thermostat temp, your fans are going to runs continuously once the engine is up to temp.

If your engine thermostat is 180* then the fan off temp should be above that to avoid continuous running.

IE. engine thermostat 180*

Fan switch range on 205* off 185* or similar.

Apr 4, 2014 | 06:06 PM

7T1vette

Team Owner

Joined: Jan 2006

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From: Crossville TN

Since you do not have a computer or other devices in your car/engine that 'expect' to see 195*F before functioning properly, you should be able to use a 180*F thermostat. And, since you will have electric fans on the radiator, I suggest that they be set to turn ON about 15-20 degrees warmer than the stat temperature...and that they be set to turn off at 10 degrees above stat temp.

Unless you are idling for significant time on hot summer days, your radiator should be able to handle all the work. When the engine is working hard or in very hot weather, the electric fans will then assist.

Apr 4, 2014 | 07:29 PM

wilesre

Instructor

Joined: Aug 2013

Posts: 103

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From: West Michigan

Quote:

Originally Posted by REELAV8R

Depends where your fan thermocouple (thermister?) is located. If it's in the thermostat housing, then you are correct. But if it's located in the radiator, especially if it's on the outlet side, then you could have a radiator temp much cooler than thermostat temp without the fans coming on.

Apr 5, 2014 | 01:34 PM

gcusmano74

Drifting

Joined: Mar 2011

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Quote:

Originally Posted by REELAV8R

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Apr 6, 2014 | 07:37 AM

stingraymax

Thread Starter

Racer

Joined: Aug 2003

Posts: 463

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From: Belgium /

Thanks for the info, so this sending unit would be a good choice if i go with 180 engine thermostat

http://www.summitracing.com/dom/part...0018/overview/

or

http://www.summitracing.com/dom/part...5099/overview/

But won't the last one be too "hot" ?

The 205 -185 units I can't seem to find them

Thanks

Last edited by stingraymax; Apr 6, 2014 at 07:48 AM.

Apr 6, 2014 | 11:02 AM

#10

REELAV8R

Le Mans Master

Joined: Apr 2011

Posts: 6,284

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From: Hermosa

Quote:

Originally Posted by stingraymax

Either of those should work.
When it switches on and off will be affected somewhat by where you place it. In the intake manifold will be a slightly different temp than say the top of the water pump.
I think I'm running a 200 -185 on mine with a 180* balanced flow thermostat, got the sensor mounted in the top of the water pump and it works fine there.
These balanced flow thermostat can be purchased at O'reileys they allow better water flow characteristics vs the typical style thermostats.
Fan switches are a bit cheaper on e-bay if you want to try that route.

http://www.ebay.com/itm/185-200-Engine-Coolant-Temperature-Fan-Switch-/201038943430?pt=Motors_Car_Truck_Parts_Accessories&hash=item2ecedad4c6&vxp=mtr

Last edited by REELAV8R; Apr 6, 2014 at 11:04 AM.

Apr 6, 2014 | 01:19 PM

#11

AirborneSilva

Melting Slicks

Joined: Aug 2012

Posts: 3,487

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From: Titusville Florida

Quote:

Originally Posted by stingraymax

Are you getting the radiator from Dewitts with the dual spal fans already mounted? If you are they temp sensor is already installed in the radiator just below where the water comes in from the water neck. The kit comes with everything you need to connect it up, great kit

Apr 6, 2014 | 01:58 PM

#12

stingraymax

Thread Starter

Racer

Joined: Aug 2003

Posts: 463

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From: Belgium /

Thanks for all the info, Unfortunatly I already had the new radiator when I decided to dump the shroud and go electric.

I am thinking of placing the fan switch or in the thermostat housing or next to it in the intake manifold.

Apr 6, 2014 | 02:43 PM

#13

cv67

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From: altered state

St. Jude Donor '05

Those locations are fine

Quote:

I suggest that they be set to turn ON about 15-20 degrees warmer than the stat temperature...and that they be set to turn off at 10 degrees above stat temp.

Apr 6, 2014 | 02:45 PM

#14

lionelhutz

Race Director

Joined: Apr 2007

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From: South Western Ontario

I'd say you've got a good plan. Your plan of using a 180* thermostat and a 185* off switch is good. FYI, there are switches that turn on at 195* and off at 185* to keep the temperature fluctuations to a minimum.

Apr 6, 2014 | 06:14 PM

#15

Rebelrob

Drifting

Joined: Jul 2009

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From: Dallas-Fort Worth TX

Per Dewitt,s the temp switch they mount can vary + or - 5 degrees. In my case with the Dewitt set up, my fans typically come on at 199-200* and off around 180-185*. The temp switch is mounted in the rad just below where the water neck hose connects as mentioned above and my Temp gauge sender is mounted in the intake by the water neck. So there is a few degrees water temp difference from the intake thermostat area vs the radiator where the temp switch is mounted. I have a 180* stat with a autometer mech gauge. And yes if your not careful, if you go with a cooler temp switch, your fans just might run more often or continuously.

Apr 9, 2014 | 03:24 PM

#16

stingraymax

Thread Starter

Racer

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Posts: 463

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From: Belgium /

Would fitting the temp sensor in line of the radiator hose be a better place, or won't that make any difference.

http://www.summitracing.com/dom/part...2283/overview/

Apr 9, 2014 | 03:48 PM

#17

REELAV8R

Le Mans Master

Joined: Apr 2011

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From: Hermosa

Quote:

Originally Posted by stingraymax

Would fitting the temp sensor in line of the radiator hose be a better place, or won't that make any difference.

http://www.summitracing.com/dom/part...2283/overview/

That would be about the same as having it in the thermostat housing if mounted in the upper radiator hose.
Keep in mind it is just another place for leaks to develop however.

Apr 9, 2014 | 03:53 PM

#18

mysixtynine

Burning Brakes

Joined: Dec 2008

Posts: 971

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From: Middlesex NJ

I have a 509 in my car. I ran the 27.5" from a 73 with dual spals dewitts radiator with the sensor in the radiator.

Dewitts says the fans come on at 195 and off at 175 with their sensor.

I run a 160 thermostat and my fans cycle nicely when sitting and almost dont run when driving. If I ground the relays and leave the fans on the engine goes to about 157 degrees.

Apr 9, 2014 | 06:56 PM

#19

donyue

Pro

Joined: Oct 2009

Posts: 523

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From: Calgary Alberta

I"m running a 427 Dart SBC. I put a 160 thermostat in with the Dewitts rad and Spal fans. The keeps the engine at about 180 to 190 which is about right for me.