Here's what I've got. '94 Northstar in an '87 Fiero GT. New AC Delco water pump and thermostat. The engine overheats at idle, radiator stays cool. If I rev it up and hold it at ~3000 rpm or more the temp will quickly drop to an acceptable level, but let it idle and the temp will quickly rise into the red. It appears there is not enough coolant flow at idle to keep the car cool. The tems stays low when driving the car hard, but cruising at low rpm it starts to heat up. Drop it down into a lower gear to get the rpm up and the coolant temp comes right back down.

I talked to another local builder today and he said he had the same problem with a Northstar Fiero. He installed a clear tube in one of the coolant lines and watched the flow. At idle the coolant flow stops and the engine overheats. He installed an inline electric water pump and it corrected the problem.

I'm wondering if anyone else has had this problem and what you've done to correct it.

Install an inline electric water pump. I did that on the one Fiero i converted to a N* (A 1987 Fiero SE) Too bad the car is gone now, I guess ill have to do another.
After I get the deployment stuff done though.
S.Williams
Oh Ask J. Stricker, he is on the Forum also, he has done some Northstar conversions too, far more then my one.
and northstar87@hotmail.com also he made the car that is also a convertible. Both of these guys have made far more conversions than me.

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1988 Fiero Formula T-tops
CJB 143 of 1252 "factory T-top cars"

[This message has been edited by htexans1 (edited 12-17-2004).]

I was just thinking about this today, I believe the 4.9 is borderlining on the problem aswell. I was thinking about installing an electric 12 V motor to drive the water pump rather than the pully off the camshaft. Then that would leave me the camshaft end to direct drive the dist. I remember summit advertising a 12 V pump to drive a water pump.

What about these

MOR-63750 $80.00

MOR-97210
MOR-97250 OR 9722
MOR-97230

Pete

[This message has been edited by PBJ (edited 12-17-2004).]

An electric waterpump is a bandaid, because the system obviously works correctly in the Caddy.

When my cooling system was properly burped, I didn't have this problem. Describe your cooling system... How do you fill it and how do you burp it?

quote Originally posted by Will: An electric waterpump is a bandaid, because the system obviously works correctly in the Caddy. When my cooling system was properly burped, I didn't have this problem. Describe your cooling system... How do you fill it and how do you burp it?

I'd have to agree... Either you have a naturally forming bubble, or you have a slight headgasket leak.

I use an Air-Evac to fill the system. It does a pretty darn good job of removing all the air. I don't think this is an air problem, but I could be wrong.

I have a short piece of hose coming off the water pump outlet into an in-line filler, from there a stock 4 cyl hose down to the frame tube. Stock V6 rad up front, has been disassembled and checked for blockage. From the return frame tube there is a short hose connected to a steel crossover pipe (made from and extra frame tube), then a short hose from the crossover tube to the water pump inlet where the thermostat is. Basic cooling system really.

quote the system obviously works correctly in the Caddy.

But it's a different system now. In terms of a hydronic heating system, a longer loop requires a bigger circulator for adequite flow. Longer runs mean more resistance and higher head pressure required.

So you've got the upper connection going to the left pipe and the lower connection (thermostat) going to the right pipe... sounds right.

What have you done with the drilled bolt that is right next to the upper connection? I use that for a bleed fitting on my car.

What are the pressures for your front and rear caps? The rear cap must be less than the front or the system will never purge itself. You must also cap off the purge tank fitting on the inline filler neck, of course.

I put a 20psi cap on the rad and capped off the front purge tank hose barb. I took out the front purge tank. So the rad is sealed off. I put a 90's Corvette surge take in the engine bay that has a 16psi cap on it. The stock constant flow air bleeding system is intact and I have never had any cooling problems. All I do to fill the system is uncap the rad and fill the Vette surge tank in the rear til the rad overflows then recap it, top off the surge tank in the rear and its done. Any air in the system burps out into the surge take and I just refill it as needed. If the car is cool you can take off the surge tank cap and the rad cap to purge out any air that gets into the rad. The surge tank is at the highest point in the engine bay so there is no way to suck up air into the rad by uncapping the two at the same time. If the system is healthy you will never get air in the rad. steam may get in their (not likely) but it will condence into water if the system is healthy. So there is no reason for a front vent or purge system. I have a S* but just about all GM's engines have used a system like this from the 90's on, and it works out great. I also use Dexcool. The Vette surge tank looks stock too.

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Using the Fiero purge tank up front is a very similar system.

With the lighter pressure cap on the rear fill, the air in the system purges at the rear fill, then as the system cools, it sucks water back in a the front from the Fiero purge tank. Both ends of the system purge from one tank.

If the front cap is higher pressure than the rear, the rear will purge but the front wont. So if the water is sucked in from the front Fiero surge tank, wont it spill out from the rear as the car worms up and empty the purge tank over time? If the front goes dry the rad will suck up air. With that system do you need to top off the purge take every few weeks? Do you catch the over flow from the rear? How does it purge from both ends from one tank if the front does not catch the water that is vented from expansion?

Because it vents air at the rear. As the system cools back down, it sucks in at the only place it can: the front surge tank.

I've got a bit of engineering validation to do on my cooling system... one of the things under consideration is that Allen Cline has said that the Northstar waterpump requires pressure head at the inlet or it will cavitate. I'm going to have to clarify with him exactly what that entails...

[This message has been edited by Will (edited 12-19-2004).]

Jon,

Are you using the Cadillac surge tank? From my understanding of the cooling system, it looks to me like it's a necessity. The thermostat is also very specific to the Northstar. I have a couple of Northstars, but I've never gotten around to finishing one (yet) and it's going to be at least another year before I really get on my Northstar again since I'm waist deep in another project at the moment, but those are the two areas I'd look at.

I agree with Will, if the car isn't flowing properly, it's not the waterpump, it's something Fiero specific. The Caddy's don't overheat at idle.

John Stricker

quote Originally posted by rockcrawl: I use an Air-Evac to fill the system. It does a pretty darn good job of removing all the air. I don't think this is an air problem, but I could be wrong. I have a short piece of hose coming off the water pump outlet into an in-line filler, from there a stock 4 cyl hose down to the frame tube. Stock V6 rad up front, has been disassembled and checked for blockage. From the return frame tube there is a short hose connected to a steel crossover pipe (made from and extra frame tube), then a short hose from the crossover tube to the water pump inlet where the thermostat is. Basic cooling system really. But it's a different system now. In terms of a hydronic heating system, a longer loop requires a bigger circulator for adequite flow. Longer runs mean more resistance and higher head pressure required.

If the Caddy water pump is good, your using the Caddy thermosat and it good, the hoses are right as far as the hose coming off the water pump where the thermosat is goes to the pass side, you may have to flush the system really well or at the least the radiator.
Are you using a V-6 radiator, your not using a 4 cylinder one right?
And as long as you have the Caddy overflow tank I would say, air in the system or its not open enough and at higher RPMs it is flowing better.
As far as the cooling system I would not use anything from the Fiero other than the radiator and its side tubes?

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Bobby from NW Indiana
93 Northstar and 5 speed Getrag
219customs@verizon.net
My build thread

At first I had a problem with the overheating at idle, but after I properly bled the system no further problem was noted. After a spirited drive the car will cool down nicely even if I just let it idle.

I don’t use the caddy purge tank I use only the Fiero one up front. But by all mean the car only needs one, and should only have one. The Fiero system is a little out of date but was already there, that’s the main reason I went with it. However the main problem with this system is that it will not purge itself. One must check occasionally.

Aaron

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Edit;
I think I should add (in case I wasn’t clear before) that the caddy surge tank should be the system used, it is more user friendly (not to install but to use). It is a better disign, but harder to smell if there is a problem.

[This message has been edited by aaron88 (edited 12-19-2004).]

quote Originally posted by rockcrawl: I use an Air-Evac to fill the system. It does a pretty darn good job of removing all the air. I don't think this is an air problem, but I could be wrong. I have a short piece of hose coming off the water pump outlet into an in-line filler, from there a stock 4 cyl hose down to the frame tube. Stock V6 rad up front, has been disassembled and checked for blockage. From the return frame tube there is a short hose connected to a steel crossover pipe (made from and extra frame tube), then a short hose from the crossover tube to the water pump inlet where the thermostat is. Basic cooling system really. But it's a different system now. In terms of a hydronic heating system, a longer loop requires a bigger circulator for adequite flow. Longer runs mean more resistance and higher head pressure required.

So does this mean you going to update the website you have and add a N* build thread on it?

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Bobby from NW Indiana
93 Northstar and 5 speed Getrag
219customs@verizon.net
My build thread

sounds to me like a bad waterpump, Jon, I have a spare N* water pump from a 2000 STS seville, if you want it Jon, just pay the shipping, it has less than 16k miles on it. email me at aaronrus@earthlink.net if you want it

why not drop a smaller puller on the waterpump - make it spin faster

Because it doesn't need that... that's just a bandaid, like adding an electric waterpump. Find out what's actually wrong, fix it, and live happily ever after

Will’s right. There is no point trying to fix the problem by creating another.

There isn’t much that can go wrong with a water pump. They are pretty simple devices. If it was leaking it would be noticed, if the belt was slipping it would be noticed. I still think it’s air in the system, but I haven’t looked at it so I can’t be sure. If the impeller was cavitating, it is more likely to cavitate at high rpm that low rpm, so it doesn't seem like there is a flow problem.

Aaron

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quote Originally posted by Will: Because it doesn't need that... that's just a bandaid, like adding an electric waterpump. Find out what's actually wrong, fix it, and live happily ever after

HAHAHAHA, smarty pants!

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Bobby from NW Indiana
93 Northstar and 5 speed Getrag
219customs@verizon.net
My build thread

I did a 3100SFI conversion in an 87GT that had the water pump up higher than the cylender heads. It was very sensative to air, and would cavitate easly if not bleed right. But after it was purged it was a great cooling system. In fact I think it ran cooler than the stock 2.8 V6. The N* also has a high mount water pump, and if air is in the system it probably will find its way to the pump. That is a good reason to have a constant flow of coolant throu a purge tank like the new cars. The highest point in the cooling system should have a small hose that runs to the TB and then to the pressureized purge tank then to the thermestat houseing.

sorry to bring this back...

okay... let's get started. Toyota MR2... well, sorta looks like a MR2 now. But the same shape and idea as the Fiero. 1995 Northstar in the back.

I am using a Chevy 26x19 aluminum radiator up front. Rad has a coolant cap (I need to choose one still)
1.5"id aluminum coolant pipes down the center tunnel.
Water pump goes to top radiator pipe (correct?)
Upper engine hose to lower radiator?

I have this big-ass surge tank from the cadillac
http://www.v8mr2.com/images/day8/images/PC270081.jpg

Can I use this type of surge tank instead?
http://store.summitracing.com/default.asp?target=partdetail.asp&part=MOR%2D63651&N=120+4294924500+4294921541+304573

What pound caps should I use in the front? and the rear?

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Bill Strong
Racing Strong Motorsports

You are not having a water pump problem. I am for sure of that. You could very easily have a alot of air in the system. I have done over 8 conversions so far and this is a problem. I have made my own bleeding system on all of my cars. If you were closer I could show you the problem. Good luck with your car. They are alot of fun.

Chris Moore
1987 Fiero GT Northstar
1988 Fiero GT T-TOP 3.4 5 speed

okay.... I know my water pump is okay.
Can you discribe or show your hose layout for the northstar with your expansion tanks?

quote Originally posted by Bill Strong: okay.... I know my water pump is okay. Can you discribe or show your hose layout for the northstar with your expansion tanks?

https://www.fiero.nl/forum/Archives/Archive-000001/HTML/20041015-2-051090.html

very cool post...

okay... on the Fiero...
where does the right hose go? Left Hose?
my radiator is like this
right is on the bottom
left is on the top

I am thinking that the thermostat side should suck from the bottom feed on the radiator
and the outlet on the engine should flow to the top feed of the radiator.

I am not a cooling system expert... I am learning as I build

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Bill Strong
Racing Strong Motorsports

That is correct

Thank you VERY much!!!

The upper connection on the engine connects to the upper radiator connection. The lower connection on the engine (with thermostat) connects to the lower radiator connection.

Anything new Rockcrawl?

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Bobby from NW Indiana
93 Northstar and 5 speed Getrag
219customs@verizon.net
My 86 GT build thread
MY 88 Northstar build thread

So, what was it?

The Water pump, or it needed more bleeding on the system?

JG

Must have been air in the system. It has been running for over 6 months now with no problem. I've also completed another Northstar swap and I didn't have any problems with that one. Both are using the Fiero overflow at the front of the car and a sealed cap at the rear just like a stock Fiero, so that system will work. A purge tank in the rear may help to speed the process of bleeding air, but it isn't absolutely necessary. I prefer to keep the engine compartment unclutterd and simple.... plus it makes more room for turbos and such

My N* car has the Fiero purge in front with stock Fiero cap. In the rear I have a modified 4 banger thermostat housing for the filler. It has the bottom cut off and an end of a stock coolant tube welded on. I run the N* thermostat and nothing in the 4 banger housing. Hose runs from the engine to the housing then another connects it to the stock Fiero tube. I have run the car in all kinds of conditions and not had an overheating problem.

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Signature courtesy of MinnGreen.

quote Originally posted by rockcrawl: Must have been air in the system. It has been running for over 6 months now with no problem. I've also completed another Northstar swap and I didn't have any problems with that one. Both are using the Fiero overflow at the front of the car and a sealed cap at the rear just like a stock Fiero, so that system will work. A purge tank in the rear may help to speed the process of bleeding air, but it isn't absolutely necessary. I prefer to keep the engine compartment unclutterd and simple.... plus it makes more room for turbos and such

Good. Bleeding the system like that is a little bit of a trick, but once bled it's fine.

You know, this is wierd..... Now I'm having the same problem.

I'm planning a trip tomorrow, so this might be a problem....

At idle, the radiator (and hose) is cool to the touch, but the coolant tube (driver's side) is hot. Rev it up a bit, and the driver's side hose heats up, and the radiator starts spitting out hot air, and the temp drops..... I've got the same setup as FieroSTS, basically a stock system.

Does this just mean the radiator hose is holding some air???? Should I warm it up, and try to release the air?

I just tried the ogre's bleeding method, opened the rad cap, water came out... okay good... Close it up, park nose downhill, fill from back as the thermostat opens up...

It seems as though if it's just that radiator hose, that the air bubble won't come out unless I park the passenger's side on a curb

I use an apparatus like this back at the fill point in the engine compartment. I fill the system until the radiator overflows and then cap the radiator. Then run the car with the funnel mounted on the fill point and a head of liquid in the funnel. On my Quad 4 the fill point is an in-line tee and I use a 27-29# cap on it. It takes about 15 minutes for the air bubbles to stop.

Maybe I'm missing something but my take on radiator caps is that they are just a pressure-vacuum vent. They can't distinguish between vapor and liquid. They just feel pressure one way or the other. As the system heats up the liquid in the system will expand about 5%. This thermal expansion of the liquid causes the system pressure to build until it opens the radiator cap and pushes liquid (and any compressed air that has collected in the top of the radiator) into the coolant tank. When the system cools down the liquid shrinks and the system pressure goes to vacuum. The vacuum mechanism in the radiator cap opens and liquid off the bottom of the coolant tank is drawn back into the radiator. This cycle of purging to the coolant tank (note that they mark the level for hot and cold) should keep the system basically liquid full.

A problem arises if you get too much air in the system. Then as the liquid heats up and expands it is just compressing air in the system and the system pressure may not get high enough to open the radiator cap to get rid of the air. In this case the top of the radiator will be blanked off by air and the effective surface area to cool liquid is reduced. Of course if it gets bad enough coolant will get so hot that it boils and that will cause the radiator cap to open but you'd probably also be throwing liquid and vapor out the coolant tank cap.

A natural place for air (or combustion gas leaks) to collect in a Fiero system is on the top of the radiator. It seems like that's where the coolant tank needs to be. A second place is back in the engine compartment. What you want is for the coolant outlet hose from the head to be higher than the heads (note how the Fiero water necks are designed). This ensures that the heads run full of coolant and any air ends up at the high point in the outlet hose. If air collects in the coolant outlet hose, I believe the velocity is high enough that it will be transported as a two phase mixture back to the radiator. There is will be eliminated through the previous described purge process.

Something else that might help would be to drill your thermostat -- that is if your thermostat doesn't have an air-bleed hole already in it. Most factory units do, most aftermarket units do NOT. You don't want this hole any larger than 1/16" or it effects the operation (warm-up time) of the engine/cooling system.

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power corrupts. absolute power corrupts absolutely.

Custom Computer Tuning | Engine Conversions | Turbocharging | www.gmtuners.com

quote Originally posted by sanderson: A problem arises if you get too much air in the system. Then as the liquid heats up and expands it is just compressing air in the system and the system pressure may not get high enough to open the radiator cap to get rid of the air. In this case the top of the radiator will be blanked off by air and the effective surface area to cool liquid is reduced. Of course if it gets bad enough coolant will get so hot that it boils and that will cause the radiator cap to open but you'd probably also be throwing liquid and vapor out the coolant tank cap.

Which is why I like to run lower pressure caps...