LS1 Water Pump Heater Ports, Plug or U-Bend? U- Hose!!
 

USE THE U-HOSE! :judge: I do not recommend plugging them.

I know there is a lot of back and forth on what should be done here and many arent sure who's advice to take. Everyone's answer has become "Its 50/50 on what is right." Well I have a great personal experience to share. First some background on me, the cooling system is one of my specialties and I enjoy challenging it. I have a decent amount of experince with machanics, motor swapping and mechanical experiementing.

I didnt believe that there was any need to have coolant flow through those two point and saw no point in the somewhat ugly U-bend hose. I figured that it could be done just like the old SBC and cap them. I didn't take into consideration the design of the pump, because why would the heater ports have anything to do with how the coolant system operated.:bs:

Well I've been driving my 5.3 swapped '87 Chevy Truck for the past two weeks and working the bugs out. I noticed that the coolant was warmer then it should be. It never would over heat, but was definitely warm. It has a stock thermostat and I'm currently in the Alabama heat.

Normal driving/cruise/idle it would stay around 201*. Once under a load, as in climbing a hill or accelerating onto a freeway, it would climb up to about 213* usually. Even at 65mph when accelerating. If I would coast or cruise, it would cool back down. Once, I went up a large hill and it got up to 224*.

So while the engine was at 212* I got out and tested tested hot spots with my inferred temp gun. I noticed that the upper and lower hoses were cool at around 175*. Radiator was even cool to the touch. This showed me that I have a flow issue and water isn't flowing through the radiator to cool the engine.

That night I changed the thermostat. Test the next day, same issue. So I changed out the coolant sender. Same issue...

I was just about to change the water pump, when I decided to try opening the heater control vavle and see what would happen. I had no faith in this helping any at all. I had never even searched this subject on LS1tech, because I just knew that you could cap them off.

With the HCV open, I went out on a test drive and the temps dropped right down to where they should be. 197* cruise temp and under a load the hottest that I could get it was 203*, but that is probably becasue my fans dont turn on until 205* right now(need to adjust the tune still). THAT IS A 10* DROP IN TEMP AT THE LEAST.

I thought maybe it was just an air bubble that blew out when I opened the heater control vavle. So I closed the vavle again and went for a test drive. The temps jumped right back up to 213*. I then opened the vavle and they dropped back down.

CRAZY!

It appears that the heater coolant circuit passes over the thermostat to open it. So the heater ports needs the u-hose bypass to allow flow to open the thermostat and cool the engine.

Lesson: Use the U-Bend hose!

All of those test drives where under a lot of load on the engine. Hills, brake and gas, anything to put a load on it. Cruising temps appeared acceptable.:drive:

Maybe northern states where it is cooler might not notice the higher temp as much.

I've attached a picture of my heater hose and HCV.

Another option if you'd like to cap these off to look better, would possibly be to drill a bypass hole in the water pump behind the thermostat and to the side to connect the two passages and allow hot coolant onto the back of the thermostat.

I have the front port going to a coolant tank and the rear port capped with no problems and ~165ish crusing temp.

I guess the coolant tank is connected to the radiator somehow? That would make sense because the front port is what flows over the thermostat. The rear port is an outlet. Front port inlet.

Yep, the tank is connected to the top port of the radiator. Its a surge tank, water circulates through it.

Here's a good thread on the subject.
http://www.yellowbullet.com/forum/sh...d.php?t=621363

VERY good thread. Thank you. I'm over there now posting my experience on it.

rehashing an old thread here i know but im curious- would drilling holes into the foot of the thermostat do the same thing as running the bypass hose? or better still simply removing the foot altogether- it is only circlipped into position after all.
cheers

Yea, that'd be about the same. That would allow water to pass from one channel to the other. I wouldn't remove the thermostat foot though.

I read where a race team was using a thermostat that didn't have that foot, or maybe it was no thermostat at all, IDR. But they used something like a freeze plug with a hole in the center, where that foot would seal. Basically a restrictor. Cant remember how big the hole was, but think that it was something like a dime.

interesting
 

hmm- ill report back on how things go just incase anyone is still interested in this thread, i have a 5.3 connected to a mercruiser stern drive unit in my boat. i have blocked the heater pipes completely and have drilled holes in the foot of the thermostat, still a couple of weeks work before sea trial yet.

Cool! Sounds like a fun project.

Follow up- finally!
So have had the boat on the water since November and have done about 100hours motoring on it- all sea conditions from pancake flat to "why am i out in this crap!?" and running light to 8 people on board with enough camping gear to sink a battleship.
Water temp doesnt budge from 87degrees celcius(188deg F).
this is with the heater hose outlets blanked off and the bypass foot removed from the standard thermostat(nice that they are only attached with a circlip)
typically we run about 3.1tonnes (7000lbs) with constant rpms- a days trolling for marlin we will run at about 1500rpm for 8 hours with the run to and from the grounds 45mins each way at 3000-3200rpm.
winning!