V8 conversion overheating at highway speeds

[coop77]

OK, so I have a gremlin that I can't seem to work out no matter what I do... Freshly rebuilt 350 was running Edelbrock aluminum heads and intake, and recently switched for Vortec heads and aluminum air gap. Both setups have overheated at highway speeds (230-ish). I have tried electric fans and am now running the plastic style racing flex fan with correctly fitting shroud. Had 3 core copper radiator rodded, replaced thermostat with multiple temps, checked the system for air, waterpump is new (with motor build) and seems to be flowing well. Engine runs great with timing and fuel set correctly. It has 3 inch exhaust with flow master, so I don't think constriction is an issue. I am having the mechanic who just did the head swap put in an aluminum radiator, but beyond this I'm stumped. Should also mention that I'm using new Speedhut gauges and the outside temps would suggest it is accurate.

Any ideas?

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[dozerking]

Have you shot the motor with a temp gun to make sure it is reading pretty close to what your gauges say? how hot is it where you are when it over heats? If you shoot it with a temp gauge check both upper and lower hoses and see what the difference is when the water cycles they may have messed up your radiator when they rebuilt it! Other than that the only thing I could think of is maybe when you bought your flew fan you got a reverse rotation fan so it spins opposite of your water pump?? You should clearly be able to hear your fan make a bunch of noise when you rev the motor!?

 

[coop77]

Have you shot the motor with a temp gun to make sure it is reading pretty close to what your gauges say? how hot is it where you are when it over heats? If you shoot it with a temp gauge check both upper and lower hoses and see what the difference is when the water cycles they may have messed up your radiator when they rebuilt it! Other than that the only thing I could think of is maybe when you bought your flew fan you got a reverse rotation fan so it spins opposite of your water pump?? You should clearly be able to hear your fan make a bunch of noise when you rev the motor!?

I haven't shot the hoses to check, but I'm guessing if it is the radiator, the new one will fix it... Its been high 90's to low 100's around here when it overheats. The fan moves a ton of air, so I know that it's flowing the right direction. One thing worth mentioning is that is worse with the AC on. With it off it will JUST run within tolerances (195-210). I pressure washed to condenser to try and make sure it was blocked. Maybe it's adding just enough added heat to tip it beyond what the rad can cool?

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[Elbert]

I want to point right at the flex fan... has the truck ever run normal for any length of time? Normal in regard to temps.

I'm running a similar setup... 99 5.7 Vortec.

OEM Style replacement 4 core radiator, GM fan clutch and matching GM fan, custom fan shroud that does not block any of the air crossing the radiator core. On hot days it will run around 200-205-210 under load with the A/C going. Without A/C something less. My fan and fan clutch are the same thing that's on teh GM pickups and SUV with 5.7 ...1999 model year...which I think is the same configuration back to around 1997 or so given the 5.7 vortec engine.

Assume you have a thermostat working and all of that is good.

Its been my experience that those flex fans don't work well and that you have to be int eh rpms around 2500 for the fan to pull any air.

My truck is geared low and I don't drive it that much to start with and not on extended trips on the pavement. But what I've driven I'm dancing around the above numbers (in 5th gear with ac on and Im probally doing 60-65 at max).

 

[dozerking]

elbert I disagree with the last thing you said my motor has never run cooler than with my flex fan and at highway speeds like he is saying the flex fan should be pushing more than enough air but that's just my opinion! You should post a few pics of your engine bay and rad/fan shroud and all that to shine alittle more light for us to better answer your question!!

 

[Elbert]

Once I got my truck setup right....the fan shroud made the biggest difference and I think the factory setup of the GM fan and Fan clutch are hard to beat.

Even then I don't think there is sufficient square inch of radiator capacity to effectively cool a V8 in the LC using the stock size radiator. But given that....normal operating temps with ac off should dance around the thermostat rating (in my case 195F) and under load and with A/C on somewhere 205-215F or so in my view. So far I've been able to stay in that range....and I've been running arould a little at ambient temps in the high 90's.

I can dig around and post some pics of what I've done...which is nothing crazy...my friend is the fabricator guy and helps me out with stuff.

I think generally that you should be under 220F or that's been my goal.

 

[coop77]

I want to point right at the flex fan... has the truck ever run normal for any length of time? Normal in regard to temps.

I'm running a similar setup... 99 5.7 Vortec.

OEM Style replacement 4 core radiator, GM fan clutch and matching GM fan, custom fan shroud that does not block any of the air crossing the radiator core. On hot days it will run around 200-205-210 under load with the A/C going. Without A/C something less. My fan and fan clutch are the same thing that's on teh GM pickups and SUV with 5.7 ...1999 model year...which I think is the same configuration back to around 1997 or so given the 5.7 vortec engine.

Assume you have a thermostat working and all of that is good.

Its been my experience that those flex fans don't work well and that you have to be int eh rpms around 2500 for the fan to pull any air.

My truck is geared low and I don't drive it that much to start with and not on extended trips on the pavement. But what I've driven I'm dancing around the above numbers (in 5th gear with ac on and Im probally doing 60-65 at max).

The truck did run normal... Oddly enough with the smoking, crappy build 305 with a detonated piston it had in it when I bought it. It had a metal fixed blade fan on it (which I've also run on this set up to no avail). I would try a clutch fan, but my whole pulley setup is based on a long waterp ump, and it doesn't appear that there is enough room to not hit the radiator under torque. Also, if you'll note, it's overheating on the highway, not at idle or in town which seems like less of a fan issue to me since at 70-80 mph it should move ample air on its own (I obviously don't know though). That's why I mentioned timing, a/f and exhaust since those seemed most likely to cause overheating at speed, but all seem well based on how well it runs/starts.

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[Elbert]

elbert I disagree with the last thing you said my motor has never run cooler than with my flex fan and at highway speeds like he is saying the flex fan should be pushing more than enough air but that's just my opinion! You should post a few pics of your engine bay and rad/fan shroud and all that to shine alittle more light for us to better answer your question!!

Assume you are talking about my comments on the flex fan. I run A/C and run off road quite a bit... in my view a flex fan has a very narrow rpm range under which it pulls air. When operational it pulls air pretty good, when not "operational" it does not. THere are different versions of these flex fans....so called race flex fans designed for very high rpm stuff and then a lower rpm rated fan that is of a little different design (based on my memory) back in my hot rod days.

I'm not a flex fan "fan"...others may like them...I do not. GM has been running the fan clutch and matching fan on their stuff for a long time...as have most other MFG who are still in the rear wheel drive game....none go with a flex fan...to the extent I know.

 

[Elbert]

The truck did run normal... Oddly enough with the smoking, crappy build 305 with a detonated piston it had in it when I bought it. It had a metal fixed blade fan on it (which I've also run on this set up to no avail). I would try a clutch fan, but my whole pulley setup is based on a long waterp ump, and it doesn't appear that there is enough room to not hit the radiator under torque. Also, if you'll note, it's overheating on the highway, not at idle or in town which seems like less of a fan issue to me since at 70-80 mph it should move ample air on its own (I obviously don't know though). That's why I mentioned timing, a/f and exhaust since those seemed most likely to cause overheating at speed, but all seem well based on how well it runs/starts.

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agree... timing could be an issue with overheating and generally overheating at speed is an issue with a defective radiator.... My truck runs hotter at constant sustained speed than not (in my case I'm pushing up some RPMS do to low gears (4.88).

Forgot if you said it was a carb engine or not, but if so you need to check the timing and advance if so, regardless if its easy to start. I had a defective HEI distributor one time that caused overheating on old school 5.7 carb setup.

I follow you on the accessory drive business... my fan is very close to the radiator core...but it works.

You'll see some threads here about electric fans and all of that... I and some others think the fan clutch setup is the way to go. If the condition is at speed only...then it may not be the flex fan as I initially suggested but I'm still of the view that the RPM range of the flex style fan for engagement is too narrow. But thats my view.

If you are fuel injected then I assume your base timing is good and no check engine light on, no codes set?

Sounds like you have checked for obvious radiator blockage and condensor blockage.

Pics always help these type of questions.... if you want to see my setup I can post up too.

If you are old school setup I like the V belt fan (7 blade type) but it too is a fan clutch setup (GM).

 

[Mace]

Overheating at speed is a result of not having enough cooling capacity. At 60 mph, your fan does pretty much nothing..

Your aftermarket aluminum radiator should do the trick.

BTW, flex fans are designed to flatten out with engine RPM. They are designed this way to reduce the parasitic drag on the motor. They pull more air at lower engine RPM's.

 

[Toadhopper]

I have pretty much the same issue going on (TBI 350 with a stock rad.) Same issue at freeway speeds, except I dont have the AC hooked up yet. I'm sure if I did it'd be heating right up to the range you're talking about.
I'm going back to the OEM water pump fan and fan clutch.
Making sure the shroud doesnt occlude any surface area is key. My water pump is high volume, but I'm thinking with a 5.7L motor, and the water moving 30% faster through a rad thats smaller than the engine was designed for it might not be giving the water enough time to cool given the rads surface area (not sure if your pump is hi vol).
Let us know how the alum rad works out, but remember to take care of all the other things that might be contributing to the issue since the new rad might just be masking the orig issue.

 

[doug720]

Years ago I helped a buddy with a V8 swap into Triumph sports car. He also had cooling issues and went through the same checks and ideas, all to no avail.

After many ideas and discussions with anyone who would listen, the radiator shop owner asked if the radiator was a cross flow, bottom flow of top flow model? He did not know!

It turns out he had a top flow and what he needed was was a bottom inlet cross flow radiator. The problem was how fast the coolant was flowing through the radiator. In this case too fast to allow the water to transfer the heat to the air flow.

The radiator shop built him a bottom inlet cross flow with 4 rows that fit perfect. He changed the radiator and lived/drove happily ever after. No more heating issues.

Will this fix yours, I don't know, but maybe worth a look? You have a good engine, new thermostat, good water pump, clean radiator, good coolant flow, no codes and it gets hot while moving fast. Unless something is blocking the air flow, it's going to be something weird like I suggested

Doug

 

[snobdds]

Years ago I helped a buddy with a V8 swap into Triumph sports car. He also had cooling issues and went through the same checks and ideas, all to no avail.

After many ideas and discussions with anyone who would listen, the radiator shop owner asked if the radiator was a cross flow, bottom flow of top flow model? He did not know!

It turns out he had a top flow and what he needed was was a bottom inlet cross flow radiator. The problem was how fast the coolant was flowing through the radiator. In this case too fast to allow the water to transfer the heat to the air flow.

The radiator shop built him a bottom inlet cross flow with 4 rows that fit perfect. He changed the radiator and lived/drove happily ever after. No more heating issues.

Will this fix yours, I don't know, but maybe worth a look? You have a good engine, new thermostat, good water pump, clean radiator, good coolant flow, no codes and it gets hot while moving fast. Unless something is blocking the air flow, it's going to be something weird like I suggested

Doug

I also believe the coolant is not staying in the radiator long enough to be cooled properly.

 

[workingdog]

I have to agree with Mace and Snobdds, it's not an air flow issue on the freeway.

It has to be either
1. The coolant is not losing enough heat in the radiator (either flow or capacity).
2. The coolant system is not holding pressure.
3. There is trapped air.

You've said you checked #3. Have you checked #2. Is this a CARB setup with a separate bottle? Do both the radiator and bottle have cap? Are they working?

Peter

 

[Elbert]

Just some info....while I was surfing around yesterday I noticed that Griffin radiator has a direct fit aluminum radiator for the 60, the other options are the ron davis one you can get through MAF and I think AA is selling one too, but I don't know who makes it.

http://www.griffinrad.com/offroad/radiators.cfm

I don't know anything about Griffin but there is a good write up on them over on Pirate in the technical section... Just throwing this out there as another source. There may be others but these are the ones I know about.

 

[coop77]

Just some info....while I was surfing around yesterday I noticed that Griffin radiator has a direct fit aluminum radiator for the 60, the other options are the ron davis one you can get through MAF and I think AA is selling one too, but I don't know who makes it.

http://www.griffinrad.com/offroad/radiators.cfm

I don't know anything about Griffin but there is a good write up on them over on Pirate in the technical section... Just throwing this out there as another source. There may be others but these are the ones I know about.

So, I drove up to the mechanics shop to discuss a plan, and he wants to cut the interior of the fenders slightly, refab the battery trays over further in each direction, and put a two pass cross-flow radiator in there. If this doesn't do it, it will definitely overheat as it burns tot the ground!

BTW just in case someone else is searching it later, I have run this with an Edelbrock 650 and the FAST EZ EFI set-up (which I will go back to if I get it running right).

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[Elbert]

A bigger radiator would be a plus as long as you had good air flow and shroud to match. I would love to have a radiator out of a 3/4 ton GM truck in the 60...but have not yet decided to start chopping things up to get there.

I don't know why Toyota uses the radiator design with the tanks top and bottom (it may be a space issue).

 

[Toadhopper]

So, I drove up to the mechanics shop to discuss a plan, and he wants to cut the interior of the fenders slightly, refab the battery trays over further in each direction, and put a two pass cross-flow radiator in there. If this doesn't do it, it will definitely overheat as it burns tot the ground!

BTW just in case someone else is searching it later, I have run this with an Edelbrock 650 and the FAST EZ EFI set-up (which I will go back to if I get it running right).

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If you end up going that route, take some pics and post up which rad he decided to go with. I hate cutting....especially if the area doesn't have adequate airflow. You can make a really big hole, but of there isn't air blowing through it I cant see the point.

 

[M1A1cruiser]

I note you said battery TRAYS so perhaps you've got dual batteries so there might be a crux.

But I can tell ya' that a new (I went with Griffin, but there are many out there) radiator will fit between the fenders. You can get probably total width of 27" in there without cutting and just moving some stuff around, build some custom mounts, etc.

I know that lots of swaps have been done using the original radiator (or original gas tank, A/C compressor, whatever else...) but if you're going to a new radiator anyway call a couple of the outfitters and talk to them about your measurements, whether you want to stay mechanical fan or not (that's a whole other thread), etc and they can build something that will fit exactly what you want and presumably cool better than the 20+ year old stuff we all have now - or started with.

Just sayin', it's at least worth a phone call to Griffin or Be Cool or whomever.

TDC.-

 

[ntsqd]

The cross-flow from a '92 Camaro Z-28 won't require butchering the core support and it's fin area is almost a perfect match for the existing opening in the core support. I had one built 3 core with a high fin density. Truck doesn't run yet, so I can't comment on how well it works.

I don't buy the coolant too fast thru the radiator explanation. Water gains and loses heat too fast for that, there was some other reason that slowing down the coolant fixed the problem.

New pump means nothing. Buy a new QUALITY pump, like one from Stewart Racing Components. I once had a car that had a new pump on it (recently installed by the PO) that would over-heat under any load but never driving around on the streets or on the fwy. Not even when hot-dogging it would it over-heat, but hook up a small trailer and it would. After much changing stuff and fiddling around the only thing left was the pump, so I replaced it with a Stewart part. Then I had to undo some of the mods that I'd made trying to keep it cool in order for it to warm up!

I'm also a non-believer in aluminum radiators. Sure are pretty, but they are not better at exchanging heat than copper-brass, they just weigh less.