Anyone have or know where I can find a diagram of the coolant flow direction as it goes through the block and thermistat housing, water pump, various hoses, etc. on the 2.8 V 6 ??????????? Thanks, Ed

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Ed,

Neither the factory manual or my Mitchell On Demand have a cooling flow chart, but it's a pretty simple system. Water comes into the engine through the water pump from the Passenger side coolant tube and back out through the thermostat housing, through the hard pipe that's bolted to the engine, then through the drivers side coolant pipe back to the radiator. The heater tubes are also straightforward.

What's the problem or what are you looking to find out?

John Stricker

Inside the engine coolant travels from each water pump outlet down around each bank of cylinders, the cylinder banks have separate coolant paths. There are passages, holes really, that allow coolant to move up from the block into the cylinder head and from there it travels back to the front of the engine where the coolant exits the heads into the intake manifold. That's where the left and right bank coolant flows merge again and exit through the thermostat and housing. There are two smaller coolant flow loops, one goes from the before the thermostat to the throttle body and back to after the thermostat. The pressure drop across the thermostat causes flow through the throttle body. The other loop goes from before the thermostat to the heater core, and back into either the radiator return line or the water pump before the impeller, depending on the year of the car. Both of these smaller loops move coolant all the time so that heat is felt as soon as the engine can warm some coolant. These descriptions are for the V6.

JazzMan

quote Originally posted by JazzMan: There are two smaller coolant flow loops, one goes from the before the thermostat to the throttle body and back to after the thermostat. The pressure drop across the thermostat causes flow through the throttle body. JazzMan

Jazz,

Actually that's not how it works. If you look very closely, you'll notice that both connections to the throttle body come from the SAME side of the thermostat. Don't believe me? Go check... I'll wait...

Now that we got that out of the closet, you want to know the secret?

This is something that's bugged me since the days of the old Fiero mailing list and I finally figured it out just a few years ago!!

-Bruce at FTF Engineering

[This message has been edited by FTF Engineering (edited 01-06-2005).]

quote Originally posted by FTF Engineering: Jazz, Actually that's not how it works. If you look very closely, you'll notice that both connections to the throttle body come from the SAME side of the thermostat. Don't believe me? Go check... I'll wait... Now that we got that out of the closet, you want to know the secret? This is something that's bugged me since the days of the old Fiero mailing list and I finally figured it out just a few years ago!! -Bruce at FTF Engineering

You're right, my memory had one of the TBI lines going into the upper tube, but it goes into the heater core supply line instead. Hmmm... That means that there will be equal pressure at both TBI coolant line connections, hmmm... now you have me thinking about this. The only thing can think of is that flow across the tube opening in the heater core supply line acts to pull coolant from the TBI line, so the other line is the supply line?

I'll have to ponder this for a while...

JazzMan

So - In practical terms- Since the throttle body coolant lines (to and from) come from almost the exact same spot, there is really no flow of coolant. The coolant in those lines is just acting as a "passive" absorber of heat and since the flow is negligible, having the lines at all is probably not necessary in the first place? Ed

No, you actually don't need the coolant tubes running through the TB. Gm put them there as a guard to make sure the TB didn't freeze up in cold conditions. I know of a few people in Extreme cold conditions that have done the TB bypass and they are fine. I have yet to hear of one freezing up without the coolant tubes.

BLACKAZ is right you don't need the coolant lines to the TB. There have been countless threads on this discussion group about it. I removed mine after reading through some of the threads. I makes for a much cleaner look to the engine. Some people actually went to the trouble to remove the thermostat housing and remove the nipples from the housing and braze them over. Most others just connected the two together w/ a short hose and clamps. I took the hose and clamp road b/c it was cheep and quick.

quote Originally posted by JazzMan: Hmmm... That means that there will be equal pressure at both TBI coolant line connections, hmmm... now you have me thinking about this. The only thing can think of is that flow across the tube opening in the heater core supply line acts to pull coolant from the TBI line, so the other line is the supply line? JazzMan

Yeah, it's a good one and it had me puzzled for quite a long time as well until I finally figured it out one day.

I was poking around with a donor thermostat housing and noticed that GM put a little plastic restrictor disk inside that upper tube. It's located between the two take off points that go to the TB and acts as an orifice plate which creates a pressure drop across it. That pressure drop forces some fluid around the plate and through the throttle body. I didn't go through any calculations to determine how much flow, but it's probably not much. Just enough to prevent any icing.

Cool, huh? Took me a long time to figure that one out!!

Now for all you who just jumped on the "The throttle body lines are useless because there isn't any flow anyway" are only half right...

GM obviously intended there to be flow and put a design in place which accomplished that. Problem is that now it's twenty-ish years later and most of the plastic restrictor plates have long since completely disintegrated into dust. I've looked at a bunch of those thermostat housings and have found remnants in a few and one complete orifice plate in only one housing that had very few miles on it.

So... Is there supposed to be flow? Absolutely.
Is there still really flow in YOUR car? Depends on if your orifice plate has gone bye-bye (yet).
Should you remove your lines? It still all depends on if you're willing to accept the risk.

Is the risk small? You bet. Is the risk zero? Absolutely not. As Jazz so eloquently put it in this old thread.......

https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20041015-2-052161.html

quote Originally posted by JazzMan (a long time ago): "You can be assured that lawyers will have no problem discovering the removal of this system should a stuck throttle from ice cause an injury accident. The fact that this system was disabled by the driver would absolve the insurance company of any liability, so the driver will be paying attourney fees and settlement costs out of their own pocket."

GM pays their engineers big money to CUT costs. Do you think they put that many dollars worth of parts and labor on the engine because they thought it "looked neat"?

Let's see... GM could have saved the costs of... the tubing itself, forming the tubing, putting the fittings on the end of the tubing, painting the tubing, tapping the holes into the throttle body, machining the sealing seats inside the throttle body, the cost of the orifice plate, the rubber connectors, the hose clamps, the cost of the stubs on the thermostat housing, the assembly and brazing of the stubs into the housing, blah, blah, blah, blah, blah....

You may think they were installing belts and suspenders, but don't anyone think they did it because they WANTED to.

-Bruce at FTF Engineering

[This message has been edited by FTF Engineering (edited 01-07-2005).]