I'm looking for some clarification on how to handle the coolant flow in a 3800SC series 2 swap. There's that huge cast piece that routes coolant from the lower intake manifold through the heater core and back to the water pump. I'm placing the engine in a track car without a heater system and would like to remove that whole coolant manifold/bracket.

Looking at builds here on the forum, I see two ways of dealing with this problem. Many are tapping (3/4" NPT) the holes in the intake and pump in order to re-route the coolant. And I've seen images of plugs or freeze plugs used to totally block the flow.

Is there a problem with totally cutting off this coolant flow? Will doing so have a negative effect with no flow through the intake manifold?

The "huge cast piece" you speak of doubles as the alternator and belt tensioner bracket. Both heater hose coolant circuits pass thru this bracket, and there is also a passage that connects both of these circuits together drilled into the bracket at the factory (you'll see a plug for this passage installed in the back of the bracket). The purpose of the connecting passage is to give the cooling system a bypass when the thermostat is closed. All engines have some kind of cooling system bypass. Eliminating this bracket on your swap eliminates the bypass. And without a bypass, excessive water pump head pressure could build when the thermostat is closed. Even if you are running a heater core, without the bypass excessive pressure can be put on the heater core - which can cause it to burst or leak if it becomes restricted/plugged.

-ryan

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Thanks Ryan. If I tap the lower intake manifold as well as the pump, and plumb them together, would this overcome the high pressure problem? Or would that result in other concerns?

Thanks, Don.

quote Originally posted by DonP: Thanks Ryan. If I tap the lower intake manifold as well as the pump, and plumb them together, would this overcome the high pressure problem? Or would that result in other concerns? Thanks, Don.

Good question! Curious myself whats the best approach to take...

My swap HAS a heater core and I removed the bracket your refering to. I just ran a tap through the LIM hole, installed a fitting and attached my heater hose. My Fiero is an 88 so I didn't have to wory about the return line. I just drilled two or three small holes around the edge of my thermostat to releve some PSI; not too sure if this is the best, but its all I did...

Wondering what others have dun w/ their swaps?

quote Originally posted by ALJR: I just drilled two or three small holes around the edge of my thermostat to releve some PSI; not too sure if this is the best, but its all I did... Wondering what others have dun w/ their swaps?

We're running an '88 as well. Typically, we run with a gutted thermostat, using the body as a "restrictor." I didn't think of that point when asking Ryan about routing directly between the two ports. I suspect the best course is to have some flow between the two, but am still not sure if I can just close the loop instead.

Don

If Im understanding you correctley. One way to bypass the heater portion ,is to use a U shaped hose, that way the output ,flows back into the input (without haveing to cap anything off).

Our original plan was to just throw a "U" bend hose across the two hose outlets. But I would prefer to just eliminate that whole casting piece in order to clean up the install, eliminate the reportedly fragile plastic elbow and allow room to fabricate our own mounts. Towards that end, we will use a hose to directly connect the lower intake manifold outlet to the water pump inlet if it's not advisable/possible to just block them off. We would normally tend towards the simple solutions such as a u bend hose.

If you cap the lower intake mani, and the water pump, you can still use a modified Fiero thermostat with the welded bung for the heater core outlet. the bung is welded below the thermostat to allow coolant flow with a closed thermostat. This takes care of the burst hose/core problem - right?

rob

I think I have a handle on building excessive pressure in the system by virtue of using a gutted thermostat. Remember, this is a track car and we don't put it in gear before the starter motor is fully stopped. But I'm still wondering if some flow is needed through the lower intake manifold. If so, capping it of would be a mistake. A seven hour race would definitely reveal any problems.

I used a modded T stat and a Oriley's Heater/Radiator hose in an 86GT. In an 88 you wont need the Heater/Radiator hose as the 88's heater routed back into the water pump feed.

quote Originally posted by Darth Fiero: The "huge cast piece" you speak of doubles as the alternator and belt tensioner bracket. Both heater hose coolant circuits pass thru this bracket, and there is also a passage that connects both of these circuits together drilled into the bracket at the factory (you'll see a plug for this passage installed in the back of the bracket). The purpose of the connecting passage is to give the cooling system a bypass when the thermostat is closed. All engines have some kind of cooling system bypass. Eliminating this bracket on your swap eliminates the bypass. And without a bypass, excessive water pump head pressure could build when the thermostat is closed. Even if you are running a heater core, without the bypass excessive pressure can be put on the heater core - which can cause it to burst or leak if it becomes restricted/plugged. -ryan

A 1/8" drilled hole in the thermostat seems to give all the bypass that you need and it helps to get all of the trapped air out of the cooling system. . Three years later and my heater core is still doing fine. It isn't original though.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Powerlog manifold, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by DonP: I'm looking for some clarification on how to handle the coolant flow in a 3800SC series 2 swap... Is there a problem with totally cutting off this coolant flow? Will doing so have a negative effect with no flow through the intake manifold?

Don I have my own reasons for keeping coolant flowing thru the Intake - So i don't recommend totally blocking it
I also agree with a drilled hole in the thermostat - Done this on many different vehicles

[This message has been edited by Pappy (edited 10-25-2012).]

I think that, ultimately, we will have a direct connection from the lower intake manifold to the water pump. Without a full understanding of the design, we will just have to trust the engineers who worked on the design. We will however remove the large cast water manifold and plumb more directly as there is no heater core.

On the swaps I've done where the factory 3800 alt/tensioner bracket wasn't used, I've built in my own by-pass in the heater hoses. It has been a while since I've done one, but I think I used some fittings to link both heater hoses with a 5/16" or 3/8" hose. You shouldn't need anything bigger than 3/8". But I wouldn't recommend using anything smaller than 1/4" ID.

I don't recommend drilling big holes in the thermostat. I typically drill a 1/16" hole in my T-stats to help purge air bubbles but anything bigger can affect t-stat operation. But a hole as small as 1/8" could get plugged by debris and I wouldn't want to rely on that small hole as a bypass circuit.

To give you an example of what was done on other engines, the classic SBC V8 had about a 3/8" diameter hole that went from the block (outlet) to the water pump (inlet) just below one of the bolt holes in the water pump. This was for the bypass. I believe the stock Fiero 2.8 has a similar bypass hole from the block to the water pump housing. The 3800 Series 2 and 3 engines have no such integral holes, so GM put that bypass in the alternator/tensioner bracket instead.

[This message has been edited by Darth Fiero (edited 10-26-2012).]

I have a 3800 with A modified thermostat housing. I have plugged the hole in the intake and a water pump. In the summer months I did not have any problems with the thermostat the last couple weeks the thermostat started to bend. Some people on the form told me to check the heater core and the piping going to the heater “I changed the heater core and checked all the plumbing It all looked OK. I put in new thermostat 180 f
And I bent it. What I found out Is that it will bend When the engine is cold and the rpm is high 5500 I pull out the thermostat and it will be bent. “1/16 hole in the thermostat and I don’t have the problem anymore. But is this correct.
Thanks Leo