I THOUGHT I had a good understanding of cooling systems and how the stat functions within them... but BOY... did I just learn a few good lessons... and shattered some well worn beliefs I once had...
I also know some of youse guys BELIEVE in some of the FALSE PROPHETS I once did... maybe for different reasons...but I thought I understood the Gospel... and I was way off the straight and narrow.
Below is a 1979 Factory Stat with 156,800 miles on it.
Here are two more... the one on the left is a POOR choice for a replacement... and the dual action one on the right is a GOOD choice as a replacement... Boris submitted these.
What I learned:
1. A good operating (180) stat will keep an X1/9 operating between 185 and 195 degrees as measured at the head... and will hardly vary.
2. A single action stat like the one on the left in the second foto is like taking two leaps backwards. The X has a great little recirculating system between the reservoir and the engine... The single action stat just eliminates this idea and undermines the original design and intent.
I kept my X cool at 185 idling for 30 minutes on the recirculating system... Then I pressed the engine and finally got the temp up enough to SLOW the recirculation and OPEN the gate to the radiator... supplying bundles of coolant. It was all I could do to get the fans to cycle on and off... (I had to... 'cause I wanted to make sure they WORKED!) It was about 70 degress out!
3. Opening the heater valve and turning on the fan... can, and once did, decrease my operating temp by about 20 degrees, almost instantly~!
Guess what? This neat little trick can help... but also indicates your stat is NOT functioning properly. Actually... it usually means it isn't SHUTTING DOWN so that the water can have time to pass slowly through the radiator and COOL. Now that I have a good stat... Opening the heater valve and turning on the fan may dip my guage a few degrees... and then the GOOD stat shuts down the flow... causes more recirculation and keeps the engine temp UP to 185! Hmmmmm! Boy, was I surprized to figure this out!
4. I'm still sure the Duralube in the crankcase is a big help at reducing friction... and thereby assisting in keeping the engine relatively cool. I once believed it was the the premiere savior... and all along I was in need of a good stat. Otheres have also stated that Synthetic Oils can do the same... and I think they are the way to go.
5. Our specialty venders, I am sure can get you good operating foreign replacements... My local parts store had a dual action Stant (45378) handy and I grabbed it... they had another number also... but I bet it was a single action stat... anyway they didn't have it and I was satisfied with this one. Cost was about 12 bucks.
6. When I tested the old one (first foto) against the new one... I used a cooking thermometer and a pan to boil them in water. I put them both in the pan and watched my pot come up to temp and at 180, BOTH stats started to open... with the old one opening FASTER AND FARTHER... than the new one was even capable of!!! Hmmmm! I figured that mess I took out was most likely STUCK closed... the gasket was crap and was probably leaking by too...
Anyway... the REAL DIFFERENCE was when I took them out and allowed them to cool on the counter... and I watched and watched! The new one was quick to close... and the old one just hung open forever... and then eventually closed.
I am convinced that this allowed the coolant to flow too fast and NOT get the time to cool. My 300 mile run up and over the Grapevine and back was proof to me that this new stat made all the difference in keeping my engine at proper operating temp.
I submit all this for your consideration... and keep enjoying your ride!~