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#1 |
Registered User
Join Date: Apr 2014
Location: California
Posts: 945
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BBC temp creeps at idle; how did factory do it?
How'd these trucks stay cool from the factory with AC?
My factory 402 truck does not have AC from factory. I took it upon myself to find a 4 core brass radiator out of a GM vehicle, this rad is almost identical to the factory 4-core for these trucks. Radiator shop said it was in "fantastic condition", they were rather surprised. Didn't need any work. Thermostat is 180º I use a mechanical gauge with sender placed at thermo housing. Fan was upgraded to a giant 5-blade 20.5" metal fan out of a 1972 Buick riviera that had AC. Everything looks factory.(According to internet non-AC '72 Riviera's had a four blade fan). This fan fits in the factory shroud perfect, partially in/out, it's like they were made for eachother. I also grabbed a 7-blade steel fan from a guy who has these trucks all over his yard. Both fans have a nice pitch to the blades--these things were made to move air. After installing and testing both fans on near 100º days, they had similar results and one issue: They will NOT keep engine sustained at any temp at idle(7-800rpm). It always creeps up, haven't let it go too high because the creep is slow and it would take forever(good thing). If at a stand still I bump the gas pedal to 1500 rpm it cools right back down in less than a minute at that engine speed. After extended 3000rpm driving today(98º) I pulled over immediately and the engine was at 190º. I sat at idle for a solid 10 minutes and it crept up to 210. At this point I put it in granny gear and drove 5mph at 1500rpm, in a minute it was down to 190º and stayed there without issue. As for as I'm concerned this is simply an issue of lack of air movement through the radiator at idle. If my truck creeps 30º or more on a 98º day and it doesn't even have AC, how did these trucks with this engine and factory AC keep cool? Did GM just not expect anyone to sit at idle for extended periods? I see guys in work trucks sitting at idle with AC blasting for half an hour today, I can't imagine people didn't do this 50 years ago. I can't imagine GM simply "overlooked" sitting at idle with AC on like nobody does that. Did these trucks slowly overheat from the factory? |
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#2 |
Senior Member
![]() Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,696
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Re: BBC temp creeps at idle; how did factory do it?
My truck is close to stock with a 350 and I can idle it or drive it down the highway, winter or summer, and the temperature stays rock steady all the time. So I think if you have a working system it should idle fine.
You didn't mention, do you have a thermo fan clutch? Is the water pump old? Is the radiator cap new or the original old one that came with the used radiator? Is your distributor vacuum advance connected to manifold vacuum or ported vacuum? |
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#3 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,388
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Re: BBC temp creeps at idle; how did factory do it?
I went round and round with my truck running hot, something it has done since I met my wife 41 years ago, when it still belonged to her parents. Bigger fan, custom shroud (because the fan clutch is about 1/2" from the radiator, which is a different problem) severe duty fan clutch, blah blah blah. It wasn't until I put in a high flow thermostat that it was tamed. The AC compressor clutch shoe drags, so I have the belt off until I get that replaced. It doesn't creep up any more, and starts better hot- since it isn't hot enough to sear steak on the intake manifold, anymore. We'll see what happens when I get to that shoe and can run the AC again.
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#4 |
Registered User
Join Date: Apr 2014
Location: California
Posts: 945
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Re: BBC temp creeps at idle; how did factory do it?
Yes I have a Hayden 2747 HD fan clutch.
Water pump says Made in USA and is painted engine color, so I'd say it was replaced when they rebuilt the engine an "unknown long time ago."(what I was told) Rad cap was given to me, looks newer, nice condition 16 lbs Vacuum advance is hooked to bottom of carb, so Ported vacuum. I believe I reset timing to 10-12º BTDC Thanks for your input Steve.....although it sounds to me this running hot thing might be normal.... |
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#5 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,623
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Re: BBC temp creeps at idle; how did factory do it?
2747 is an excellent heavy duty fan clutch for most circumstances. In your case, though, you *might* benefit from a severe-duty unit.
Differences are explained here: https://www.haydenauto.com/en/produc...-types/thermal I am curious about your 5-blade 20.5" Riviera fan. Small-block trucks use an 18" fan. Mine is 7-blade and works well. I was thinking big-block trucks use a 19.5" fan. At any rate, since you have a 7-blade, if it fits your shroud, maybe it's worth trying that before considering a severe-duty fan clutch.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#6 |
Senior Member
![]() Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,696
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Re: BBC temp creeps at idle; how did factory do it?
You might try switching to manifold vacuum for the distributor and see if your engine runs cooler at idle. I've heard it makes a difference. Changing between ported and manifold vacuum affects idle speed, so you'll need to adjust your idle speed screw. And pull off the water pump and see if the impeller blades are rusted away would cost you just some time and a new gasket.
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#7 |
Registered User
Join Date: Apr 2009
Location: PNW
Posts: 553
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Re: BBC temp creeps at idle; how did factory do it?
210 isn't that big of a deal.
I don't know anyone that sits at idle for 10 minutes other than taxi drivers at the airport. Is your shroud sealed to the radiator? How far is the clutch from the rad? Have you run the fan w/o the clutch? |
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#8 | ||
Registered User
Join Date: Apr 2014
Location: California
Posts: 945
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Re: BBC temp creeps at idle; how did factory do it?
Quote:
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#9 |
Registered User
Join Date: Jul 2018
Location: Catskill Mountains,NY
Posts: 8,469
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Re: BBC temp creeps at idle; how did factory do it?
210 isn’t hot for a big block . Where is the probe installed? If it’s in the head and not on the manifold 210 is normal as the head temp will always be hotter than the rest of the water. My 496 with a mechanical sensor in the head will creep up past 210 to 215 range before the fans kick in . The fan sensor is in the radiator and is set to come on at 195 and off at 180 . So the actual water temp in the system is cooler than the small amount in the head .
Has your truck actually overheated?
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Mark 72 c20 custom camper Husky edition, 66 SS396 Chevelle 1964 Hawk, 63 Avanti,62 lark 1969 AMX , 1968 c20 stepside ,85 K20 1977 Suburban sold 68 anniversary. |
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#10 |
Registered User
Join Date: Dec 1999
Location: Austin, TX, USA
Posts: 7,717
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Re: BBC temp creeps at idle; how did factory do it?
djmlambert is on the right track. You can Google a search for Lars white paper on big block Corvette ignition timing and engine cooling.
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44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax |
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#11 |
Registered User
Join Date: Oct 2016
Location: Dallas Texas
Posts: 3,081
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Re: BBC temp creeps at idle; how did factory do it?
.
My 402 with the A/C running on a hot day will creep at idle to about 215-220. This with two 14" fans pulling tons of air through the rad and the condenser. As mentioned, confirm your timing then let the thing creep. I suspect it will stabilize at a temp around 200 with no A/C. If you add A/C that temp will be higher. Before I upgraded to electric fans, my fan was running straight off the pump, no clutch. I was afraid of the temps at idle and would often do as you; increase the RPM to cool it down. My rad is the old school 4 row. Hth, -klb
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67 C10 fleet fuel injected '70 402, 700r4, 3.73 posi 07 335 sport turbo 6sp 94 Trans Am GT LT1 6sp posi -- sold after 22yrs 99 540 sport V8 6sp -- sold 73 240z L24 4sp -- given to friend 68 C10 step 350/350 3.73 open -- sold |
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#12 | |
Registered User
Join Date: Apr 2014
Location: California
Posts: 945
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Re: BBC temp creeps at idle; how did factory do it?
Quote:
You make an interesting point about BBC temperatures, because when I decided to change radiators a few weeks ago I did LOTS of reading and there was about a million threads all over the internet saying two things: "Why does my BBC runs hot?", and "BBC's tend to run hot". ![]() No it has not actually overheated. Some of the threads had guys who regularly ran their engines at 220-230 and made no issue. My problem with all this is, I am expecting to make this truck a prolonged daily driver. I live in a hot climate, and expect to make many trips in deserts and mountains. What if there is some crazy traffic jam on my way to vegas in the summer and I'm left sitting still for 10-15+ minutes in 90-100º weather? I need to know this truck isn't gonna let me down. My modern car doesn't cry and moan when I sit still with AC--but that cars on it's way out the door, so this truck has to behave well for me to be able to rely on it. (maybe I'm the one crying and moaning and not my truck) |
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#13 | |
Registered User
Join Date: Apr 2009
Location: PNW
Posts: 553
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Re: BBC temp creeps at idle; how did factory do it?
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#14 |
Registered User
Join Date: Oct 2013
Location: Central Coast Ca.
Posts: 417
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Re: BBC temp creeps at idle; how did factory do it?
Get a new 4 core copper radiator! Run no more than 50:50 glycol/water and make sure the block is purged of all trapped air: run heater, burp hoses, etc.
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1971 SWB step side: Original NM Forestry and then NM Fire truck |
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#15 | |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,108
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Re: BBC temp creeps at idle; how did factory do it?
Quote:
I remember the family going to the casinos in town on 100 degree days just to walk around in a cool place. Or standing in the door of a grocery store freezer to cool off as the store's swamp cooler would only bring the store temperature down to 75 degrees when it was 90 or more outside. That grocery store was only 10 or 15,000 square feet. I find it amazing that today the same store is 150 to 200,000 square feet and perfectly climate controlled. Is my gray hair showing? ![]() When these trucks were designed in the mid-sixtys stop and go traffic wasn't really a problem and trucks were not used for commuting. So as far as GM was concerned if your big block stayed cool going down the road fully loaded they were happy.
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Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
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#16 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,623
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Re: BBC temp creeps at idle; how did factory do it?
As mentioned above, 210* is far from overheating. I understand your concern about it creeping up very far above 210* in extreme conditions, but keep in mind that at zero pressure, water boils at 212 and a 50/50 mix boils at 226.
Just 8 psi raises water's boiling point to 233 and 50/50 mix to 248.
__________________
- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#17 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,388
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Re: BBC temp creeps at idle; how did factory do it?
FWIW, my truck has gotten as hot as 260F pulling a 6000 pound travel trailer up a steep grade without blowing a head gasket, and this rebuild has 100k+ miles on it. It didn't make me happy to see that, but it survived.
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#18 |
Registered User
Join Date: Apr 2014
Location: California
Posts: 945
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Re: BBC temp creeps at idle; how did factory do it?
I supposedly have a modern aluminum 2 1" core coming, back ordered till the end of June, we'll see. I bought it first, then saw this original radiator at a junkyard and figured they aren't that common to see so I bought it.
Yes it is true that AC is more prevalent and used more willingly today. My coolant ratios are a bit mixed from removing the radiator a few times, so maybe that's an issue is well. Steve that's nuts that it got that hot, but its pretty fun knowing your ole truck can still do it. What temp was the truck running when you were cruising on flat ground on that trip, just for reference? Had it ever gotten hot like that before? |
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#19 |
Registered User
Join Date: Nov 2014
Location: Austin
Posts: 749
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Re: BBC temp creeps at idle; how did factory do it?
Just for informational purposes. As I mentioned, my sbc would creep way up in temp when sitting at idle, a/c on, in traffic. Start driving and temp would come down to about middle of gauge or slightly above. Then, took the truck off the road to do rust repair and paint. One year later, I put the truck back together with a new smaller (not heavy duty) 2 core aluminum radiator. Now, it seems my temp sender is broken. Temp gauge has never made it to half way. Stays in lower range of gauge and never goes above half way mark no mater the outside temp a/c on or off.
It was my old radiator causing my temp issues! |
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#20 |
Who Changed This?
![]() Join Date: Jan 2013
Location: Simi Valley, CA
Posts: 10,388
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Re: BBC temp creeps at idle; how did factory do it?
I don't really remember, I was just worried about the high temps.
I worked for Chevrolet dealers on and off in the early '70s. I remember the '71 SB400 engines, even in the big wagons with AC, were getting 2-row radiators. We had a bunch of them in the service department with toasted engines, getting retrofitted with bigger radiators. I don't remember if they simply replaced the engines or rebuilt them, but some of them were pretty crispy inside. So GM built some marginal cooling systems on occasion.
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~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA |
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#21 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: BBC temp creeps at idle; how did factory do it?
What a lot of people forget, is these trucks were brand new at one point. Almost nothing on them is "factory set". We tinker with carbs, change air hats and filters, eliminate emissions stuff, change timing, etc. I don't know what affects it would have, but was also don't even run the same types of fuels and oils as when these trucks were new. I believe the factory timing setting back when leaded fuel was used was 6-8* at idle. Now, if you run HEI and modern fuel it's closer to 10-12*.
And as mentioned above, 210* is fine. I had to learn and accept that. My truck has aftermarket A/C, 7 blade? clutch fan, and big 4 row. It runs about 195*-200 on a hot day if I have the air off. If will run 200-210 with the A/C on. At idle, it will cycle between 205-210. It will run 195-200 down the road. I think my T-stat is a 190. I've found it's better to run a hotter T-stat because in SC it's going to run that hot anyway. It's better to let the water have more time to cool in the radiator with a higher T-stat than to have it constantly running through the radiator trying to cool. My 2015 Z71's operating temp is 210*.
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#22 |
Senior Member
![]() Join Date: Jul 2000
Location: North Texas
Posts: 3,488
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Re: BBC temp creeps at idle; how did factory do it?
In your part of the country, I'd use 40/60 or even 30/70 (antifreeze/water). Water transfers heat better than antifreeze. Then check the chart to select a pressure cap with a boiling point above 230. I'd also consider a high-flow t-stat from Robertshaw or Flow Kooler. And if you don't have a recovery tank, get one.
But don't get caught up trying to keep the temp at 180 degrees. 190-200 is just fine, and does a better job of causing condensation in the crankcase to evaporate. One more thing: Some folks will say aftermarket aluminum radiators are junk. However, aluminum does a better job of transferring heat. On my square body, I bought a 2-row aluminum radiator from O'Reilly Auto with a lifetime warranty. Even through five Texas summers it kept my 350 in the 190 range, and no higher than 200 at a stop light. The truck did have a new AC Delco water pump and a clutch fan with shroud. There were two larger radiator sizes available, but I bought the smaller one after speaking to a guy who used it with a blown 383! And I already had brackets and shroud for the smaller one. My truck's water temp gauge was a decent quality Autometer electric, but one of their "full-sweep" mechanical gauges would give you better resolution. https://www.autometer.com/2-5-8-wate...80-f-mech.html ![]()
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Mike 1969 C10 LWB -- owned for 35 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- sold 1981 C10 Silverado LWB -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then! Last edited by MikeB; 06-18-2021 at 09:36 AM. |
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#23 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,623
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Re: BBC temp creeps at idle; how did factory do it?
Yes, absolutely. And if you get a recovery tank, you need a radiator cap for a sealed system so the coolant can be drawn back into the radiator as it cools.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#24 | |
Registered User
Join Date: Apr 2014
Location: California
Posts: 945
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Re: BBC temp creeps at idle; how did factory do it?
Quote:
Thanks for the replies, ya'll. This thread has really gone in depth and I appreciate it. |
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#25 |
Registered User
Join Date: Nov 2013
Location: Inman S.C.
Posts: 67
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Re: BBC temp creeps at idle; how did factory do it?
Has anyone tried adding an oil cooler with a thermostat controlled electric fan?
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