SBC350 sticking Coolant Thermostat- drill hole???/ new brand recommendations?

[BlazerBill]

Quick question. GM crate small block Chevy SP350 385hp/aluminum heads/mechanical fan. My GM (factory) 180deg coolant thermostat is sticking closed and almost caused my upper radiator hose to burst. For a quick fix, I just bought a Murray 180deg T-stat from Oreillys until I can get a better quality one from Summit. I was considering a Robert Shaw FlowKooler T-stat. What’s your recommendations? Also, I thought I had found an older post about drilling a small hole in the T-stat but couldn’t find the post for details. Should I drill a hole in this Murray in case it doesn’t open or open properly? If so, what size drill bit or other instructions should I follow? Thanks!

 

[xm20k]

There are 2 styles stock type and a high flow version both made in various temp ratings, they are all made by like 3 companies most brand names are just re branded units not worth spending 60 for a unit that's sold under another name for a 3rd the price. Put one in run it up to temp and make sure there's flow thru the rad. They either work or they don't. If it consistently runs too hot and everything else with the system is good drop to a lower temp.

Pardon Our Interruption

I've never had to drill holes or modify a T stat even on race engines. I've ran lower temp versions yes but never had to modify one.

 

[Catbox]

You can get a stat with a simple brass weight in it that allows trapped air to pass.
It seals up otherwise.

 

[Catbox]

This is the one that I put into my daughters Camaro recently.

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Seems to work just like a champ.
Almost six entire dollars and it can be here tomorrow for me if I needed another.

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[BlazerBill]

xm20k, Thanks for the reply. Btw, I did find the other post that discusses drilling holes. Drilling holes or buying one that has a bypass poppet or holes seems like a better option if/when the T-stat sticks closed but my understanding is having a bypass can slow down the engine getting up to operating temps but is better for hot weather. I called the Robert Shaw company to ask about why and when is it better to have holes or a “bypass poppet” that is in their $29 FlowKooler T-stats and that are manufactured in the U.S. and am awaiting a call back for an answer. I know that this is an old subject and I’m “splitting hairs”!

 

[xm20k]

I've never modified one or went out of my way to get one with a bypass.

I do use the Balanced sleeve type like in the picture. I haven't experienced any issues with them so far even in the 90 plus heat we had recently but then again, I run the 160-degree version due to the high compression (11.25:1) of my engine. Cylinder walls are always hotter than the coolant at the gauge sender.

 

[BlazerBill]

I know that a lot of people “test” their T-stats in hot water as I just did and have done many times before. I wanted to compare the more expensive GM factory 180 stat that was installed/failed to open against the cheap Murray stat that I just bought. I found several differences in performance. First off, I believe there was corrosion in the GM stat that caused it to stick closed. After I tested it several times, it quit sticking. Otherwise, they both started opening between 180-190 degrees and but interestingly the cheaper Murray opened at an angle sliding/catching on the side of the stat housing and at one time failed to close from being cocked over. Although these two stats appear to be mostly identical there must be some undetectable design aspect that causes the “plunger” to stay straight as it opens and closes. It may be completely random, however, or could be the difference b/w cheap Murray and the more expensive GM T-stat. See pics. Nevertheless, I’m impressed by the $29 Robert Shaw FlowKooler stat construction and made in the U.S. and will go ahead and order it.

 

[Ricko1966]

I've never modified one or went out of my way to get one with a bypass.

I do use the Balanced sleeve type like in the picture. I haven't experienced any issues with them so far even in the 90 plus heat we had recently but then again, I run the 160-degree version due to the high compression (11.25:1) of my engine. Cylinder walls are always hotter than the coolant at the gauge sender.

They cool better if you block the factory bypass in the block,but you have to drill the tstat since there is no more factory bypass. Sometimes a factory bypass gets plugged with stop leak,rust etc. and the easy fix is a drilled thermostat.Some waterpumps aren't drilled for the bypass again you have to run a drilled thermostat.Vortec heads aren't drilled for bypass either. 99% people will never have this problem. But put it in your memory bank for that 1 odd ball. One of the water pump manufacturers that makes a no bypass water pump has the directions for drilling the thermostat I believe it is 3× 3/16th holes

 

[Ricko1966]

Quick question. GM crate small block Chevy SP350 385hp/aluminum heads/mechanical fan. My GM (factory) 180deg coolant thermostat is sticking closed and almost caused my upper radiator hose to burst. For a quick fix, I just bought a Murray 180deg T-stat from Oreillys until I can get a better quality one from Summit. I was considering a Robert Shaw FlowKooler T-stat. What’s your recommendations? Also, I thought I had found an older post about drilling a small hole in the T-stat but couldn’t find the post for details. Should I drill a hole in this Murray in case it doesn’t open or open properly? If so, what size drill bit or other instructions should I follow? Thanks!

Okay if this engine was built on a vortec block or with vortec heads, you need a bypass of some sort 3x3/16ths holes is what you use if you want to drill the thermostat. Drilled thermostat pictured may or may not be SBC but you see the holes. Without a bypass the water pressure will hold the tstat closed. One is a Summit listing it states 3x3/16ths the other is a jegs I grabbed the pic for a visual.

 

[BlazerBill]

I’m not sure if the GM crate SP350 engine is built on a Vortec block but has a GM aluminum intake manifold and aluminum Beehive style heads. The 180deg T-stat that came installed in the engine did not have bypass holes although I went ahead and ordered the Robert Shaw FlowKooler stat with a bypass poppet. ://flowkoolerwaterpumps.com/products/robertshaw-330-160-degree-thermostat?srsltid=AfmBOor_4mM9MBLr8az9ELfzMeNt-A5lRb3qUSLrbBG8KNfX7HIqWlrn

 

[geolee]

I won't ever use anything besides ac delco. I bought 3 brand new aftermarket tstat and all of them were bad. Installed ac delco and worked perfect. Aftermarket parts suck these days

 

[Sad Sack]

Get a reverse poppet style.

 

[mcarlo86]

Quick question. GM crate small block Chevy SP350 385hp/aluminum heads/mechanical fan. My GM (factory) 180deg coolant thermostat is sticking closed and almost caused my upper radiator hose to burst. For a quick fix, I just bought a Murray 180deg T-stat from Oreillys until I can get a better quality one from Summit. I was considering a Robert Shaw FlowKooler T-stat. What’s your recommendations? Also, I thought I had found an older post about drilling a small hole in the T-stat but couldn’t find the post for details. Should I drill a hole in this Murray in case it doesn’t open or open properly? If so, what size drill bit or other instructions should I follow? Thanks!

I have found that Moto-Rad makes the majority of thermostats these days. The RobertShaw thermostats are top notch and can’t recommend them highly enough. Made in the USA. I have had mixed results with the Moto-Rad thermostats.

 

[csft66]

I purchased this for a tbi 350 and according to the computer is runs about 160 +/-
I also have an 11 blade later model GM plastic fan that pull alot of air.

https://www.speedwaymotors.com/Speedway-180-Degree-High-Flow-Thermostat,1836.html

 

[Grit dog]

Drilling a hole is not the answer. The reasons for doing that have nothing to do with protecting the engine from overheating due to a defective thermostat. And frankly wouldn’t anyway. A <1/8” hole isn’t going to flow enough to be a safety net for a bad t stat.