GN overheats, FMIC...

DeltaBravo

Retired U.S. Army/Navy
Joined
Jun 14, 2014
My GN overheats!…230 degrees is the highest I’ve seen before I pull over and let her cool down.

Lingo- “highway speeds” = 65-70 mph and “city speeds” = 25-35 mph.

Conditions- All temps are referenced from scan master. I live in Southern California by Barstow, temp is 85-95 degrees. Car runs strong, no leaks with mild tune.

History- PO installed a front mount intercooler (F250 power stroke) , an F-body radiator and dual fans.

What I’ve experienced- The fans kick on at 170 and turns off at 162 and will continue this cycle at idle sitting in my drive way. While driving a city speeds, temp lingers around 180-190…if I get on it, the temp does shoot up into the 200 range but does come back down after driving at city speeds.

At high way speeds and flat ground the temps are in the 200 range, usually 205-215. But once I hit a slight uphill grade, the temp slowly start climbing. I will usually slow down to about 40 mph (cruise with the trucker’s) and the temp will hold at 230 until I creese the hill and start coasting on the back side. The temp will drop down to 190 or so at highway speed going down hill.

What I’ve checked- Radiator fluid is clean, coolant/water ratio is about 20/80 respectively. With the cap off and car at operating temp, I can clearly see fluid moving through the three cores of the radiator…so I know my pump and thermostat are working but I don’t know if they are working efficiently…

My theory- So based on the simple fact that like most things, air will take the path of least resistance. Because their wasn’t any radiator shrouds present, my theory is the air is entering passed the grill and because there isn’t anything to force it into the intercooler, condenser, and radiator, it’s simply diverging down and underneath the car and around the side of the intercooler. If any is getting pushed through the intercooler it isn’t much and then that small amount now has to cool down the condenser and radiator. I decided to make my own shrouds and see if it helps. Please see pics… Well, It didn’t! I’m not sure if my design was the cause of this theory not working or if it may be something else.

What next?
 

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man i know that ps cooler is bigger than the radiator i wonder if its backing too much flow to it.
 
man i know that ps cooler is bigger than the radiator i wonder if its backing too much flow to it.


Dunno...? I know others are running FMIC and cruising without over heating...so I'm just curious if there is a 'trick' to the install? or maybe I have another problem.

Thanks for the input.
Damon
 
...................................What next?

Here is what I would do:

First, dump the coolant and use RMI-25 radiator additive and filtered or distilled water. The surficant in RMI breaks down surface tension for better heat transfer.

Plain water is one of the best liquids for heat transfer, much better than antifreeze. In many cases operating temps in a GN has been reduced 15-20 degrees going from A/F to just water and RMI.

Second, get rid of the POS F-Body plastic radiator and get a high efficiency copper core, or a known good quality alum one that has proven results.

Third, check the specs on your fans to assure they are capable of moving enough air to do the job, many are not?

One of my street cars with a 4.1 stroked engine, TE-45A turbo and a PS intercooler will cruise at 65 MPH in 105 deg. temps with AC on and only using one fan, and each is rated at 1000 CFM.

Start by spending $10 for RMI, get rid of the antifreeze, and see how much that will help. :)
 
Here is what I would do:

First, dump the coolant and use RMI-25 radiator additive and filtered or distilled water. The surficant in RMI breaks down surface tension for better heat transfer.

Plain water is one of the best liquids for heat transfer, much better than antifreeze. In many cases operating temps in a GN has been reduced 15-20 degrees going from A/F to just water and RMI.
Agreed...I came from Alaska, were I purchase the car, and the ratio was 70/30 antifreez and water respectively, got to protect from those -40 degrees days (stored in the garage). It was "acting" the same up there. Obviously during the summer months...80-90 degree days. So I figured to change the ratio to 20/80 (a significant change) when I got here but the overheating didn't change.

Second, get rid of the POS F-Body plastic radiator and get a high efficiency copper core, or a known good quality alum one that has proven results.
That's what I'm thinking...it's either that or convert to a stock location Intercooler!

Third, check the specs on your fans to assure they are capable of moving enough air to do the job, many are not?
I've looked all over that damn dual fan and can't find any brands or marking! Wonder what or where it's from?

One of my street cars with a 4.1 stroked engine, TE-45A turbo and a PS intercooler will cruise at 65 MPH in 105 deg. temps with AC on and only using one fan, and each is rated at 1000 CFM.
I want' it! please....

Start by spending $10 for RMI, get rid of the antifreeze, and see how much that will help. :)
I did add a "water wetter" when I changed the ratio. Not RMI...another brand.
 
Sounds like your high speed fan isn't coming on. If you have an after market fan harness with relays and fuses, check the fuses. Also could be the radiator fan switch on the front of the intake. I've had both issues resulting in symptoms like you are having. Do you have a 185 degree thermostat? Is this a new occurance? Do both fans turn on with the A/C? If so then drive with the A/C on and see if the temp stays under 200.
 
Also, pull the thermostat out. No need for it in cally weather.
 
Here's another suggestion:

Make sure you have some sort of weather stripping or sealing strip around the perimeter of your fan housing, so the housing will fit snuggly and that there is no gap for air to escape between the fan housing and your radiator. This way you'll be sure that your fan is pulling all the air available thru the radiator core. Should help.
I used an old trunk weatherstrip which did the trick for me!
 
Checked for a stuck thermostat? I have had them stick slightly open slightly and show similar symptoms. Is the thermostat installed backwards? Have you left the cap off and watched the water flowing? How old is the water pump?
 
Hey Damon, will you be at the swap meet on the 10th?
I will be going with my Tahoe full of parts, you have a longer haul than me!
Let me know if you want to share a ride we can discuss the solutions to the cooling problems.
Nick will be there also.
Steve

I hope you did not get stuck in the traffic like I did after the cruise last weekend! That tests the limits of a cooling system!
 
Check for the radiator box in parts. Its very common for people to install a FMIC and discard the lower section. Without the box in parts the air will simply hit the FMIC and then take the path of least resistance and go out the bottom of area and bypass the radiator. I ran a F Body radiator with a FMIC and stock fan for 10 years without any overheating issues. This was in the hot humid South.
 
Sounds like your high speed fan isn't coming on. If you have an after market fan harness with relays and fuses, check the fuses.

I'm not sure but will look into that.


.Also could be the radiator fan switch on the front of the intake. I will check that....maybe order a new one. 've had both issues resulting in symptoms like you are having. Do you have a 185 degree thermostat? Dunno, but I've order a 160. Is this a new occurance? No Do both fans turn on with the A/C? Dunno, I will check. If so then drive with the A/C on and see if the temp stays under 200.

Thanks for the tips
Sounds like your high speed fan isn't coming on. If you have an after market fan harness with relays and fuses, check the fuses. Also could be the radiator fan switch on the front of the intake. I've had both issues resulting in symptoms like you are having. Do you have a 185 degree thermostat? Is this a new occurance? Do both fans turn on with the A/C? If so then drive with the A/C on and see if the temp stays under 200.
 
Hey Damon, will you be at the swap meet on the 10th?
I will be going with my Tahoe full of parts, you have a longer haul than me!
Let me know if you want to share a ride we can discuss the solutions to the cooling problems.
Nick will be there also.
Steve

I hope you did not get stuck in the traffic like I did after the cruise last weekend! That tests the limits of a cooling system!


I don't know if I will make it, but I'm going to try. As far as traffic goes, my GN does fine in the slower speeds but at higher speeds it's overheating.
 
A car i recently sold is still running the cooling system and the RJC mega cooler (4.75" thick intercooler) I had in the car. Its a cheap 3 row alum radiator with dual fans. No special sealing (additioanl rubber stripping) of any thing and has all of the factory shrouding removed (except the black plastic horizantal piece affixed to teh grill). Its running a stock waterpump. This car just recently completed 1100 miles of drag week with an average ET under 9 seconds. This car also pulled a trailer the entire time, from track to track, and never over heated. When I owned the car it rarely went above 180 even when on the dyno. This was even with out a supplemental shop fan blowing on it.

Based up on that information, i am going to say your FMIC is not the problem.

I would like to ask the condition of the radiator cap? Have you conducted a coolant pressure test on that cap, does it hold pressure? A failed radiator cap could also induce the issues you are having .... just a thought. Ive seen this simple part of the equation overlooked many many times.

Sam
 
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Have you checked the AC system ? An incorrectly filled or failing system will produce much more heat across the condenser.

Bryan
 
The fans do nothing at highway speeds. Again how is the water flowing out the tubes? I believe water flow is the issue. As mentioned clogged rad will do this, had it on several other cars, t stat stuck,in backwards. Leave the cap off when it's cold and crank it up and see how the water flows.
 
A car i recently sold is still running the cooling system and the RJC mega cooler (4.75" thick intercooler) I had in the car. Its a cheap 3 row alum radiator with dual fans. No special sealing (additioanl rubber stripping) of any thing and has all of the factory shrouding removed (except the black plastic horizantal piece affixed to teh grill). Its running a stock waterpump. This car just recently completed 1100 miles of drag week with an average ET under 9 seconds. This car also pulled a trailer the entire time, from track to track, and never over heated. When I owned the car it rarely went above 180 even when on the dyno. This was even with out a supplemental shop fan blowing on it.

Based up on that information, i am going to say your FMIC is not the problem.

I would like to ask the condition of the radiator cap? Have you conducted a coolant pressure test on that cap, does it hold pressure? A failed radiator cap could also induce the issues you are having .... just a thought. Ive seen this simple part of the equation overlooked many many times.

Sam


Sam,

I don't have a way to check the radiator cap or do a leak down test of any sort. I'm thinking of purchasing a tool for that reason...I'd rather invest in something that will help determine the actual problem instead of just throwing parts in.

I will not be able to do any work on her this weekend, but in the mean time...I'm thinking of getting a radiator leak down test tool and report back. Thanks for the advise
Damon
 
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