A friend of mine has a 61, base motor that was rebuilt two years ago and has been overheatin ever since. The engine had been bored out to a 301 years ago, but not bored again. It never ran hot before the rebuild. Here's what we've done. Adjusted carb so it's not running lean. Changed out distributor because vacuum advance was not moving dist. plate. Timing and dwell are good. Installed new Dewitts radiator. Factory shroud. Replaced fan clutch and ran without it for awhile. Changed thermostat 3 times. Only thing left is the water pump, which was new at rebuild. A couple of friends have suggested the head gaskets are flipped or the holes are too small over the water jackets. Today we checked the temp at over a 30 min. idle. Neck after 20 mins was 170, upper hose at 120, lower hose at 110 and water pump at 145. Expansion tank was 120. After about 40 mins. the guage and neck were at 200. On a cool day below 70 while driving, it will not overheat. Anything above 70, it will get up over 200 and be boiling. I'm not sure if were getting a good flow now. Pump or head gaskets? Blockage? Opinions?

 

Thats the normal operating temperature, for the system at that time at that test condion. Since when is sitting an idling for 30 minute a normal operating condition? (except for parades?)? How does it operate crising along 40-50-60-70?

The whole set up is a thermodynamic system, sitting and idling and only getting to 200 doesnt seem bad and is only achieving its thermodynamic balance. Ram air is very good. You have discovered the thermodynamic inefficiences of your system (our old cars) sitting and idling.

My late model truck just runs at the thermostat temp 190, but it has a giant radiator, late model design, I dont think our 50 year old cars were designed that way.

Now if its boiling at 200 water boils at 212, then the radiator cap isnt keeping enough pressure, basic physics.
But if its blowing up the hoses, blowing out over pressure over your cap setting, then you have a compression or head gasket leak (unlikely after a good rebuild).

The fan/shroud/radiator air gap leaves alot to be desired, remember path of least resistance. Seal up the gaps ( I have used roll bar padding, its a high temp material). Does a sheet of paper suck up to the radiator?
Seal all that up it may idle for a long time at the thermostat temp.

Now what is the normal driving temp? All your equimpment seems very good, that radiator is excellent, Maybe could you be over worrying it under really demanding conditions?

 

Thanks, but I realize that 200 is not overheating. Normally it was taking only about 15-20 mins. to overheat and get up to 200-240. He doesn't like letting it get up too high all the time because it will just keep climbing. It is an improvement since the radiator swap, but still overheated the other day on a test drive. It gets up to 220-240 on any day on short drives so he doens't get very far from home. Even getting on the highway does not bring it down unless the air temp is below 70, then it will stay below 200. The idle was a test to see how fast it would get up, compared to what it has been doing. He's thought about trying a high volume water pump, but they're pretty expensive too. I have a 57 fuelie that will idle all day and not get anywhere near 200. He's very frustrated.

 

sounds to me like the water pump providing everything else you state checks out.....it's the highway cruise speed that tips me off. spring in the lower hose??..good luck

 

One fact that you mentioned but no data is the idle timing with the VAC connected? You need about 26*@ idle to minimize EGT. What is the temperature of the exhaust manifold ports after 20 minutes idling? Normal about 450*F -500*F.

 

+1

 

There is a spring in the lower hose. I didn't check the exhaust manifold temps yesterday. I didn't mention that the heat riser valve is open also. He's wants to remove the thermostat today and see what that does. He's had trouble with them before, so we'll see. The new distributor does not use vacuum advance. We installed an aftermarket dual point with mechanical advance. I'll check the timing again this week. I guess the next thing is to replace or check is the water pump before we pull the heads to replace the gaskets. I just don't believe it's the head gaskets causing the problem, but a mechanic friend of his is saying it is.

 

What exactly does this mean? Sometimes too aggressive of a rebore can make a motor run hot. Less metal to dissipate combustion heat.

 

You've said that timing is good, but not provided specifics. What is the timing at idle? Off idle?

I've noted that you installed a distributor with mechanical advance only. I'd be much more tempted to install a distributor that also includes vacuum advance before I'd even think about changing head gaskets. Nothing about the problem you've described says "head gaskets" to me.

Jim

 

It was bored .030 over years ago. It was not bored out any more on this rebuild. It never ran hot until after this rebuild. We've set the timing at different degrees to see what it would do. Overheated at all degrees. It had a vacuum advance to begin with and overheated, so we switched it out. I think it's at 8 degrees right now since it has the mechanical advance.

 

I agree. Stick w. the OEM distributor w. the correct VAC for your application. Connect VAC to a full time vacuum source. Base engine w. stock cam should pull 18-20 inches Hg @ idle. You need the additional 16* that a VAC provides @ idle to minimize excessive EGT.

 

We did that already. We had it connected to the carb base to get full vacuum. Still overheated. It has an edelbrock carb on a stock intake.

 

A .030 bore on a SBC shouldn't be a problem....and if you changed out 3 T-stats I don't see how running without one will prove anything (they control the MINIMUM temp when they are working and I doubt you had 3 bad ones). However, I assume you didn't install them upside down. I'm thinking the vacuum advance would make things run cooler but not solve the excessive over-heating problem stated. I'm back to the water pump or else blockage somewhere due to the engine overhaul. Its just too coincidental that the problems started after the rebuild.

 

What is the vacuum reading at that port and what VAC are you using?

 

It's been awhile, but the vacuum was around 16-18. But like I said, it still overheated. We've been fighting this on and off for the last two years, so there's not a lot we haven't tried. That's why he started replacing things. The original radiator had a leak in it, so he had it repaired and it came back worse. It was ruined. He replaced it with an aftermarket radiator and of course still ran hot. That was last year. He just bought this DeWitt's a couple of weeks ago and still the same problem although it did help. He pulling the thermostat for grins just to see what happens. The next thing will be the water pump.

 

Try a..........I hate to say it, direct drive flex fan, , I think your air is bypassing the rad. I have had the same experience, I live in arizona.

temp just keeps climbing......... Until I really got serious about sealing up the gaps and really pulling some air through the radiator.

Test If a sheet of paper will stick to the front of the Rad, it should.


fan clutches can be failed even when they still turn, the are just slipping so much that they seem OK, but really are not pulling enough air.

 

With a 50/50 mix and a 15 psi cap you'd have to get to about 275 to boil. What many think is boiling is simply "expanding" because they over filled the tank.

My first recomendation on any cooling issue is to varify the gauge reading. I didn't see anywhere here you mention an IR gun. Check the gauge at ALL ranges from 180-240. if you have a bad sending unit it will go non-linear above 190 and could read 20-30 degrees too high.

The second thing I question is the coolant/water mixture. Some people think that 100 coolant is a good thing, it's not.

Third, I ask "when" does it overheat? Idling or driving or both. Idling only is usually the vacuum advance and/or timing issue. Other times it's a fan clutch problem.

Keep in mind, 200-210 isn't going to hurt anything and if we didn't have gauges you'd never know anything was happening. New motors run a little hot until they break in, say 3000-5000 miles.

I'd go back to the stock distributor and vacuum system as it seems the farther we get away from the factory settings, the harder it is to get these to work right.

 

We've tried all of that except the paper test and sealing around the top of the radiator, but we will seal it off. We did use an IR gun on everything putting off heat and the water neck read exactly what the gauge was reading. Everything else was cooler. It's probably has more anti freeze than water but not 100%. The engine does not have that many miles on it because he can't drive it very far. It is broken it though. Check my first post for readings.

 

What were the readings when it was boiling?

 

Um, wait a minute. Either it was bored .030 or it was bored to be a 301 (which means a .125 bore); it can't be both. Which is it?

Also, your first posting noted that the vacuum advance wasn't working. That led you to conclude that you should just chuck it and go with a mechanical-only advance mechanism. It seems you haven't really given a vacuum advance a fair trial. You should. You really, really should. But if you are determined to run without vacuum advance, your initial timing ought to be in the 12-14 degree range.

In your most recent posting you said:
This isn't helping you. Run as much water and as little antifreeze as you can while still providing adequate freeze protection. Water is a much better coolant than antifreeze.

Jim