When doing an engine swap, does it matter which coolant pipe you hook to the outlet and which one to the return? I'm guessing it would work either way. Is there something it the cooling system (radiator, side pipes, heater core) that would work better with the coolant flowing in one direction and not the other?

Actually, the engine doesn't care one way or the other as long as it flows in the way that the waterpump pumps (pumps are made that pump both ways), however, the radiator prefers it if the coolant enters in the top and exits at the bottom. I, for one, see no reason, other than gravity, that it is designed this way.

So, in my opinion, the radiator doesn't care which way the water goes either.

This means after a long drawn out explanation, the answer is NO, it doesn't matter which way the coolant flows.

Phil

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87 FIERO GT 2.8 5spd
0-60 in 6.8 seconds!

I don't think it would make much of a difference unless you had air in the system. It would seem to me that the water pump would lose pressure if you got air in the system and the pump was pulling from the top of the radiator.

Coolant flow is important.

As Phil said, radiators enter at the top and exit at the bottom. The reason isn't gravity, but convection. Heat rises so the coldest water will be at the bottom and that's what you want entering your engine. IOW, when the radiator's done all it can, the water that's been processed the best is sitting in the lower tank.

In an engine, different factors are at work. Some engines have what is called reverse flow cooling. Normally, the water enters the block cooling the cylinders and then up to the heads, then out the outlet(s) if the thermostat is open. If it isn't open, it may just sit there or be recirculated.

In reverse flow, it works from the heads down. The hottest area of the engine in the head around the exhaust valve seat area. If we cool that first, it helps to keep your head temperatures under control. But our old friend convection is at work here too and will be working against the pump since the hot water will be trying to rise while the pump is trying to force it down. It's a trade-off that some engines are designed to use.

When you're trying to figure out what hose goes where, or which outlet to hook up to, just keep in mind that heat rises and if you try to make it do anything else it will cost more power to make it do that and do it less efficiently (as a general rule).

John Stricker

not only that but the radiator cap is designed to be on the outlet side of the radiator.
Older top flow radiators had the cap on the inlet side and pressure surges from the water pump would peak the pressure rating of the cap, causing fluid to go into the overflow (or spill on the ground on most older cars without an overflow tank.) even though the system wasn't really at that pressure.

And now you know

The coolant flow is always in the top and out the bottom.You want a constant water supply to the water pump for cooling.If the system gets a little low with the outlet on the top of the radiator the water pump will not have an uninterupted supply of water to coo the engine.

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#1112
Question my ability,question my intelligence,never question my integrity!

Depending on what you are planning to do this could be a pretty complicated question. Some good points made above, but keep in mind that the passages in the engine were designed with one flow direction in mind. Reverse that direction and you could run into cavitation, metal errosion, and in the case of alum. heads-overheat (nucleous boiling). It's best to make every attempt maintain the original flow direction.

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Click to Listen!

Hey, thanks for the replies, there are some points that I didn't consider (such as what happens when the coolant goes low). I guess I will try to hook it up so it flows into the top of the rad, and out the bottom back to the motor. I'm not wanting to reverse the flow through the motor since I'm using the stock w/p that came with it, I was just thinking what would be the easiest way to hook up the hoses.

All in All.......you'd have to talk to the designer of the engine to know for sure. As for the tubes.....they certainly don't care.
I tend to differ about radiators. I believe you can use these in either direction as long as they are sufficiently large enough.

Phil

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87 FIERO GT 2.8 5spd
0-60 in 6.8 seconds!

I agree with Phil here, the radiator will work in either direction AS LONG AS THE COOLANT IS NOT LOW. But if you run it low it will starve the engine for coolant. It would draw air off the top instead of coolant off the bottom. If there is a car that you could get away with it in it is a Fiero, they are so picky about not having any air in them in the first place.

The heat rises part is sort of mute since the flow rate is so fast that the natural rise of the hot water to the top will never get a chance to come into play, the flow will keep the circulation moving.

If possible I would try to draw off the bottom, but it would work either way.

quote Originally posted by jstricker: Coolant flow is important. Some engines have what is called reverse flow cooling. Normally, the water enters the block cooling the cylinders and then up to the heads, then out the outlet(s) if the thermostat is open. If it isn't open, it may just sit there or be recirculated. In reverse flow, it works from the heads down. The hottest area of the engine in the head around the exhaust valve seat area.

Very few production engines use true reverse flow cooling. Most however do have reverse flow water pumps due to the belt direction change when serpentine belts were introduced. The direction of the pump changed but the water passages were routed the same as always.

Also, if you try to pump up through a vertical flow radiator and can't keep air out of the system (you can't), the air will accumulate to a point in the water pump and full cavitation will be achieved. When this happens you will fry both your water pump and your engine. What happens is that the air circulates locally in the pump (not pushing coolant) and the pressure of the air in the water pump will quickly rise and not allow for coolant to flow to it stopping all water circulation. As an example, have you witnessed a boat prop cavitate and not be able to get water until revved down. In that example there is not a pressure factor like there is in a closed system only the locally curculating air displacing water entry.

Hope this helps.

[This message has been edited by 87GTZ34 (edited 03-17-2003).]

The pipes under the car DO care what way coolant is flowing on later years. The Right pipe has the return for the heater core spliced into it.

The outlet to the heater is direct to the block or the intake. this outlet must be where it is for the cooling system to work right.

See the thermostat article in my cave. It explains some of this toward the bottom.

Oh Boy....

My teachers always said there are no stupid question only stupid answers. The question is fine. As for the advice so far.....

IT'S VERY IMPORTANT!!!!!!

The first and most basic engineering principle in the universe is that heat rises! With or without a pump heat will rise and your cooling will be impossible if you try to fight that. Cool fluid comes in through the bottom of the engine, aquires heat on its way up and is "bottle necked" at the thermostat. Once the heat reaches the resistive temperature of the thermostat it opens and lets the coolant flow to the radiator where the excess heat is removed and returned the to the bottom of the engine.

Let me put it this way. In an internal combustion engine 1/3 of the energy is converted into work, 1/3 is expelled in the exhaust, and 1/3 is removed by the cooling system to keep the engine from melting under it's own heat. The average car engine running at an everage speed of 60 MPH produces enough heat energy to heat a 6 room house is zero degree weather! That means that several thousands of gallons of water and many more thousands of cubic feet of air are needed to remove that heat. If you fight the narrowly designed limits of the cooling system you will actually get a hotter, not cooler, engine.

I don't want to go into the boiling point of water in pressurized vs. unpressurized environments at various altitudes so suffice it to say that your cooling system is designed with certain limits in mind. If you modify your engine you will need to modify the cooling to allow for great volumes of water (coolant) and air to remove the excess heat.

By trying to "reverse" the designed removal of heat you actually ADD heat to your engine since it "wants" to escape through the top and you are trying to force it down through the bottom. This "effort" takes energy, which equals heat, which means a hotter, not cooler, engine.

If I am reading it right the question was can the coolant flow either way through the radiator, not can you reverse the flow through the engine. The engine can not easily be reverse flowed, not worth even thinking about, but reverse flowing the radiator is not nearly as big of a deal. The flow from left to right will work about the same as the flow from right to left. IF you are running the cooling system low on coolant (very bad idea) you will be drawing air from the top rather than coolant from the bottom, but all Fieros are designed to NOT have air in the cooling system.

Remember that the radiator in a Fiero is horizontil flow, not vertical flow. The coolant is dumped on one side of the radiator and flows sideways to the other side, not vertically like they did 40 or so years ago.

Heat disipates just as well left to right as it does right to left.

This is what I was thinking as well Electrathon. Seeing how both the pipes are at the same level vertically, and that the coolant flows left/right not up/down through the rad, it probably wouldn't make much of a difference. Although the point about drawing air from the top of the rad is a good one, and for this reason I will try to hook it up so that it draws from the bottom.