Yet Another Running Hot Thread

[Flyin Brian]

Ok, here goes. Whenever the weather is warmer than 80 degrees out my car always seems to get up to 200 degrees no matter what. I know 200 is not that hot, my new Tahoe quickly goes to 210 and stays there every time I drive it but it is supposed to. I figure I should be able to get my car to stay closer to 180 if everything is working right. I am starting to suspect the radiator is not flowing as good as it should. I removed the radiator cap and removed fluid until I could see the top of the oil coolers and started it up. When the thermostat opened the water level dropped very quickly but was not exactly blasting back through the tube ends. Once it got hot enough that the thermostat was staying mostly open the water was flowing but not that fast. If I rev the engine it flows out a little better but not exactly blasting through like most people say it should. I guess my question is how good should the water be coming through the tubes when the thermostat opens? Should it immediately start shooting out of all of the visible tubes when the thermostat opens and the level drops??

I will now list my combination, history, and things I have tried that did not work. It will be lengthy but my main question is about the water flow as that is what I am suspecting is the problem.

Combo not listed in my sig.
Motor rebuilt 700 miles ago, ran hot on all previous rebuilds too.
GN1 super extreme front mount. I know that hurts cooling ability.
GN1 2.5" aluminum radiator. Had it for 4 years. Ran antifreeze and water for the first 3 years, switched to RMI 25 a year ago and it seemed to help a lot. Recently put a new bottle of RMI 25 in and it did not make any difference this time. Radiator has never been flushed. There is a small amount of visible corrosion on some of the tube ends near the radiator cap.
Dual SPAL fan setup that comes on at 170. Both fans moving a ton of air.
160 degree thermostat that I have checked several times. It opens fully at 160.
Stock auto store water pump that is 2 years old.
I am running the turbo saver and not using the motor oil cooler in the radiator.
Transmission fluid goes through the radiator first and then through a large external cooler. Transmission fluid temps eventually reach 200 as well. I don't like that either.
I am reading temperature on the power logger as well as a VDO gauge and they both read about the same.


Things I have tried that did not work.
I took the thermostat out last summer. Took longer to warm up but still got to 200.
Completely boxed in radiator. Did not make any difference, not even on the highway.
Removed the seal strip at the top of the firewall to let some heat out. Helped very little.

When I go for a drive I usually start with the AC on and go for a cruise. After the engine gets good and warm and the oil pressure drops to 20 at idle in drive I know everything is hot. Then the temp just starts creeping up until it gets to 200 to 205 and the trans fluid eventually reaches 200 as well. I am reading the trans fluid temp in the pan. My drives consist of both traffic and highway cruises. When everything is at 200 I turn the AC off and sometimes crank up the heater to try and help bring the temps down. I start heading home and taking it easy on the throttle. 10 minutes later I am home and the temp may have come down to 195 or 190 if it is not too hot outside (90). When I get home I open the hood and let it idle for a while. Fans run continuously and the car does not cool down much more until I turn it off. Top radiator hose is pressurized and stays that way for a long time after shutting off.

It seems like this car has always run hot. It ran hot with the stock radiator, stock fan, SLIC, and my first motor. I put in a new stock type radiator from Postons and that seemed to help a lot. I switched to the large FMIC, aluminum radiator, and dual fan setup at the same time but it still ran a little hot. I can't remember how hot as that was 4 years ago and I had less instrumentation back then.

I am thinking my next step is to remove the radiator and do a thorough cleaning and back flush to see if any crud comes out. Maybe borrow an inspection camera so I can look at the tube ends on the thermostat end of the radiator and see if there is any corrosion or blockage. Next I may consider a better water pump but historically whenever I had a car running hot and I put on a trick aluminum water pump it made no difference. I could go with a different radiator as well I guess if that would help. I would like to keep the FMIC as it works really well and I don't want to switch back.

Sorry for the length of this post but I just want to be able to cruise around on a hot summer day with the AC on and keep my temps closer to 180. I think this is possible?

Thanks.

 

[Nick Micale]

...... If I rev the engine it flows out a little better but not exactly blasting through like most people say it should. I guess my question is how good should the water be coming through the tubes when the thermostat opens? Should it immediately start shooting out of all of the visible tubes when the thermostat opens and the level drops??................................Thanks.

The only replacement radiators I have personally had problems when persistent over heating was an issue in a GN have been with a couple off-shore aluminum replacements.

I do not know the supplier or whose supplied them, but they had a basic design flaw which I determined after replacing everything in the cooling system, including the dual fans.

The last item I changed was the alum radiator which was replaced with a new high-efficiency copper core unit that I have used for years.

Looking at the size of the tubes in the alum radiator, I could see they were very wide, but also VERY small vertically, and restricted flow big-time.

After installation of the copper radiator temps went from 220-230 on a summer day, to 185-190 when cruising!

 

[Flyin Brian]

Thanks Nick. I was wondering about that. I have been doing some research on radiator tube designs lately and there are of course many different opinions. Lots of people talk about some 3 core radiators not having as much tube area as a proper 2 core due to tube size. They say the proper 2 core has tubes that are 1" wide while many 3 core units have tubes that are .625" wide so the proper 2 core actually has more tube area. I don't know about this. My radiator has 3 cores or rows of tubes and they appear to be 5/8" wide and are very small vertically. If the tubes are the restriction I guess a higher flowing design water pump could force more water through the tubes but this seems like a band aid fix if the design of the radiator core is not optimal to start with.

I know radiator type and design make a big difference. On my old Tahoe I replaced the stock radiator when it sprung a leak. I bought the bigger core replacement at the auto store as that is what I thought I had. When I got home and started taking the old radiator out I noticed the core was thinner than the new one. It cooled WAY better.

 

[turbofrank]

Which chip ?

 

[Flyin Brian]

SD2. I thought I had it running to lean at idle (13.5:1 gas AFR) but I changed it to 12.5:1 at idle and it ran just as hot.

 

[hotairgnx548]

SD2. I thought I had it running to lean at idle (13.5:1 gas AFR) but I changed it to 12.5:1 at idle and it ran just as hot.

Brian I've ran a griffin alum radiator for years. 160 stat, cheapie dual elect fans, individual cockpit mounted 25 amp on off switches. In summer temps one fan running 170/173 degrees> If I get caught in bumper to bumper traffic I have the option to turn on the second fan. John

 

[rodruckus]

Have you tried a Flow Kooler high flow water pump? I run one with a stock 30yo rad/fan, regular 50/50 water/antifreeze mix(no additives), and a 160°thermostat. I typically run at 162°-163° and spike at 167° for a moment when my fan kicks on. The highest I've ever registered on my scanmaster was 179° after several consecutive wot 100mph hits. When I began driving normal again within minutes I was down at 172°, then back to 162°-163° in 15 minutes. It's funny how it seems that so many people go to such extremes upgrading their cooling system, but neglect its weakest link; an antiquated water pump.

 

[rodruckus]

You should go to the Flow Kooler website, it's highly educational in regards to the science of cooling and components. He has this whole science thing behind his water pumps and claims you can even gain hp with one. You gain hp, because you use less to turn it. And at the same time, improving your flow efficiency will conserve your hp. Plus, if you're running a thinner core aluminum rad they go hand and hand. He can even fab copper rads and intercoolers, fan shrouds and heater cores. All made in the USA.

 

[Flyin Brian]

Have you tried a Flow Kooler high flow water pump? I run one with a stock 30yo rad/fan, regular 50/50 water/antifreeze mix(no additives), and a 160°thermostat. I typically run at 162°-163° and spike at 167° for a moment when my fan kicks on. The highest I've ever registered on my scanmaster was 179° after several consecutive wot 100mph hits. When I began driving normal again within minutes I was down at 172°, then back to 162°-163° in 15 minutes. It's funny how it seems that so many people go to such extremes upgrading their cooling system, but neglect its weakest link; an antiquated water pump.

I have looked at the Flow Kooler but have not tried one yet. It looks like a nice product.
Do you have any before and after temps with your old water pump?
Was it running hot before you installed the Flow Kooler?
What was the ambient temperature with your above numbers?
Were you running the A/C?
Do you have a front mount intercooler?
Thanks for the info.

 

[rodruckus]

I run the same numbers winter or summer, 162°-163° when driving normally. When I hit that 179° number, I was on it hard during a dry day in the mid-high 80s. I have 150k mi with no a/c, a stock location Spearco liquid i/c and a Chris Alston's Chassisworks Fab 9 rearend with 3.70s and a Detroit Locker; so I tach about 200rpm higher on the freeway. Sorry, no old numbers, but you see how old and stock my system is. Other than the Flow Kooler and 160° thermostat.

If you're running a fmic, I'd try one of his pumps. They're fairly inexpensive(not cheaply made) and they work. Also, they're highly recommended for stop and go driving, parades, and in line at car shows, where air flow is nil. Similarly to a fmic, just the pump alone will keep you running cool. No mods, direct bolt in replacement.

 

[Flyin Brian]

Thanks, I may have to try one.

 

[NY_GN]

Ok, here goes. Whenever the weather is warmer than 80 degrees out my car always seems to get up to 200 degrees no matter what. I know 200 is not that hot, my new Tahoe quickly goes to 210 and stays there every time I drive it but it is supposed to. I figure I should be able to get my car to stay closer to 180 if everything is working right. I am starting to suspect the radiator is not flowing as good as it should. I removed the radiator cap and removed fluid until I could see the top of the oil coolers and started it up. When the thermostat opened the water level dropped very quickly but was not exactly blasting back through the tube ends. Once it got hot enough that the thermostat was staying mostly open the water was flowing but not that fast. If I rev the engine it flows out a little better but not exactly blasting through like most people say it should. I guess my question is how good should the water be coming through the tubes when the thermostat opens? Should it immediately start shooting out of all of the visible tubes when the thermostat opens and the level drops??

I will now list my combination, history, and things I have tried that did not work. It will be lengthy but my main question is about the water flow as that is what I am suspecting is the problem.

Combo not listed in my sig.
Motor rebuilt 700 miles ago, ran hot on all previous rebuilds too.
GN1 super extreme front mount. I know that hurts cooling ability.
GN1 2.5" aluminum radiator. Had it for 4 years. Ran antifreeze and water for the first 3 years, switched to RMI 25 a year ago and it seemed to help a lot. Recently put a new bottle of RMI 25 in and it did not make any difference this time. Radiator has never been flushed. There is a small amount of visible corrosion on some of the tube ends near the radiator cap.
Dual SPAL fan setup that comes on at 170. Both fans moving a ton of air.
160 degree thermostat that I have checked several times. It opens fully at 160.
Stock auto store water pump that is 2 years old.
I am running the turbo saver and not using the motor oil cooler in the radiator.
Transmission fluid goes through the radiator first and then through a large external cooler. Transmission fluid temps eventually reach 200 as well. I don't like that either.
I am reading temperature on the power logger as well as a VDO gauge and they both read about the same.


Things I have tried that did not work.
I took the thermostat out last summer. Took longer to warm up but still got to 200.
Completely boxed in radiator. Did not make any difference, not even on the highway.
Removed the seal strip at the top of the firewall to let some heat out. Helped very little.

When I go for a drive I usually start with the AC on and go for a cruise. After the engine gets good and warm and the oil pressure drops to 20 at idle in drive I know everything is hot. Then the temp just starts creeping up until it gets to 200 to 205 and the trans fluid eventually reaches 200 as well. I am reading the trans fluid temp in the pan. My drives consist of both traffic and highway cruises. When everything is at 200 I turn the AC off and sometimes crank up the heater to try and help bring the temps down. I start heading home and taking it easy on the throttle. 10 minutes later I am home and the temp may have come down to 195 or 190 if it is not too hot outside (90). When I get home I open the hood and let it idle for a while. Fans run continuously and the car does not cool down much more until I turn it off. Top radiator hose is pressurized and stays that way for a long time after shutting off.

It seems like this car has always run hot. It ran hot with the stock radiator, stock fan, SLIC, and my first motor. I put in a new stock type radiator from Postons and that seemed to help a lot. I switched to the large FMIC, aluminum radiator, and dual fan setup at the same time but it still ran a little hot. I can't remember how hot as that was 4 years ago and I had less instrumentation back then.

I am thinking my next step is to remove the radiator and do a thorough cleaning and back flush to see if any crud comes out. Maybe borrow an inspection camera so I can look at the tube ends on the thermostat end of the radiator and see if there is any corrosion or blockage. Next I may consider a better water pump but historically whenever I had a car running hot and I put on a trick aluminum water pump it made no difference. I could go with a different radiator as well I guess if that would help. I would like to keep the FMIC as it works really well and I don't want to switch back.

Sorry for the length of this post but I just want to be able to cruise around on a hot summer day with the AC on and keep my temps closer to 180. I think this is possible?

Thanks.

I had same issue, changed thermostat, added rmi 25 after radiator flush, turned on heater the whole nine.

Temps still creeped up to 210 and above.

Added Casper fan switch, when I run the high speed fan it never gets over 180.

Even put in high speed switch for looks.

 

[Flyin Brian]

I am running the dual SPAL 12" fans with the Casper's harness. Both fans come on at 170. Unless the weather is cool they never turn back off.
I can drop a sheet of paper in front of my grill when the fans are on and they will suck it up to the grill and hold it there. I feel like air flow is not the problem.
I am thinking it is a problem on the liquid side. I may swap my copper brass radiator back in to see if that makes any difference. It is one I bought new at Poston's back in the day. Only ran it for a couple of years so it is still like new.
I can clean and inspect my aluminum radiator while it is off. If both radiators work equally bad I may try the FlowKooler water pump. If none of that works I will get a better radiator from Nick or Alradco.

 

[JYLP]

I had that issue and I had an $800 flex-a-lite cooling system with a high volume, high flow pump. Fan would suck paper to the front mount and everything, but it still ran hot. Took the 160 out, ran straight water and still ran hot even driving normal, just took longer. Got all the air out of the system and still ran hot. I took that radiator off, put an F body radiator on and went to the junkyard with only my trusty multi-tool and got the dual fans off a 300m. At the track, I see 173F with just 50/50 coolant. It doesn't run cool now, it runs cold... I have to set the fans to come on at like 180F and shut off at 170F when it's cool out just to have heat in the car and yes, I put the 160 back in. It isn't even boxed in. So for about $120 my cooling problems were solved AND I knocked a few pounds of nose weight off the car in the process. Doing more with less

 

[Flyin Brian]

The only replacement radiators I have personally had problems when persistent over heating was an issue in a GN have been with a couple off-shore aluminum replacements.

I do not know the supplier or whose supplied them, but they had a basic design flaw which I determined after replacing everything in the cooling system, including the dual fans.

The last item I changed was the alum radiator which was replaced with a new high-efficiency copper core unit that I have used for years.

Looking at the size of the tubes in the alum radiator, I could see they were very wide, but also VERY small vertically, and restricted flow big-time.

After installation of the copper radiator temps went from 220-230 on a summer day, to 185-190 when cruising!

I am pretty sure this was the problem Nick. I finally removed the radiator and devised a simple flow restriction test using a shop vac and a homemade manometer. I checked my old Postons replacement radiator against my off shore aluminum radiator and it was obvious. The aluminum radiator had about double the flow resistance as the other radiator. The tubes are very small vertically and restrict flow as well as plug very easily.

I installed that aluminum radiator at the same time as I installed my front mount ID and it always ran warm after that. I assumed it was the front mount but I am sure now it was the bad radiator design. I will be putting the old Postons radiator back in since it is in good shape until I can afford a proper new radiator.

Another hard lesson learned.

 

[Chuck Leeper]

In the "FWIW" dept....
My experience w/ plastic fans on industrial engines, [lift trucks], has shown, that heat cycling eventually causes the plastic blades to lose their "set". As the blades flatten out, they drop the ability to move air....[30 yo TR fans comes to mind].
Some have even gone so far as to break off...We all know what that means.

 

[GNRick]

What's wrong with the Postons radiator? If it works why not leave it in there?

 

[Flyin Brian]

What's wrong with the Postons radiator? If it works why not leave it in there?

Nothing really, was only in the car for a couple of years. I originally bought the aluminum radiator because I thought it would cool better and it is a little lighter than the Poston's radiator.
I will probably run the Poston's indefinitely if it cools ok.