71 350 running hot coolant backup up problem

[Gregski]

Originally Posted by Gromit

I did notice the 850 RPM idle speed you mentioned sounded about 200 RPMs high but since some people like what I would consider a high idle so I didn't want to judge.. I prefer a putta-put-put - maximum 650 RPM or as low as I can get it to run smoothly in that neighborhood.

I did test your theory, I used to have a Harley so I like the Potato Potato low idle rumble too! lol So I tested at 700 RPM idle which yielded a 500 RPM while stopped in Drive or in Reverse. Truck did not like that real low 500 RPM and would shake and hesitate and really struggle idling smoothly. Also there was no change in the overheating, again it was fine in Park/Neutral and temps started climbing in Drive/Reverse with my foot on the brake. So I had to pump the RPM at idle back to 800 where it is happiest, but it was worth a try.

Originally Posted by Gromit

You definitely don't want your centrifugal advance coming in at whatever idle you wanna use.

I wonder if you are on to something. The idle timing with manifold vacuum is 35* (13.5 initial + 14 vacuum? + 7.5 centrifugal?) that would mean I may need to adjust my ignition curve as the mechanical is coming in too early. I don't recall what color springs I am running on this Accel HEI distributor, may be time to check. My vacuum canister is adjustable so I may be able to take some advance out that way too.

Here is a brilliant article by Jeff Smith: Understanding Vacuum Advance and Why You Need It

Originally Posted by Gromit

Hey I may have been wrong about your initial timing being the cause of your overheating...

Hey, don't count yourself out just yet brother, I know for a fact timing was the initial culprit. Remember when I discovered I had a bad vacuum advance canister, well, replacing that can fixed my overheating problem at idle, ie in Park/Neutral, since the truck likes Manifold Vacuum, ie lots of advance at idle

[Gregski]

Here is a rather interesting RPM Test:

I went for a cruise then I pulled into a parking lot and I simulated a traffic stop say at a stop sign or a red light, cause that's when the temp climbs. So I left the truck in Drive and just stood on the brake.

After 2 minutes it went from 175ish to 190* and kept climbing for 5 minutes. This was at 600 RPM. Disclaimer I know 190* is not hot, I get it, but in the past it would shoot over 200*, so tonight may have been colder out etc... I doubt simply hooking up a Tach fixed my overheating problem, LOL.

Then I decided to just put the truck in Park and see what happens. The temp immediately started to drop, in two minutes it was down to 180* then after five minutes dropped to 175*. This was at 800 RPM

So I thought to myself... self: what if I increase my idle speed therefor increasing the in gear RPMs. Well I had to creep up the idle RPMs to 1000 in order to get the in Drive or Reverse RPMs to 700 and at those settings the truck ran hot just like it did at 600 RPM. Just sharing that tid bit.

[Gregski]

The one thing I have not changed yet is the flex fan, so I am scratching my head on that. You would think that if it cools at 800 RPM it should cool at 600 RPM, from what I gather, a flex fan flattens out at higher RPMs when it is no longer needed (assuming the vehicle is moving at speed) not at lower RPMs, am I missing something?

[Stocker]

Originally Posted by Gregski

The one thing I have not changed yet is the flex fan, so I am scratching my head on that. You would think that if it cools at 800 RPM it should cool at 600 RPM, from what I gather, a flex fan flattens out at higher RPMs when it is no longer needed (assuming the vehicle is moving at speed) not at lower RPMs, am I missing something?

I posted the following back on page 3 of this thread and I stand by it. Flex fans are junk in my opinion. A proper clutch fan will pull more air when needed at idle than a flex fan is able to.

Originally Posted by Stocker

I would throw the flex fan as far as possible and get a proper heavy duty fan clutch with a good OEM-type 7-blade fan bolted to it. That's what came on my K20 with a 350 and factory A/C. In 41 years, the only time it ran hot was when a clutch unit failed and I tried a flex fan. Didn't take me long to get rid of it and put the right one back on.

Just my 2 cents...

[stsalvage]

I'm not one for flex fans.Give me a 7 blade ford dodge or GM fan any day.Thats only when i running a fan clutch.If i'm not.Give me that old 4 blade fan.

The GM extreme Heavy duty for the 1975-77 454 engine.I had to put one on my 3/4 ton It use to get hot sitting in a drive thru.It still gets hot.

My good friend I went to see him pulled up in his drive way smelled something burning.So i pup the hood.We looked to see if something was wrong He grabbed the top radiator hose it was Rock Hard.

I have one of there pressure re leaver caps on the radiator It was blowing air in to my catch can.The hose got lose.

He had me fire up the engine again with in 30 sec my top hose was Rock hard.

Means i have a cracked block cracked head or i have a crack in my head gasket.So i would check to see if you have a cracked anything cus your engine in pushing compression into your Motor.That will keep your water pump from wanting to turn or let your thirmistate from opening at all


This in the Number one reason whay you always run a heater core in your trucks Always.

If your truck ever starts heating up turn on the heater don't care if its 120 out side you fry or the truck fry's.Then you still FRY.

A working heater makes your truck work so much better.If you ever want to put in a manual chock and its 30 degrees out side and you want to let your truck warm up turn on the heater You will love your truck more.Do it right and it will give you lasting service.

[Gregski]

Originally Posted by stsalvage

Means i have a cracked block cracked head or i have a crack in my head gasket.So i would check to see if you have a cracked anything cus your engine in pushing compression into your Motor.That will keep your water pump from wanting to turn or let your thirmistate from opening at all

I doubt I have a cracked anything since it runs fine when parked or driving, it only heats up at a red light. When the head gasket busted on my mamas Cavalier it just kept getting hotter and hotter and hotter never healed itself like mine does at speed or in Park or in Neutral. Also I am not running low on coolant, nor is the engine oil like a milk shake, nor is there white smoke out the tailpipe.

I appreciate the feedback non the less, I am also learning a ton myself at this point and I am glad I have another vehicle to drive while I [ahem] WE figure it out, LOL

[Gregski]

Originally Posted by Stocker

I posted the following back on page 3 of this thread and I stand by it. Flex fans are junk in my opinion. A proper clutch fan will pull more air when needed at idle than a flex fan is able to.

I hear you, not sure if I posted this already, but a clutch fan was my Plan A, but the seven blade one I pulled off of a square body at the local Pick 'N' Pull did not fit inside my shroud, see pic below.

[Stocker]

Originally Posted by Gregski

I hear you, not sure if I posted this already, but a clutch fan was my Plan A, but the seven blade one I pulled off of a square body at the local Pick 'N' Pull did not fit inside my shroud, see pic below.

Measure your shroud.... shouldn't be any problem to find a 7-blade fan that fits. Not sure if I would trust a used clutch unit though... new ones are not expensive. If you get one, be sure to buy a heavy duty clutch, not a standard. HD can be identified by finned aluminum faceplate and thermal spring on the front. Standard has a smooth faceplate.
Good info here: http://www.haydenauto.com/featured%2...s/content.aspx

[Boog]

Doesn't the big block engines use larger diameter blades? That looks like one.

[Keystone_Hate]

Man it sounds like you've got it pretty narrowed down. Airflow!

[Gregski]

and a little stare and compare of the two 18" fans, the mechanical? and the flex fan

full frontal and backside

[Gregski]

so Test Results with the conventional four blade fan.

In a nutshell, no change, no difference than with the flex fan.

Cruising around the wind blows at the front of the truck so with either fan the temp gauge reads in the mid 175*s, but that's to be expected as the air overcomes the fans ability, I just wanted to level set

Now, in Park or in Neutral the truck is fine it will idle at 800 RPM in the low 180*s F, same with both type of fans

And in Drive or in Reverse with my foot on the brake (the RPMs drop to 600) the temp starts climbing, it will reach mid 195*s in five minutes and slowly keep creeping up above 200* eventually (about ten minutes later) again same with both fans

So I shift back to Park and watch the temps immediately start to drop, the gauge will return back down to the mid 185* or so, again same with both types of fans

just wanted to report that

[Gregski]

this is by far the best ignition timing and vacuum advance write up out here on the Internets so I am cut and pasting it into this thread, of course giving credit and a ton of thanks to the brilliant and gracious author Vacuum Advance- how is it supposed to work? complements of ChevyTalk.org

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

Bill -
55 Chevy 210 2 Door Sedan Hot Rod
http://imgur.com/a/CfOc6
68 Caddy Coupe DeVille Kustom
http://imgur.com/a/m7gdR

[toolboxchev]

I went through my distributor after reading this one:

http://www.crankshaftcoalition.com/w...EI_distributor

Its all about controlling the burn!

Your carb may also have something to do with it. Systems all need to work together to achieve maximum efficiency.

[Gregski]

Originally Posted by CaptRMW

With your 195 degree thermostat you just added 15 degrees to the normal operating temp of your engine. 180 degree thermostat was original.

Where are you getting this information from? When I do a search for an OE replacement thermostat for a 1971 truck on AutoZone I get 195 degrees, I do the same for my 1974 and get the same result, I do it again for the latest 1986 square body and still get 195 as the direct replacement.

[OBS454]

Originally Posted by Gregski

Where are you getting this information from? When I do a search for an OE replacement thermostat for a 1971 truck on AutoZone I get 195 degrees, I do the same for my 1974 and get the same result, I do it again for the latest 1986 square body and still get 195 as the direct replacement.

The 195 degree thermostats came about when ECM engines came out. The most common thermostat in V8 engines up till the early 80s was the 180 degree thermostat. I was also in auto repair starting in 1981 so I changed a lot of them. It's possible the 195 you have in there is not working properly. Get a quality 180 and install that. Check your engine timing - retarded can cause overheating to some degree. Move your hand around different areas of the radiator to check for cool spots - a partially clogged radiator core is possible. Feel the upper and lower hoses for temperature differences. If you grasp the upper hose after the thermostat has opened (use a rag or something to prevent burning) you can actually feel the water passing through as it scrubs against the inside of the hose. Check to see if the fan is pulling air - is it the correct rotation? Water pumps that are intended for serpentine systems (like my 1990) have pump impellers that are designed to work in a counter-clockwise rotation (and so is the radiator fan). Perhaps the wrong pump was installed.

[rockyrivermark]

I would double check those temps with an IR gun
They are pretty cheap and nice to have around.
Shoot right at the T stat housing.

[dozerbill72]

Did the engine sit around with the intake or thermostat housing off? I had a bunch of engines in a shed become apartment complexes for mice. Like to never get all the nests out of the water jackets. A nest sure would cause a flow problem. I would think you should have found some junk in the thermostat as many times as you have had it out, but just a thought.

[Larry Weaver]

Fry a dif temp gauge ??

[Andy4639]

According to auto zone both of them are OE recommended. 180-195.

I would think it depends on if you have the 307 are the 350 just guessing here. Either one should work just fine though.
I have to agree with the other's. I would be taking the radiator out and have it rodded out are buy a new one.

[B Myers]

If it's in my shop I drain the system and run a scope down the radiator filler cap and look at the cores for blockage, it there is replace or recore the radiator. It needs a fan shroud with a good clutch, 195 degree tstat that is new, fill with proper mix coolant, run till its flowing and install the cap to pressurize. Using the digital thermometer you can scan the tstat housing for temp and it should run around 200. You can scan areas on the radiator for heat, it should be even, if it has cold spots then its plugged. That should get you fixed. If that's not it then it is not good, pulling water pump and looking for blockage in the block or heads assuming your thermometer is accurate. It is normal to have some coolant loss from the overflow hose due to fluid expansion by the way. If it gets hot and is not boiling over and just running in the 200 range its ok.

[demian5]

Originally Posted by rockyrivermark

I would double check those temps with an IR gun
They are pretty cheap and nice to have around.
Shoot right at the T stat housing.

I was looking through the thread and don't see where you got an IR temp gun and confirmed that the engine is actually this hot?