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Old 10-14-2007, 07:42 PM   #1
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Bypass Thermostat

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.

With a conventional thermostat, hot water sits behind the thermostat and builds up in the head, slowly the thermostat opens and has to heat the entire cooling system before all the water heats up. This leads to long warm ups and a cold engine wastes fuel. Not to mention, in winter you have to wait for the entire radiator to warm up before you get heat in the car.

This is a Fiat part, they used to be $16 at the local Italian parts store, the company has since subcontracted out the part and it is available at Autozone, part # 25692, $50.00 or online at International Auto Parts #3446 at $39.95. If they can't find it, tell them you want a bypass themostat for a 1980 Fiat 124 Spyder 2 litre DOHC w. fuel injection.

Now this little device has been on many European cars since the late 60's. My Volvo and Ford 2.8 V6 had them internally in the block, it was great, quick warm ups save gas. Also the only American manufacture I know of to feature a bypass style thermostat was the mid 90's Corvettes. They had a double reverse flow thermostat system, water was pumped in over the heads first, then went down to the cylinders. Water circulated around the engine first, then was plumbed out to the radiator. From what I read, the Corvettes heated right up with very little warm up time.

Like I have said before, why haven't all the manufacturers gone to the bypass system? Cost, 1 million cars with a 10 dollar thermostat saves more money than 1 million cars with a 40 dollar thermostat.

Now having been a convertable small car enthusiast for years, I have owned a Fiat 124 Spyder, as well as other little sports cars. What they say about Italian cars is false, they are just as relaible as all the others cars out there.

The bypass thermostat is genious, the little device can be fitted to any 4 cylinder with a maximum of 2 litres. It is a little cylinder that looks like a "T" or a jarge jack, three radiator sized outlets come off it and inside is a thermostat. You have a choice between 180 or 192 degrees. The only mods would be to take the stock upper and lower hoses and cut 2 inches out of them. You can insert the bypass themostat in the upper radiator hose, you will have to make a "T" in the bottom hose. I used a copper T I got from Home Depot, there is a T available through Italian parts dealers that is iron. Now the bypass hose is the same diameter as the radiator hose, what I did was go to Autozone, they let me browse through their hoses till I found one that was straight enough to connect the 2 ends, I forgot the part number.

Put the whole thing together and enjoy quicker warm ups, heat, and save gas.

I don't know if bypass thermostats were made for larger engines V6's or V8's The overflow bottle has been incorperated as a part of the pressurized system on newer cars, so you'll have to map out your cooling system before you do the conversion.

I will definetly put one on my next car.
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Old 10-14-2007, 08:12 PM   #2
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Why the pancake bunny?

It seems like an interesting idea, I hope you get some results.
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Old 10-14-2007, 08:16 PM   #3
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cuz that description of how a conventional thermostat works is whacked?

perhaps this will help:

http://www.familycar.com/Classroom/CoolingSystem.htm

although chuck must not be familiar with Ts.
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Old 10-15-2007, 10:19 AM   #4
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Ya know I just love your pancake bunny every time I see him. I hope you continue to keep him around.
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Old 10-15-2007, 06:33 PM   #5
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Anyways...

So, Anyways...

Would this bypass thing really help warm the engine quicker? I'm especially interested on those COLD Winter soaks that takes almost 15-minutes to get up to normal temp. (FE Killer, as I'm sure we know)...

RH77
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Old 10-15-2007, 10:54 PM   #6
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D'oh

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Originally Posted by theclencher View Post
the link, rh. the link

basically this guy is proposing to duplicate what is already there, except externally.
Yeah, I checked out the link, definitions, and schematic. It didn't sink-in that the existing system was already handling the task -- I guess I had to think about it...where is the water pump pumping the water with the 'stat closed? Exactly. I see know and understand the pancake bunny.
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Old 10-15-2007, 11:11 PM   #7
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Quote:
Originally Posted by rh77 View Post
So, Anyways...

Would this bypass thing really help warm the engine quicker? I'm especially interested on those COLD Winter soaks that takes almost 15-minutes to get up to normal temp. (FE Killer, as I'm sure we know)...

RH77
As theclencher mentioned --- just about every single car on the road today will already have a bypass line... The reason for the bypass line is to make sure it doesn't warm up too fast followed by a flood a icy cold coolant when the T-stat partially opens...

As for warm up times.... Without increasing the heat going into the coolant - you really won't heat up any faster. As it stands now, you're limited by the thermal conduction coefficient of aluminum and coolant. I guess you could attempt to make an exhaust<-->coolant heat exchanger... That would be troublesome once it's warmed up though....


VW (perhaps other automakers too) uses a oil <--> coolant heat exchanger.... It heats up coolant faster -- and then keep oil temperatures stable once warmed up Unfortunately, it screws to the head and is integrated into the filter assembly -- so it's not so easily adapted to other engines :/

Of course, the Prius has to be "different" (in a good sort of way) -- Toyota has a 1.5L thermos (or was it 3L?) type container that pumps hot coolant in when the engine shuts down and then pumps warm coolant back into the coolant system on start up. Given it's a vacuum insulated container - coolant stays hot for something like 12 hours and warmish for up to 36 (pulling these numbers from memory mind you).

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Old 10-16-2007, 03:10 PM   #8
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wish all cars had the thermos bottle
I'm with ya there. After shutting down the Prius, I recall hearing some activity still going on as I walked away -- probably the "Thermos Pump". Overnight, it was tough to discern if it really retained much heat, but after parking for a shorter time, it was warmed and quicker to reach the next "stage" of efficiency.

Most appropriate for my application though, is to get the engine and transmission fluid warmed-up from an extended parking duration. This Winter, I definitely will be improving on the cardboard grille block. It was tough to hang on to normal temps last Winter -- new stat and everything. Too much airflow over the fins.

RH77
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Old 10-16-2007, 05:00 PM   #9
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Quote:
Originally Posted by trebuchet03 View Post
Of course, the Prius has to be "different" (in a good sort of way) -- Toyota has a 1.5L thermos (or was it 3L?) type container that pumps hot coolant in when the engine shuts down and then pumps warm coolant back into the coolant system on start up. Given it's a vacuum insulated container - coolant stays hot for something like 12 hours and warmish for up to 36 (pulling these numbers from memory mind you).

The capacity is 3L for the thermos. The coolant will stay slightly warmer than ambient temp a couple of days. Also, it only seems to keep the coolant at ~130F overnight. When I've had the EBH plugged in, the SG will show a temp of 150F but will drop to 130F when the valve to the thermos opens and the coolant is released but it recovers back to 150F in a few seconds and will reach 160-170 within 1/2-3/4 of a mile.
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Old 10-17-2007, 09:12 AM   #10
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trebuchet wrote "VW (perhaps other automakers too) uses a oil <--> coolant heat exchanger.... It heats up coolant faster -- and then keep oil temperatures stable once warmed up"

Coolant heats up quicker than oil, so the oil/coolant heat exchanger works to heat the oil quicker during warmup, then keeps oil temps stable once warmed up.

I was thinking of adapting an oil/coolant heat exchanger onto my car. Later versions came with one, so it's a bolt on affair. It's attached to the oil filter housing with two nipples for coolant, so routing the coolant lines is easy. I'll check and see if it's adaptable to other cars with similar size oil filters.
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