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Old 09-25-2010, 08:48 AM   #11
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Re: Bypass Thermostat


Bypass thermostats are being coming scarce for Fiat spiders. The last one I tried ( a Behr) caused the car to run too cold. Both International and Chris Obert have no idea what the temp rating is for the thermostats they sell. My Fiat parts book lists two bypass thermostats, one rated at 85 degrees C for older fiats and one rated at 90 degrees C for more recent years. The later temp rating is what I need.

I checked Autozone # 25592, on line, per your post, I found Autozone rates them at 192 degrees, which sounds perfect. However, the online info says it does not fit a fiat. Did it fit your fiat without any modifications? If you had to make modifications, what were they.

I have a 1984 Pininfarina, which is fuel injected and needs to run at 190 degrees F.


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Old 10-27-2010, 06:41 PM   #12
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Re: Bypass Thermostat

Yes the mentioned part number is what Autozone quoted me for my 1980 Fiat 124, it was in the stock system, no modifications, same with my 84 Volvo turbo, which also included a water cooled turbo.

The Volvo used another type of bypass system, I'd start the car, back out of the driveway, let the car roll one city block down hill, when I lived in San Francisco and by the end of the block, the needle would just walk right to normal.

The Fiat system is simple, Im shocked its hard to find those parts anymore, the last time I bought one was in 03 and I last looked up the part in 08. The car we did the mod on was a 1986 Toyota MR2, which would take almost 15 minutes to warm up, due to the radiator being in the front and the engine behind the driver. On 38 degree mornings, it would warm up in 2 minutes and give you heat, versus 15 minutes waiting for heat.

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Old 11-23-2013, 12:12 PM   #13
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Originally Posted by Scott View Post
The Bypass Thermostat will allow your car to warm up in 45 seconds to 2 minutes. How it works? It connects the upper and lower radiator hoses. The inblock thermostat is removed and the bypass thermostat sits inline on the upper radiaor hose with a "T" connecting the lower radiator hose. When you start the car, water flows around the block via the water pump, The engine heats up completely before the thermostat moves water through the radiator. When the thermostat begins to open it mixes radiator water and prevents shock cooling.

That's no different than the 'bypass' already built in to American engines for decades already. Not to mention hot coolant is normally circulated immediately when the engine starts. Adding a 3rd 'bypass' does nothing.
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Old 03-09-2015, 08:57 AM   #14
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My last three cars all have the t-stat on the lower hose. Works great.
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Old 01-15-2017, 09:11 AM   #15
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This bypass will cause longer engine warm up. a normal thermostat stays closed to keep the coolant trapped into the block and allow it to warm up. It stays closed until the engine is hot. At no time does any coolant go thru the radiator until the coolant is hot enough to need cooling. By circulating the coolant in your system it will take longer to heat up the engine as the coolant flowing around will lose heat as it moves.
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Old 01-15-2017, 03:02 PM   #16
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I spend so much time in EOC it takes a lot longer for my car to warm up, twice as far as it does with the block heater starting it off at 105 degrees F. Your heater will circulate water if you have the temperature selector on and I KNOW every Nissan Z car form 11/69 had a water pump bypass hose.

I do like the idea of a thermostat that controls the radiators cooling capacity and I use foam pipe insulation to block off my radiator. When it went up to 70F here, I saw 220 degrees on my ultragauge and pulled one of the 3 pieces of foam out. Ran cooler but my mileage dropped a little.

Packard used to have louvres that closed up in winter to restrict airflow and keep the engine up to temp and many new cars are doing this, but the risk is it malfunctions and causes the engine to overheat.

This thread is 10 years old LOL.
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Old 01-15-2017, 03:54 PM   #17
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Originally Posted by R.I.D.E. View Post
This thread is 10 years old LOL.
Are you suggesting it may be to late to help the thread starter

Years ago when it was easy to work on cars we used to use winter and summer thermostats. A ten minute job back then, they used to sell stats up to 205 F for winter and also slow acting ones as well. Lots of cardboard in front of the rad helped in the winter. Coldest temperature I ever started a car in was -49 F and the car never warmed up inside LOL

But engineers have designed engines with the best cooling systems and not something to really modify.

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