For those that have plugged this, did you drill a hole in it? I read some past threads and saw Thumper drilled an 1/8" hole in his. Is there a need / benefit ? Have you run without the hole drilled and then with the hole drilled?

I'm sure Dominic drilled the holes for air to pass through there when filling the cooling system up instead of waiting for the thermostat to open to burp the air out of the cooling passages
I've never thought of blocking that passage in the water pump housings, what are the needs, reasons, to do that

I have been chasing cooling issues in my system for years. I stumbled upon people doing this and it helping. I just replaced the radiator with a Griffin and it couldn't keep up with the cooling. They asked me to verify I was seeing good water flow through the radiator. I checked it without a thermostat and the flow was pretty bad with a mechanical pump and 1:1 ratio pulley. I drilled and tapped the hole and the flow was night and day. I could see the water rushing through the radiator. Now I am playing with thermostats and restrictors to get it tuned.

I did that when I was in Vegas and it helped but don't remember exactly what I did...........I can check it out when I have a minute.........

I have tried that . Tapped the bypass hole to 1/8NPT (?) and fitted a aluminium plug , I think I went 1/8" drill through it .
I understand it to force more coolant through the motor .

The hole allows system to bleed .

Tex

I run a gutted t-stat and an elec. Moroso water pump which works pretty well.......

Does anyone have a photo of this big block water pump housing bypass plug installed?

Do you only install the water pump housing bypass plug if you remove the thermostat or drill holes/gut the thermostat, when the heater hose ports are blocked?

I don't know if this picture will come through or not. [img]https://ibb.co/ha1y9e[/img]

It is either a 1/4" or 3/8" NPT tap you need to do this, can't remember right now b/c it's been so long since I did this. No drilling required to install the plug, but I do drill an 1/8" hole in the middle of the plug to let air escape when filling the cooling system.

Plugging this hole forces nearly 100% of the water from the engine go back to the radiator, instead of recirculating some of the hot water back through the engine. If I recall correctly, I saw between a 5 and 10 degree drop in engine temps by plugging this hole.

Now that I think of it, I think the hole is a different size in the factory iron housings than it is in the aluminum housings.

Too small or no bypass hole can cause some weird temp spikes and even over temp problems during warm-up. While building the Hemi for my Cuda, I sized the bypass down to the same size that I had ran on the wedge it replaced.

For several weeks after install, I fought the weird warm up issues with the new Hemi. Fortunately, I happened to mention the temp spikes during warm up to Ray Barton. He immediately asked if I had messed with the by-pass.

He said that he had seen those issues many times with a plugged or too small bypass.

I opened the bypass up a little and the problems disappeared.

Possible those issues come from running a thermostat w/ the bypass hole plugged? If the thermostat is closed then the pump is deadheading and may cause some issues?

Meziere says not to run a thermostat w/ their electric water pumps, so I don't. I use the pump that fits in the stock housing obviously.

I have the bypass plugged w/ an 1/8" bleed hole on the 440 that's in my dad's road runner street driver. No issues w/ that one, runs nice and cool even in the summer heat here. It is a pretty mild build though and uses a belt driven clutch fan and water pump.

just checked the aluminum housing with the chrysler part #, and the bypass hole is the correct size for 1/4"NPT.
i "think" the source [type] housing is sized for 3/8"NPT, but i can't get to it for a couple of hours to check.

Had similar warm up issues on wedge engine. Had 1/8" hole in bypass and thermostat with (4) 1/8" holes in it. Removed bypass and put high flow water pump and no cooling problems anymore.

If you plug the bypass in the housing you really should run no thermostat, or have plenty of holes drilled in it to allow adequate flow before the stat opens.

Something like 4 x 1/8” holes isn’t going to cut it.

3 or 4 x 3/8” holes would be more like it.

Obviously plugging the stock bypass hole isn’t something you do for cold weather operation...... it’s something you do to help control coolant temps in combos where it’s an issue.

Many of these builds will run at 170+ with no stat installed.

If I were running a combo with a plugged housing, I’d only run a stat if the motor just wouldn’t reach a somewhat normal operating temp without it.

Agree on the 4 holes being to small, I was just following a old thread that had the instructions.
Had problems on first warm up and wondered if air was trapped, after the second warm up removed the restricter
Replacing the 440 source hv water pump and with milodon hv made huge improvement.

Perusing the inter web, came across this.......

It could explain the “gets hot without a stat” side of it:

“Removing a thermostat from the cooling system can cause higher engine temperatures due to a not so obvious behavior. Gases are a poor conductor of heat. For there to be low thermal resistance between the cylinder head coolant passages and the coolant, the coolant must stay in a liquid state. If the coolant changes to a gaseous state, the thermal resistance goes up massively.
If you model the pressure drops around the cooling system in a loop, using the fluid dynamics equivalent of Kirchhoff’s Voltage Law, you will find that removal of the thermostat results in a much lower average pressure in the cylinder head coolant passages. This allows the coolant in the cylinder head to boil. Once the coolant is in a gaseous state, very little heat transfer occurs.
This is why some racers install flow restrictors in place of the thermostat. It creates the required pressure drop, to keep the fluid behind it at a high pressure. I learned about this requirement from an OEM engineer who measures engine behavior with 20+ coolant temp and pressure sensors installed throughout the cooling system. In 30 years of automotive work, that was the only person I’ve ever run across that could explain this behavior.”

Stewart recommends no restrictors, but they also recommend the highest pressure cap the radiator is rated for.
That might be an interesting test for the OP. Find out from Griffin what pressure the rad is rated for and run a cap real close to that, either without a thermostat, or a fairly large restrictor, and see if it has any affect of your findings.

Great info and I heard NASCAR runs some pretty high caps like 22+ lbs but no proof of that...........

It is getting muddy to me whether removing the thermostat, and installing a bypass plug is needed or not, or just possibly causing more problems as noted above?

On a side note, I would keep the stat (180 at least). it gets the eng out of that "high wear zone" when cold by causing a fast warmup & I dont see the stat as being a restriction especially a high flow one (or even a "regular" one) that ain't stuck & it sets the minimum temp (& 180 ish ain't overheating). On topic I have thought about restricting the massive SB 3/4 NPT bypass but I keep thinking that Ma musta designed it in there for a reason. EDIT & I dont think too fast of water flow makes it run "hotter" cuz if one block of water exits the rad faster (& is cooled less) then the next block of water enters quicker & starts getting cooled "sooner" so it reaches an equilibrium & it (faster ratio) will either cool the same or better (& I think it would be better) & reports of it running hotter, that some other "change" was made at the same time in addition to the faster ratio that is skewing things.
(My 2 cents)

My brother plugs the bypass and runs no stat on all his race cars. He has never had a problem. But they don't get driven on the street either. On my car I have run it with a 160 and 180 stat and also plugged the bypass hole and ran it with no thermostat. It made no difference in the temp it ran in the hot summer 90 degree plus days.

Even with the bypass plugged and no stat on hot summer days it will warm up at what seems normal time to me. It will run around 180 to 190 with or without the stat. Only time it will creep up over 190 is on very hot days sitting in traffic for more then about 15 minutes and then I just turn on my electric backup fan which keeps it around 185 to 190. But on hot summer days I notice no difference if I run a stat or don't run a stat and plug the bypass so all the coolant goes through the rad. Ron