1988 Fifth Avenue Cooling System Performance

GamblerSeanAZ

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Looking for insights to the stock cooling system performance in hot climates, up long highway grades.

I took my 1988 Fifth Avenue on its first road trip after the Holley 2300 and GM HEI conversion on the 318. The engine seems to run just fine, and I don't notice any general problems with the cooling system after I replaced the fan clutch. I'm in Arizona, so we can assume the ambient temperature was 100 degrees. The temp gauge generally stayed right in the middle, except for on some long grades. By the end of a 7 mile, 6% grade, with the A/C turned off, and running in second gear at 55 MPH, the temp gauge was just a hair past the last tick mark before the H. After the hill, the temp gauge returned to normal.

Is this typical cooling system performance for these cars? If not, where should I begin to focus my attention for upgrades or replacement parts? Is there a common radiator upgrade for the M-bodies? Discuss :)
 

Mikes5thAve

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Have you done a coolant change lately? How do the fins look thru the rad cap hole? It sounds like its' working normally and it's the heat and extra load that made it run hotter then usual.
If that sort of driving condition is a regular occurance a 7 blade fan and changing to a truck radiator would help. Both are direct bolt in altho these days the replacement type rads are the plastic and aluminum ones not the traditional style.
 

LSM360

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That's pretty hot. I've never had a gauge show that high. I wouldn't want to run at that temp very long, although I don't know what the actual temp would be. Did you need to be running in 2nd gear once you got up to speed? That might have had you at more rpm's than necessary and added to the heat.

As Mike wrote, I'd check the fins inside and out, make sure your coolant is not super old and weak, and if so do a 50/50 coolant and distilled water change, but that's more about protection than running cooler. Also as Mike mentioned, some people go to the truck radiators, but so many of the new radiators are crap, so a recore probably better if your radiator is bad.
 

GamblerSeanAZ

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Have you done a coolant change lately? How do the fins look thru the rad cap hole? It sounds like its' working normally and it's the heat and extra load that made it run hotter then usual.
If that sort of driving condition is a regular occurance a 7 blade fan and changing to a truck radiator would help. Both are direct bolt in altho these days the replacement type rads are the plastic and aluminum ones not the traditional style.

The car is fairly new to me, and I only have maybe 500 miles on it myself. The radiator looks ok, but not as clean as a new one. I haven't done a coolant change yet, so I'll give it a flush and some fresh 50/50 and see what happens. It's a hobby car for me, so it's nothing that needs critical attention, but I do plan to take it out on more weekend trips, so I'd like to give it some attention. Thanks for the tips on the truck radiator and fan - I'll look into that. Appreciate the reply.
 
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GamblerSeanAZ

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That's pretty hot. I've never had a gauge show that high. I wouldn't want to run at that temp very long, although I don't know what the actual temp would be. Did you need to be running in 2nd gear once you got up to speed? That might have had you at more rpm's than necessary and added to the heat.

As Mike wrote, I'd check the fins inside and out, make sure your coolant is not super old and weak, and if so do a 50/50 coolant and distilled water change, but that's more about protection than running cooler. Also as Mike mentioned, some people go to the truck radiators, but so many of the new radiators are crap, so a recore probably better if your radiator is bad.

The car wouldn't hold speed in 3rd up a 6% grade with two 250lb guys, an ice chest full of b... soda, and a trunk full of tools, spare tire, supplies, etc, especially with the 2.2X:1 rearend ratio. Not sure what the true temperature or RPMs were. I agree that's way too hot, thus my concern. Thanks for the tips - I'll check into those items, and see how it responds. I'll look into a truck radiator too.
 

Camtron

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I haven’t taken my car up a grade as Illinois is flat and boring as all hell, but on a 150 mile trip with a 383 big block in my trunk, in the middle of 98 degree summer day, my temp gauge never even hit the halfway mark. I just have a stock cooling system.
May be due for a coolant flush. there was so much rust/sludge in the block the first time I flushed my cars cooling system. Made quite a difference in making the temp gauge read stable without fluctuation afterwards.
 

GamblerSeanAZ

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I haven’t taken my car up a grade as Illinois is flat and boring as all hell, but on a 150 mile trip with a 383 big block in my trunk, in the middle of 98 degree summer day, my temp gauge never even hit the halfway mark. I just have a stock cooling system.
May be due for a coolant flush. there was so much rust/sludge in the block the first time I flushed my cars cooling system. Made quite a difference in making the temp gauge read stable without fluctuation afterwards.

AZ is full of mountains, so it's not a good comparison of results - my trip was 154 miles with a 5883 foot elevation increase, but I see what you're getting at. The common thread in everybody's replies so far is flushing the cooling system, so I'll start there and see what happens. Thanks for the advice! What did you put the 383 into?
 

Camtron

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AZ is full of mountains, so it's not a good comparison of results - my trip was 154 miles with a 5883 foot elevation increase, but I see what you're getting at. The common thread in everybody's replies so far is flushing the cooling system, so I'll start there and see what happens. Thanks for the advice! What did you put the 383 into?
Oh, I’m aware. I lived in Phoenix/Tempe for 9 years. The 383 got put into my garage. It will find its way into my Fifth Ave one of these years.
 

Aspen500

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As long as it doesn't overheat or constantly run that hot, it's not the end of the world. Of course were talking stock gauge and accuracy can be sketchy.
MY Aspen (500") generally runs about center on the gauge in 90 degree temps with the A/C cranked. Ont the way to and from work there's one hill that's STEEP and long. Maybe 400 foot rise up and back down in under a mile. Then, the gauge will creep up to about 3/4 or maybe a bit higher if it's humid. By the time I coast, in 2nd gear to hold the 35 mph speed limit, it's back to 1/2 and stays there.

Adding a bottle of water wetter can do wonders for engine temps. It breaks the surface tension and allows better heat transfer to and (more importantly) from the coolant to the radiator tubes so the air can remove more heat.


I assume the fan shroud is present, yes? Sometime's what helps is an air dam below the radiator lower yoke to direct more air up and through the radiator rather than just going under the car. I do know some vehicles would overheat if it was missing (i.e. mid to late '80's Camaro's and Firebird's). Usually though, that cars with little to no grille opening but it can help any car.

Being in Arizona and not having to worry too much about below zero temps, going lighter on the coolant mix helps. Maybe 30/70 (anti-freeze/water). Plain water transfers heat better than glycol does, although the downside is it will boil at a lower temp. Double edged sword, lol.

41FAcmsBhfL._SL500_AC_SS350_.jpg
 

Camtron

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Premature post! Fat fingers. Making a joke about you living in this oven for 9 years :D
Lol, heat never bothered me. I miss it. I lived by the Phoenix Zoo and had Papago Park right outside my front door to go hiking and mountain biking. I’ll probably move back one of these years. It beats California and Illinois, lol.
 

GamblerSeanAZ

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As long as it doesn't overheat or constantly run that hot, it's not the end of the world. Of course were talking stock gauge and accuracy can be sketchy.
MY Aspen (500") generally runs about center on the gauge in 90 degree temps with the A/C cranked. Ont the way to and from work there's one hill that's STEEP and long. Maybe 400 foot rise up and back down in under a mile. Then, the gauge will creep up to about 3/4 or maybe a bit higher if it's humid. By the time I coast, in 2nd gear to hold the 35 mph speed limit, it's back to 1/2 and stays there.

Adding a bottle of water wetter can do wonders for engine temps. It breaks the surface tension and allows better heat transfer to and (more importantly) from the coolant to the radiator tubes so the air can remove more heat.


I assume the fan shroud is present, yes? Sometime's what helps is an air dam below the radiator lower yoke to direct more air up and through the radiator rather than just going under the car. I do know some vehicles would overheat if it was missing (i.e. mid to late '80's Camaro's and Firebird's). Usually though, that cars with little to no grille opening but it can help any car.

Being in Arizona and not having to worry too much about below zero temps, going lighter on the coolant mix helps. Maybe 30/70 (anti-freeze/water). Plain water transfers heat better than glycol does, although the downside is it will boil at a lower temp. Double edged sword, lol.

View attachment 41039
Thanks for the reply. Yeah, the shroud is present. Not sure if there's an air dam present - I'll look. I'll try some Water Wetter too after a flush to see if that helps.
 

Aspen500

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I was just listing things I've known to help the cooling system. I have seen the water wetter really help quite a bit.

I always wish there was a doable way to monitor cylinder head temp. That's more important than actual coolant temp. What I mean is, the head could be "overheated" while the coolant temp looks fine IF the heat isn't being transfered to the coolant well enough. Never came up with a way to retrofit a cylinder head temp sensor to work with a gauge. All the cyl head temp sensors I know of are made to send a signal to an ECM, not run a gauge. Sorry, rambling and thinking out loud again!:D
 

MARCH374

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What truck Radiator are you speaking of ? Is it a bolt in ? Thanks
 

LSM360

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You could also consider an AHB radiator, but I doubt you'll find one. Also COULD have Glen-Ray recore yours IF IF IF yours is bad. YES it is expensive and your car will be inop for awhile because you have to send it away, but you will NOT find a company with a better reputation for service and quality. And Glen-Ray may be able to increase your radiator's cooling capacity. Also, if you get to where you need a new water pump, PLEASE don't get the MP pump. As much as I like to use all Mopar stuff, they've been having issues with early failures. I would get an HP Milodon pump with anti-cavitation plate. Yes, you'll spend more, BUT better cooling, HD bearings and shaft for long life. Worth it!
 

MARCH374

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You could also consider an AHB radiator, but I doubt you'll find one. Also COULD have Glen-Ray recore yours IF IF IF yours is bad. YES it is expensive and your car will be inop for awhile because you have to send it away, but you will NOT find a company with a better reputation for service and quality. And Glen-Ray may be able to increase your radiator's cooling capacity. Also, if you get to where you need a new water pump, PLEASE don't get the MP pump. As much as I like to use all Mopar stuff, they've been having issues with early failures. I would get an HP Milodon pump with anti-cavitation plate. Yes, you'll spend more, BUT better cooling, HD bearings and shaft for long life. Worth it!
Thanks for the info. What did Glen-Ray charge for a the recore ? Thanks
 

Aspen500

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Glen-Ray built my radiator about 25 years ago. They took the largest Aspen radiator made (360 with A/C I imagine), used the tanks and side brackets and recored with a 3 row. Back then it was about $200, donor radiator included(those were the days!). They do excellent work and added bonus, are huge Mopar enthusiasts. I'm lucky enough to live maybe 7 or 8 miles away from Glen-Ray. They're the best and,,,,,,,,,,,they're the only radiator shop left in this area. After I had my A/C lines mocked up and position marked, I had them do the bubble crimping and brazing a couple adapters to allow me to keep the factory h-block ends at the evap. and condenser also.

I've seen their repop big block and Hemi rads in person. I have a hard time believing the factory original ones ever looked quite as good as their repops.:cool:

I've got a Milodon high volume pump on my car and thumbs up.:)
 
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