Replacing my Holley t-stat

[Vermonstah]

Howdy to all!

I will confess that it has been a while since I have been here on the forum. Life (aka work) has been occupying too much of my time of late.

But also, my engine has been running strong and reliably!! Thanks greatly to the incredible guidance and advice that I have previously received from Moyer and here on the forum.

But, it appears that my Holley t-stat has finally given up the ghost. As in, the "cap" which mates with the housing when opened, that cap has broken free from the body of the t-stat.

SO, short of an attempted repair, time to replace the t-stat after more than half a century of faithful service

But replace it with what? Unclear to me from the catalogue what Moyer now recommends. And yes, I have both a call and an email in to Ken to garner his counsel.

Though I realize that it might constitute as sacrilege to post such an inquiry here, just wondering if anyone has positive experience with the aftermarket t-stat modification from Indigo? I am intrigued by the design and the advertised benefits

And for context, I have a RWC late model. I also previously replaced my t-stat housing with Moyer's bronze housing.

Thanks for any insights.

[Dave Neptune]

Matter of choice

The new double acting t-stat that our host designed and offers is a good quality product.

The products that Tom offers at Indigo are also good quality products.

It's just a matter of choice and maintenance convenience, IE ease of access due to styles that would influence my choice.

Personally I used a bypass valve for 34 years and that too worked just fine.

Dave Neptune

[Vermonstah]

Dave - thank you for the timely insights.

I managed to catch up with Ken today on the phone. After a brief discussion confirming that my Holley t-stat has indeed given up the ghost, I placed my order for the MMI double-acting t-stat.

I will update this thread with a comparison of operating temps between the two different t-stats.

For reference, the Holley t-stat kept the operating temp between 160 and 180 F. On the cooler side early in the season when the raw water temps run below 60 F and the operating temp might touch 180 F if I am continuously applying a heavy load to the engine, say in a significant chop.

And one more plug here. I simply pull out the Moyer maintenance manual in the Spring and Fall. I follow it to the letter. It is so simple, even I can do it. And then my A4 rewards me with reliable performance. Despite weathering some pretty harsh winters here etc.

I cannot say enough good things about the assistance that I have received here over the years. From Moyer and this forum.

Thank you all!

[ndutton]

Did Ken mention a replacement thermostat housing too? The fit on the thermostat bypass spud into the housing port under the dome is important for efficient function and if your housing is also half a century old I'd bet money the port has suffered some degree of deterioration. As we are fond of saying around here: do it right, cry once.

[Vermonstah]

Did Ken mention a replacement thermostat housing too?

I replaced the t-stat housing a decade ago to ensure that I was getting the most from my Holley.

[ndutton]

For comparison here are pictures of the bypass ports on my old and new thermostat housings. I didn't measure anything at the time but looking at the pictures the new housing port looks smaller.

[Vermonstah]

Updating with good news

As I mentioned above, my original Holley t-stat finally gave up the ghost.

So, I called Ken and ordered the "MMI Thermostat, 150 degree (late model double-acting)." Along with some additional t-stat gaskets to have on hand and some additional bits like a replacement impeller etc.

I popped the new t-stat in place, and fired up the old beast. At idle on the pin, quickly warmed right up to 150 degrees, at which point the temp continued to increase but at a decreasing rate. And then I throttled up to encourage the temp to rise to the top of the typical operating range. Which for my engine is around 180 on the temp gauge, slightly less approximately 174 with a laser on the temp sending unit.

This is the sweet spot for my engine, plugs are nice and clean at that temp. Dirty with excess carbon at lower temps.

So, there you have it. Another good news story, thanks to MMI and the insights here on the forum.

And from here, I don't intend to overthink anything. Instead, I will continue to keep things simple, religiously following the MMI Service Manual which has served me well.

Thanks again and best to all!