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68 Cooling & Fan Shroud HELP!

69396Chevy

Member
Joined
Apr 11, 2005
Messages
14
Location
Michigan
Hi all . . OK hopefully someone can help me out. My 68 with a 350 I just purchased recently is having cooling problems. Up here in MI this past weekend it was pretty humid and hot, took the car out to have a paint match done on it in normal driving and it goes up to 210, maybe slightly higher. I put a new 160 stat in it along with a new cap, the cap was junk and wouldnt hold any pressure. I still get the same thing letting the car run in the gargage and the upper hose always stays hard like the stat isnt opening. I added about 1/2 - 3/4 of a gallon of antifreeze and it didnt seem to help. The gauge sending unit is in the head which I want to move and put next to the stat where it should be for a more accurate reading. Also my fan shroud seems really short, the clutch on the front of the fan isnt even in the shroud. When I purchased the car the owner said when he bought it he thought it was a BB car but he realized it wasnt after some research so Im wondering if its a BB shroud since the fan is so far away from the rad. I have receipts showing he had the rad cleaned pressure checked and all that kind of stuff and he said it was a BB rad, since this is my first vette I cant say for sure if it is or not. A couple weeks ago me and the Mrs had it out for an 80 mile sunday roundtrip ride and since it wasnt near as hot out the car ran about 170-180, but if I recall I think I had the heat on medium cause the Mrs was a little chilled. So my questions are this:

What temp should this car be running at with a 350 in it?

Do I have the correct shroud? Will gladly send a pic to anyone who wants to see the setup so they can see for themself what Ive got . . . cant figure out how to load pics.

Can having the gauge sending unit in the head be reading a temp thats really far off what it actually is? Just a reach here but since the upper hose seems to stay hard maybe the temp is reading so far off of what the actual temp is that the stat hasnt opened yet . . . like I said just a reach and wishful thinking.

Need some help guys!! Thanks in advance!
Chris

Whats the norm to do for hot running vettes, was thinking of putting either electric fans or a new aluminum radiator
 

randomize27

Member
Joined
Jun 9, 2005
Messages
15
Location
Columbia, Missouri
Corvette
Wal Mart Remote Control C6 - Daily Driver
When I was having some radiator/coolant trouble a couple years ago, my master-mechanic father helped me troubleshoot it. (But, it wasn't a Corvette, so you may wish to take this advice with anything from a grain of salt to a salt lick.)

You've started off right - Check the thermostat first. Easiest and cheapest repair. If you run the Corvette for anywhere from 5 to 7 minutes, and there's not a drop in RPM's, then the thermostat is not opening for some reason. (Of course, grabbing the top hose works too, but is not always reliable. The engine is working harder to keep the pressure up until the thermostat opens, so the RPMs will drop, but sometimes, the car's upper radiator hose stays hard [from potato hard to apple hard would be a good comparison, you can squeeze an apple just a little, but you can't really squeeze a ripe potato.) constantly, thus it's not always a good check.) Another way to check this, is to remove the thermostat for a few minutes. But, above all, DO NOT DRIVE WITH THE THERMOSTAT REMOVED. Run it for 5-10 minutes at most - the temp gauge should show it running cool, and the upper hose should be soft. If the upper hose is not soft with the thermostat removed, there is a blockage in the coolant system somewhere.

(I didn't have a blockage, so don't know how to deal with it.)

Now, another thing to check is the pressure. My dad has gauges and adaptors to do this, but since I didn't, he told me to disconnect the upper radiator hose from the thermostat housing, and direct it into a 1 gallon bucket. Have someone else start the car. If the bucket fills within 30 seconds, you have too much pressure from the water pump. If it fills within a minute to a minute and a half, then the pressure is about right. If it takes longer, you're not getting enough pressure. (This was on a '91 Cutlass Supreme, so....check your salt.) (Also, you might want to use a 5 gallon bucket with a 1 gallon line - just in case of too much pressure.) (This is also a 2 person check.)

Now, I didn't have problem with the fan shrouds, because I had electric fans inside their own shrouds, but I think, logically, it'd be a good idea to make sure the shroud covers the fan. It could be that the fan is pulling air from around the outside of the shroud instead of pulling it through the shroud and radiator. But, getting OEM parts for an older 'Vette can be hideously expensive.

Again, this is all to be taken with various amounts of salt. I'm not an expert, and make no claims on how effective any of this advice is.
 
Joined
Aug 29, 2001
Messages
3,236
Location
Norcross, Georgia, United Stat
Corvette
2017 Arctic White Grand Sport
The fan should sit just in the opening for the shroud.

What kind of driving where you getting 210 on. Stop and go on a hot day? Freeway?

My car runs about 200 with the a/c on on the freeway on a 85 - 90 degree day. On the same day in traffic 220 or so is not impossible.

You may want to reconsider the 160 degree thermostat if you have any plans to run the car in cool weather. The thermostat sets the minimum temperature and doesn't have anything to do with the top end. If it runs to cold you won't get the condensate, etc out of the oil.

JohnZ said:
The heat-shield underlayment is quite effective - good idea to install it. A 160 thermostat won't make your engine run any cooler (except possibly in the dead of winter) - thermostats control MINIMUM temperature, not maximum operating temperature - that's controlled by the capacity of your radiator. 160 is too cold anyway - it won't let your oil get hot enough to boil off condensed moisture and blow-by contaminants, and acidic sludge will form faster.
 

69396Chevy

Member
Joined
Apr 11, 2005
Messages
14
Location
Michigan
Sorry Bob forgot to answer your questions . . . it was mostly go . . . not alot of stopping. It was very hot and humid though, had to have been near 90. I replaced a 69 396 Chevelle with this vette and I had a 2 core (2 cores but each was 1 inch wide) aluminum rad for it and it never got above 170-180 in normal driving, stop and go it would get to maybe 190 then come down as soon as we started moving. Maybe Im just paranoid since this seems alot higher than Im use to and this is my first Vette BUT the engine has no clue what sort of car its in so the principles of how hot they should run should be the same.
 
Joined
Aug 29, 2001
Messages
3,236
Location
Norcross, Georgia, United Stat
Corvette
2017 Arctic White Grand Sport
Assuming a good radiator and fan, the diagnosis is different depending on when you get your heat. If it gets hot moving, you start looking at the chin scoop and seals which direct air through the radiator rather than allowing it to go around it. If the radiator was out of the car for this work, I would start looking at these two items.
 

wallyknoch

Well-known member
Joined
Nov 9, 2002
Messages
457
Location
Dearborn
Corvette
One owner unrestored Black 1962 FI Corvette
Get that 160 degree stat out of the engine! You must use a minumum 180 and possibly a 195 in extreme hot weather. If I can recall, i`m using a 195 with my 68 L88 with a completely factory stock cooling system setup.
 

69396Chevy

Member
Joined
Apr 11, 2005
Messages
14
Location
Michigan
So what is normal operating temp and max operating temp? Maybe Im just paranoid but Im just not use to having a car that runs this hot . . .
 
Joined
Aug 29, 2001
Messages
3,236
Location
Norcross, Georgia, United Stat
Corvette
2017 Arctic White Grand Sport
Normal is hard to say. Different cars, even the same model years, run at different temps. I wouldn't worry about 210 but would look at the seals, fan clutch, etc., just to make sure it is not a warning that problems are developing.

I just picked up on the fact that your prior car had an aluminum radiator. The consensus seems to be that they cool a better more so to design rather than temperature characteristics.
 
G

goertz

Guest
all the termostat does is control WHEN coolant flows from the engine to the radiator. changing the t stat will make no difference if you have other issues with the cooling system. different temp stats do not allow different amounts of coolant pass into the radiator, it only controls the temperature that it opens. installing a 160 degree t stat only means that at 160 degrees, water starts flowing through the radiator. it doesn't by any means indicate your car will run at 160. in regards to a previous post, the engine doesn't work any harder pumping water through it when it's cold, and this is not a fuel injected car, so idle will not drop when it opens. removing the stat will most likely result in overheating, as the t stat also restricts the waterflow through the radiator, slowing it down, and giving it sufficient time to cool. if the water moves too fast through the radiator, as it will with no t stat, it will not cool. running a 195 t stat in your car is pointless, regardless of the weather. just run the 180 it should have. it sounds as though you have a few issues, i would guess the fan shroud is one of them. the fan should be INSIDE the shroud, or it won't work on a Vette, due to the angle of the radiator. As someone else noted, make sure all seals and air dams are in the proper location, and functioning well. this is important, as in these cars it's hard for the radiator to get air. if you run A/C and it's hot outside 210 is no problem at all. at 220, start to worry. if none of this helps, your problem is probably in the radiator, and a new aluminum radiator will probably cure all your problems. you can get them with electric fans, or get the correct fan shroud for your car. i'd bet the problem is the shroud.
 
G

goertz

Guest
randomize27 said:
When I was having some radiator/coolant trouble a couple years ago, my master-mechanic father helped me troubleshoot it. (But, it wasn't a Corvette, so you may wish to take this advice with anything from a grain of salt to a salt lick.)

You've started off right - Check the thermostat first. Easiest and cheapest repair. If you run the Corvette for anywhere from 5 to 7 minutes, and there's not a drop in RPM's, then the thermostat is not opening for some reason. (Of course, grabbing the top hose works too, but is not always reliable. The engine is working harder to keep the pressure up until the thermostat opens, so the RPMs will drop, but sometimes, the car's upper radiator hose stays hard [from potato hard to apple hard would be a good comparison, you can squeeze an apple just a little, but you can't really squeeze a ripe potato.) constantly, thus it's not always a good check.) Another way to check this, is to remove the thermostat for a few minutes. But, above all, DO NOT DRIVE WITH THE THERMOSTAT REMOVED. Run it for 5-10 minutes at most - the temp gauge should show it running cool, and the upper hose should be soft. If the upper hose is not soft with the thermostat removed, there is a blockage in the coolant system somewhere.

(I didn't have a blockage, so don't know how to deal with it.)

Now, another thing to check is the pressure. My dad has gauges and adaptors to do this, but since I didn't, he told me to disconnect the upper radiator hose from the thermostat housing, and direct it into a 1 gallon bucket. Have someone else start the car. If the bucket fills within 30 seconds, you have too much pressure from the water pump. If it fills within a minute to a minute and a half, then the pressure is about right. If it takes longer, you're not getting enough pressure. (This was on a '91 Cutlass Supreme, so....check your salt.) (Also, you might want to use a 5 gallon bucket with a 1 gallon line - just in case of too much pressure.) (This is also a 2 person check.)

Now, I didn't have problem with the fan shrouds, because I had electric fans inside their own shrouds, but I think, logically, it'd be a good idea to make sure the shroud covers the fan. It could be that the fan is pulling air from around the outside of the shroud instead of pulling it through the shroud and radiator. But, getting OEM parts for an older 'Vette can be hideously expensive.

Again, this is all to be taken with various amounts of salt. I'm not an expert, and make no claims on how effective any of this advice is.

there is no such thing as too much pressure, or not enough pressure from a waterpump. it either pumps, or it doesn't pump. no in betweens. they don't wear out, there is no pressure regulator. they either work fine, or they leak, that's it. a leaking pump will still pump the same amount of water as it did when it was new, it just makes a mess. in regards to rpm drop when t stat opens, that is correct, but only on a fuel injected engine, computer controls recognize engine has achieved operating temperatures, and it does into closed loop operation. these cars are carbureted, and the idle will drop when the choke comes off.
 

69396Chevy

Member
Joined
Apr 11, 2005
Messages
14
Location
Michigan
Going to put a 180 stat in it and get a spacer for the fan to get it inside the shroud if I can, if not then I'll have to see how much the shroud extensions are that I hear people post about. The guy who built the car was very meticulous and Im sure all the seals are there, I know I saw one below the rad that was sticking out some from the support when I looked at the car and thought wow he even replaced all this stuff . . at the time I thought the seals werent doing much of anything other than maybe helping rattles. I have a feelign though I'll end up with a new aluminum rad so I wont have to worry about it at all. First I gotta get the LT1 hood painted and installed but guess it would be best to do this all at once since the hood will be off huh!
 
G

goertz

Guest
i think you're on the right track. the entire fan doesn't have to be in the shroud, but it should be at least 1/2 way in there. this makes a HUGE difference. On my car, which is all original, (so I know this is how they came), when at idle, you open the hood, and put your hand in front of the condensor or radiator if no A/C, you can feel the draft of the air being drawn in. check that out on yours. if you can't feel anything there, i'd guess it's a shroud problem. Your temps aren't that horrible though. at least it's not a diesel, those are VERY particular to engine temps. I have a motorhome with a 6V-92 detroit diesel, and you have to watch that gage at all times. it needs to run at least 180, but at 200 you're in trouble, and at 210, the motor's finished, plan on spending about $10-15,000 for an overhaul. scary stuff.
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
Neither the thermostat (assuming it's working) nor the radiator cap have any effect on operating temperature; the thermostat only controls MINIMUM temperature, and the pressure cap only determines the temp at which the coolant will boil (and puke out through the overflow). Only two things control operating temperature (assuming no blockages or collapsing lower hoses) - the radiator's heat rejection capability, and the airflow through it to carry off the heat. Period.

If your shroud and seals are in place and the fan blade is half-in and half-out of the rear edge of the shroud and the fan clutch is working, that package handles the idle and low-speed traffic airflow issues. Your vacuum advance also must be operational and connected to full manifold vacuum (not "ported" vacuum) in order to have plenty of idle advance for adequate idle cooling; inoperative vacuum advance is a MAJOR contributor to running hot at idle and in slow traffic.

On the highway, the shroud and fan aren't that important; what matters is airflow through the radiator, which (on a C3) is a function of the front lower air dam; C3's are "bottom-breathers", and if the dam is damaged or missing, you'll lose nearly half the airflow through the radiator. If it cools OK in town and heats up on the highway, the problem is either inadequate airflow, or a radiator that simply can't cope with the heat input due to age, corrosion, and scale forming in the tubes.

Step #1 is to determine if you really have a problem at all. Shoot the upper radiator hose just above the thermostat housing with an I.R. gun and check the temp gauge reading at the same time so you know what the gauge is really telling you. Most Corvette temp gauges read 10-20 degrees high, especially if the original temp sender has been replaced. It makes no difference whether the sender is in the head or in the intake.

Forget the "whizbang" water pump debates, the "miracle water-wetter" debates, and all the gobbledygook theoretical discussions about coolant speed (too fast or too slow), thermal heat transfer theories, out-engineering the engineers who developed the cooling system, and all the Jeg's/Summit catalog hype about hot-rod cooling components. It's all about airflow, the radiator's heat rejection capability, and ignition timing.

:beer
 

Space Cowboy

Well-known member
Joined
Oct 8, 2003
Messages
408
Location
Houston Texas
Corvette
1968 Convertible - Candy Apple - 427/475+
When I bought my 68, I had cooling problems as well. It used to have a 427BB, but somewhere down the line it was replaced with a 350SB. The car now has a 427 back in it, but I decided to do away with the clutch fan and go electric from BeCool because of the poor design of the cooling system. I would check one thing for sure being that you have a 350... Do you have the shroud extension? If I remember correctly, the 350 sits further back from the radiator, and the shroud extension is MUST. Another thing to check is your water flow in the radiator with it opens up. I ended up scrapping my radiator and going with an aluminum BeCool because of some definite blockage. Also, you've probably done this already, but check your air cowling under the front bumper. Make sure its in tact. 180 degrees should be sufficient to run at.

Best of luck!
 
G

goertz

Guest
I was looking over my car tonight, and I noticed the shroud extension people talk about. i assume BB cars don't use it, and SB cars do. if you don't have it, you're screwed. get one. with it on there, the fan is almost completely inside the shroud, and this will make a huge difference.
 

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