I had a chronic high temp problem with my '68 SB, so last year I installed an aluminum radiator and 160 deg thermostat. I completely sealed the radiator shroud with foam, but the rubber piece on the front edge of the fan shroud is now about 3/4" away from the rear surface of the radiator. With the original stock radiator in the car this piece was basically in contact with the fins. Should I un-staple and reposition this rubber piece so it is in contact with the rad, and will this have any effect on cooling?

I fired her up for the first time on Monday, and let her idle while I checked the fluids, etc. Pegged on 160 deg, but when I got out and opened her up on a straightaway, the temp started climbing right away. After a little more spirited driving I got stuck at a light and the temp went up to 250 deg. Got home quick and shut down. Put the laser thermometer on the upper hose and thermostat housing and they were reading 210 - 218 deg. Lost about a half cup of coolant out the overflow.

I've read conflicting advice about new/hi-flo water pumps; would one of these help with my situation? Also, I've had a flex fan on her since last year, but got a new clutch over the winter, which I will be installing soon.

I've got to get this overheating business under control...any advice would be appreciated. Thanks

Chris

 

The more air you can force through the radiator the better off you are. The air that is by passing the radiator is doing nothing for you. I'm not sure if this would actually cause as much over heating as you said happened. I would fix the air by pass issue but I would also look for some other issue that could have cause the over heating but there is something unusual going on.

You did not say what modifications if any you have done to the engine. The weather was a little on the cool side in Naperville last weekend so there is a chance you may be running a little lean which would cause excess heating.

 

Guessing you've got a 68, 4 speed, small block radiator, it's a really small rad, and the fan shroud is crappy. Seal everything, make sure you have the correct front air dam, bottom air seal, and rubber radiator support to hood seal in place. Also consider a radiator mounted electric fan actuated by a temp sensor. I added a $60 Advance Auto electric fan and it really helped.

 

I agree with the above post, install a electric fan but I would go with a dual and not a single. A friend of mine had a single and still had some minor cooling issues so he changed to a dual fan and it solved everything.. I too have a aluminum rad and single fan but still climb above 200 on a rare ocassion (certain angles of a road or hill) so I'll be switching to a dual soon.. My friend went with this fan, which he says is much quieter than his single fan was.


FD

 

Just to be clear, will the car sit and idle at 160 indefinitely? Does it only heat up when you're drivng? Typically if it heats up while you're sitting its an air flow problem. If it heats up while you're moving its a coolent flow issue. You may also have a leaking head gasket, or a timing advance issue.

 

It idled at 160 deg for at least 20 minutes while I topped off ATF, steering, tire press etc. Then down the hill, around the corner (maybe 3/4 mile?) and stomped it up to about 50mph. I looked down and it was up to 200 deg. A little more fast driving and it was +/- 230 deg, then I got stuck at two lights and it crept up to 250 deg while I was idling.

Thanks to all for the responses so far...beginning to wonder if a new H2O pump might be worth a try...?

 

check the timing

 

Two easy questions, is your thermostat opening and is your temp gauge working? I always check the most basic things first.

 

It's a 68, manual, 4 speed folks...have any of you seen the size of the radiator, or how crappy the fan shroud is? And he's running a flex fan....
Sure, check your timing, you should do that anyway. But if your water pump isn't leaking, it's fine.
Seal it up, buy an electric fan, relay, and temp switch.
Oh yeah, the temp guage/sender on mine tends to read high, confirmed by IR gun and an additional gauge.

 

fan shroud should be against the radiator,

Fan is not pulling air through the radiator but around the shroud

this should take care of the idle issue and possibly help with the spirited driving temp issue.

pull the 160* and go with a 180* or 195*, this wont make any change to the high temp issues until you find and resolve the problem but it will set the max temp once you find your problem and regain your cooling capacity/efficiency.

make sure all radiator seals are in place

Neal

 

That engine & cooling system probably went to 200F idling for 20 minutes when it was new. Putting a lower temperature thermostat won't keep temps at 160F; it will only guarantee that the engine temperature will get up to 160F pretty quickly. The cooling system design and condition will determine where the temperature stabilizes.

200F presents no concern at all to your engine. Up to 230F with a pressurized cooling system and a 50/50 mix of water/coolant will not allow that to boil or damage the engine, and the dyno oil is good up to 240F or so. If you use synthetic oil, you will boil off the coolant before that stuff will have a problem with temperature.

 

might want to check mixture-timing. two easy things to look into before ya go deeper?

 

For 37 years, now, every spring when I get out the '72, one of the first things on my list to do is replace the thermostat with a new one.(cheap insurance) If the thermostat were being heated and cooled, daily, it should last a long time, but sitting for the winter, they sometimes tend to stay closed or not open completely, which can cause those high temps when the flow is restricted. As far as the temp. of the stat. goes, the 160 will open up at 160 and stay open while you drive, which will promote complete water flow and help keep those temps down. On the other hand, a 180 or 195 will open at their specified temp. and then when the water temp cools back down to less than 180 or 195, your stat will close and then reopen when it reaches it's spec. again. It will open and close many times while you drive. If you're running a newer computer controlled engine, you need the higher temps for things to run properly. If an older pre-computer engine, go with the 160 to keep that system open and the coolant flowing. I've run a 160 since the beginning, and have never had the dreaded overheating problems. I flush the system every 2 years and run a 50/50 mixture of coolant/water and still have the original aluminum Harrison radiator. I've only replaced the hoses and the pressure cap.

 

That's what I always believed, about the water pump. My temp guage reads 30-35 deg higher than my IR thermometer on the t-stat housing.

I replaced the stock rad with an aluminum 2-channel last year. The new fan clutch goes on this weekend, and I will fix the rubber lip on the fan shroud. Oh and I will check the timing too

Anybody install one of the high-flo water pumps? does that help??

 

A 160 degree thermostat will do absolutely nothing for an overheating problem.
Timing that is insufficiently advanced is a common unappreciated cause

The aluminum radiator should have made a big difference. Are the head gaskets blown?

Read John Hickley's article on cooling in C3s.

 

If the flow from a hi-flow pump is going to be restricted by the rest of the cooling system, it will just generate more heat from all the work it is 'trying' to do and make problems worse. Lots of folks think that the more the flow, the better the cooling. That's true...unless you really don't get more flow with a hi-flow pump.

So, buy the pump...if the rest of the system will support it. Don't if it won't.

 

People love to recommend buying a new aluminum radiator, electric fans, and high flow pumps... But before you do, if you don't want to spend a bunch of money, the stock system will work fine when it is healthy. If you don't find the real problem and start buying big expensive components, you may just cover up the real problem. I am using a stock 77 radiator/system with a BBC and I have zero cooling issues.

I would trust the IR gun but members have said that you get different readings with different surface materials, so you might want to check several locations. And before you buy ANYTHING, pull the temp sender unit and stick it in boiling water to check the accuracy.

 

OK, my last post on this.....
For those who have no clue, the 68, 4 speed, manual trans radiator is about 1/3rd smaller than every other radiator in ANY vett, especially those giving you thier nuggets of wisdom in this thread with other year vettes...
Wonder why it was a 1 year only item...It didn't work!
And the fan shroud...look it up if you dont know what it looks like. One year only because.....duh....it didn't work either.
This info is only for those with a 68 small block, 4 speed.
My work here is done.

 

That shroud is unbelievably bad. There also isn't a cooling fin under the car to direct air up to the radiator. I finally gave up this year when I figured out a new 68 shroud would be about half the price of an aluminum/ electric fan set up. Started on it this week.

 

Rally68
I had the same problem with my 68 SB 4sp, I changed the rad' to big aluminum rad' + flex fan and put big shroud + extensions, that solved the problem.
Avner