Thermostat question

[boxdogracing]

I have an 83 spider and would like to put the thermostat in the head. From what I have read the older cars were originally set up that way, but at some point Fiat changed to the external stat. I have also read that the external setup is recommended, but could not find a reason why. If this is possible would I need to find parts from an older car or is there a provision in my 2.0 head.

[MNspiderman]

I was wondering the same thing. I have the housing that goes to the head for the head mounted thermostat but the thermostat seem to be missing. Plus like what you said. Why is the external better?

[manoa matt]

The external thermostat provides a quicker warm up to opperating temp, thus reducing wear on the engine. Advantages of the in the head stat is that the thermostat is much cheaper, available at most auto parts stores and in a range of temps, also less hoses cleans up the engine bay.

To convert you need to cap/plug, or weld up the passenger side of the coolant "T" and you can still use the exisitng hose. Or for the early clean look, grind the water outlet so the older style upper rad hose fits over it, or source an early water outlet.

Most of the external thermostats offered by the vendors are Behr brand and are of the 90deg C spec. Older versions by Savara and Whaler are 80 deg C.

If you are worried about running hot, lowering the thermostat temp will not help much, it just opens sooner. You need a lower temp fan switch.

If you car is FI then you need to retain the coolant temp sensor. On some cars is located on the water outlet itself, while on others its located on the bottom of the coolant "T".

[FiatJim]

I'm going to tag along on this topic with my own question: what is the procedure to TEST to determine if it is working? Here in rural NY it doesn't get above 90 F very often and my temp gauge has only gone into the upper ranges once. So I am wondering if the thermostat is really working, or am I overheating (but not boiling over) and not just knowing it?

[So Cal Mark]

the external stats flow more than the in-head stats. As the motors got bigger, they needed better cooling. One major downside of the in-head stats is the 6mm bolts that hold the water outlet to the head. They do strip very easily

[bwilson27]

Thanks, Matt and Mark, for explaining this. I've also always wondered why there were different setups, too. I'll be sure to baby those 6mm bolts from now on!

[ventura ace]

I'm going to tag along on this topic with my own question: what is the procedure to TEST to determine if it is working? Here in rural NY it doesn't get above 90 F very often and my temp gauge has only gone into the upper ranges once. So I am wondering if the thermostat is really working, or am I overheating (but not boiling over) and not just knowing it?

If your thermostat wasn't working, your engine would definitely be overheating, your gauge would show it, and you'd be boiling out fluid. The fact that it's not doing any of these things tells us that engine coolant is making its way to the radiator, and the radiator is doing some cooling. You can confirm that by feeling the radiator and the hoses going to and from the radiator. If they are hot, then your thermostat is opening to let coolant flow through the radiator.

Now, back to the topic at hand. I got a first hand education on this matter last week with my new engine build, and it's something that I've been seeing all along with this car, but much more exaggerated with this new build (1.8L engine, with internal thermostat). The hotter the weather, the more steady and controlled is the temperature, but when the weather gets cool, the engine goes through transients where the temperature gauge spikes to hotter temperatures, then recovers after a couple of minutes, or I have to open the heater vavle to help bring the temperature down. Last week, I drove the spider to work, and when I left to come home, it was 107° outside (about 50 miles from the coast)! The gauge came up to 185° quickly as I started home and stuck there solid, until I got closer to home, which is affected by the ocean breezes, and the air temperature outside was only about 60°F. When I got in the cool air, the water temp gauge climbed fairly quickly to about 220°, and I opened the heater control valve to help bring the temperature back down. Temps came down quickly with the heater valve open.

Here's why: The head gasket is designed to have progressively larger passageways toward the back of the engine. This is because the water pump is at the front, as is the water outlet to the radiator, and the built in small water return port back to the water pump, all at the front of the engine. The temperature gauge sensors are toward the middle and rear of the head, and the water outlet to the heater core are at the rear. The larger water passages in the rear of the head gasket helps to force some of the flow to the rear, by restricting the easier flow path through the front of the engine. When the thermostat (keep in mind that I have the internal thermostat) is open substantially, it allows a large amount of coolant flow from the head, such that the progressive water 'orifices' in the head gasket are effective. However, when the thermostat is just partially open, as in cooler weather, then there is very little flow through the thermostat, and by the same token, very little flow through the head gasket ports, which means that the small amount of flow takes the shortest path up front and the water cavities in the middle and rear of the head are more stagnant, so the temperature tends to build up there temporarily, until the hotter water finally affects the thermostat and opens it up a bit to let more water flow. By opening up the heater valve, I am helping water flow to the back of the head (and passing by the sensors), and bringing the head temperature down quickly.

This is where an external thermostat proves to be better. With the external thermostat, there is high flow through the head and head gasket all the time, allowing the head gasket orifices to properly disperse the flow in the preferred proportions throughout the head. As the temperature starts to get warmer the external thermostat diverts some of the flow through the radiator to provide cooling, and the rest of it goes straight back to the water pump and back through the engine again.

The bottom line is that the external thermostat allows large flow of water through the head at all times, but the internal thermostat only allows large flow of water through the head when the water gets hot.

To correct the issue on my car, I put a 160°F internal thermostat. It runs very cool most of the time (about 170°), but still has the transients. Now, with the 160° thermostat, my transients only go up to 190° on the gauge, whereas with the 180° thermostat that I had before, the transients would go up to 220° unless I opened the heater valve to help get rid of the transient. I plan to switch over to the external thermostat at some point soon -- and I'll report back to tell you how the transients go away, I'm sure.

BTW, Hal and I did some controlled testing on this engine last year, comparing the internal and external thermostats, the heat up times and temperatures at several places around the head and radiator, and the temperature control while on test drives. We did notice a couple of transients on those test drives when using the external thermostat, but passed it off as maybe a little air still left in the system, but I know now that it was the phenomenon described above.

Alvon

[TulsaSpider]

Alvon, great info! Thanks so much!

[majicwrench]

A radiator can get rid of more BTU's IF the temp is higher. In other words, a cooling system is much more efficient with a 190 deg stat than a 160deg stat.
IMHO, you should run what ever style and temp tstat that came with the engine.

[Mathew26]

Also to throw in more more reason Fiat went with the external tstat for most of the cars.

Fiat with racing and testing found they were warping the heads on the internal tstat cars. The way the water flows and the amount allowed once opened wasn't working well for them. It comes down to the head is aluminum and the block is iron, so they were expanding and contracting at different temperatures.

Matt