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Well, after our 39 coupe's debut run last month on one of the hottest days of the year, and going well, although the temp gauge did get quite high, we thought we'd take the car out of town to a car and air show. Great, until we got on to the open road (highway) and the temp gauge starts to climb! Was nowhere near as hot as the other day. The old girl kept boiling! Water pouring out of the overflow pipe. Had to drive about 35-40mph and make numerous stops for water. I thought the thermostat may have been bad and took that out at the show, but no difference. The engine has 300 miles on a motor that's been re-bored, fitted with new pistons, rings, valves valve springs, and valve guides. It has a new radiator core as well. Seems to be ok around town, but doesn't like the open road. Which is odd in my opinion, since the air would be flowing through the radiator faster.

Anyone have any ideas? Water pump maybe?

Cheers

Grant

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Car looked good when I visited Saturday.

Bad luck on the Darfield run. And it was not that hot a day.

Does the (new?) lower radiator hose have an internal spring to stop it being sucked in by the pump?

Is the pump new / rebuilt ?

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Was the block cleaned out when you had it reconditioned? If not all the old rust and junk may have washed out and blocked the new radiator core. Have a look at the top of the core through the radiator cap hole and see how clean it is. Always a good idea to install a filter on the top hose of a rebuilt engine.

David

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I had a '38 Special that would do the same thing. Fine around town, but would heat up within a few miles at freeway speed. The problem was a partially plugged radiator. I'm guessing the high rev's on the freeway just overcame the compromised ability of the radiator to dissipate the heat.

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I am a short time owner of a '39 but have talked with lots of people about them.

One possibility is the sheet metal is missing between the lower radiator and grill. It is apparantly there to fore the incoming air thru the radiator. Not knowing how original you car might be..... it is possible that this sheet metal is missing.

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One possibility is the sheet metal is missing between the lower radiator and grill. It is apparently there to force the incoming air thru the radiator. Not knowing how original you car might be..... it is possible that this sheet metal is missing.
Reasonably sure the all the sheet metal is in place (I visited on Saturday)
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Heater Hose ?

You have got the heater bypassed with the supply & return both connected to engine - pump by about 1m of hose. Cannot remeber a valve or plug in the hose.

A heater is parrallal to the radiator, so what you have is a water hose bypassing the radiator. Not sure which side of the t'stat these are.

This hose will offer little restiction compared to the heater and / or radiator. At high engine revs (55 mph) flow through the bypass hose will be high. As the water heats up NPSH (net postive suction head - vapor pressure) comes in play at the pump inlet. A soon as you vapor on a pump inlet liquid flow drops. NPSH - vapor lock can often be heard (at least on industrial plants that I work on).

What pressure is the radiator cap ? Increasing the pressure increases the boiling point of water (and help reduce NPSH)

I would block that heater hose and go for fast drive along the Main North Road.

Edited by 1939_buick
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I was a bit vague before.

What I was thinking of earlier is referred to as :

"spring loaded valve located in the water passage between the cylinder head water outlet and water pump inlet"

It stops the water from just recirculating around the block and directs it through the radiator.

Danny

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Actually, I should have pointed out that the engine is out of a 1947 Buick Series 50. The water pump pulley is larger meaning less rpm. Would that make somewhat of an impact? And would that mean that the spring plate in the thermostat housing would still need to be there? You're right Allan, there is a loop of about 1m of heater hose from the inlet to the outlet. I'll try and get some bungs from the Vintage Car Club tomorrow. I have this week off to work on my Corvette, but it sounds like I'm going to be conned into doing Buick stuff!

Cheers

Grant

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The water pump pulley is larger meaning less rpm. Would that make somewhat of an impact?

Flow rate is proportional to speed. Pressure is proportional to the square of speed. But engine speed varies a lot anyway.

And would that mean that the spring plate in the thermostat housing would still need to be there?
My guess is Yes. Some water will need to be bypased
You're right Allan, there is a loop of about 1m of heater hose from the inlet to the outlet. I'll try and get some bungs from the Vintage Car Club tomorrow.
Interested to see if its makes a difference. I think it will. Anything could block the hose:- even a bit of steel / bolt with a hose clamp
I have this week off to work on my Corvette, but it sounds like I'm going to be conned into doing Buick stuff!
As it should be ;)

And anything will be better than working on that rice burner beside the Buick.

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Without the spring and plate fitted the water will go from the head outlet back into the water pump inlet and just recirculate the hot water around the block. Sure "some" will go through the radiator but I'd say not the majority. It has to be there for the system to work properly.

If you're not sure it's there, it's definitely worth the time to check it out.

I've seen a few thermostat housings turn up on ebay and they all seem to have the spring and plate missing. Not sure what the logic is/was for removing them.

Danny

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Do not bypass the heater - - - Close the heater valve or block-off the inlet and return heater lines. The heater is not as good a heat exchanger as the radiator.
The heater is not in the circuit. Just bypassed without valves or anything to block the flow.
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To clear up one thing, the "coolant bypass valve" as it's being discussed, does *NOT* bypass the thermostat in anyway. Note the construction of the thermostat housing and pump, etc. I had my whole system apart a couple years ago chasing my overheating problem.

This bypass valve allows the coolant to circulate through the heater core. This plumbing is below the 'stat, however, so no matter what happens, nothing will flow to the radiator until the thermostat opens.

What are the details on this engine, etc? Did it "just start doing this?" Ever have any success on the highway? In my case it was a clogged radiator that also leaked a little, as the shop told me. Boiling it out ended up being what took care of my problem, nothing but the radiator. A "different radiator cap" was mentioned...these are non-pressurized systems. ;)

Don't run it without a thermostat, been there done that, it instantly seemed to make it great but under the right conditions it got even WORSE. The water will flow too fast through the radiator and won't dissipate its heat. All I know about 1939s in particular is that the front grille doesn't allow too much air through it. However, if you had good running before the rebuild of this engine that would rule that out...it would have had to been flowing enough air back then. Ive heard of that talked about as words of warning before, so if it were my car my first action would be just yanking both grille sides out and trying it like that.

If you can spin your water pump easily, it's not totally binding up, I cant see it being the problem...the impeller fins would have to literally be eroded away, which could happen if a neglected system just rotted away for years. My '38 sat for a quarter century and upon disassembly the impeller looked as good good as new, structurally. Not shiny and nice but all there.

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My suggestions -

• Do not bypass the heater - This can cause overheating.

• Keep the heater valve closed.

• Do not operate the heater in an effort to reduce overheating.

• Make sure the thermostat bypass valve is installed and functional.

• Make sure the lower radiator hose has a spring to prevent collapse.

• Make sure the radiator core isn't plugged.

• Installing a 1950-52 Roadmaster fan would help at low speed.

• Remove the block drain plug - If no (or little) coolant comes out, clean-out the water jacket.

• Install a Gano inline coolant filter after block clean-out to keep radiator clean.

Grandpa

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To clear up one thing, the "coolant bypass valve" as it's being discussed, does *NOT* bypass the thermostat in anyway.

Not sure I'd agree with that. It's sole purpose is to "bypass" the thermostat (and the radiator as well) when the thermostat is closed.

Don't run it without a thermostat

I'd agree with that for sure. The engine needs to be kept at the right running temperature for optimum performance.

If I was a betting man Grant, I'd put my money on crap in the radiator.

Many years ago when I had my radiator tubes cleared out with a rod shoved through them, the fool radiator repair bloke somehow, or for some reason, blocked the overflow tube. First time the engine got up to temperature it blew out the water pump seal. If you let someone bugger with the radiator, check its clear. Something else you may or may not have looked at while you had the water pump out is the backplate behind the impeller. 2 of my pumps where badly rusted and had a lot of rust pits that where almost through the plate. I made a liner from copper shim to prevent leaks in the future.

Danny

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Thanks guys.

Some details re-the engine. The car was bought as a non-runner from Lakewood, Colorado 2 years ago. Unbeknownst to us, it had an early 1947 Series 50 engine in it. The radiator was re-cored with a new more efficient core. When the engine was apart, I cleaned out the water passages when I installed new frost plugs. The bottom hose does not have the spring in it. I'll see if there's one at the car club today. It doesn't have the coolant bypass valve. I flushed it out yesterday, and got clean water. Today, we're getting some bungs to block off the heater pipe inlet and outlets. And the thermostat is going back in. I have been caught with a faulty thermostat in my 39 Chevy, and ran it quite successfuly without one. As Allan says, the car has all it's sheet metal required for directing air flow. The water pump was in good order when we had it apart during the rebuild. So, the things to try are, installing the bottom hose spring, installing the bypass valve, and putting bungs in the heater pipe inlet and outlets. Then we'll see how it goes.

Thanks again.

Grant

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Not sure I'd agree with that. It's sole purpose is to "bypass" the thermostat (and the radiator as well) when the thermostat is closed.

True...should have clarified my definition of it...what I meant was that it doesn't bypass the thermostat and let coolant flow to the radiator anyway. Thanks for preventing me from confusing anyone :D

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No Danny, we don't have one. Put bungs in the heater inlet and outlet thisarvo, and still boiled. I had a look at our vintage car club parts shed and couldn't see anything. Any idea where to get one? I guess I could put a WTB on the parts forum. BTW, the bottom hose is not compressing. Strange that it only goes really bad when it's on the highway!

Cheers

Grant

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No Danny, we don't have one. Put bungs in the heater inlet and outlet this arvo, and still boiled. I had a look at our vintage car club parts shed and couldn't see anything. Any idea where to get one?
I did think the heater bungs would fix it.

Worth phoning Owen C who visited your father some weeks ago. I do not think I have any in my collection of parts. No idea if any of my 2 cars 15 miles from you have fitted. Will send you an email when I get home (at work now)

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Grant

You had access to a lathe for the fender lamp lenses. Make a washer about 2mm smaller than the bore in the housing and use a spring similar to the one in the photo on ebay.

1936-41 Buick Thermostat Housing GM# 1295238 : eBay Motors (item 200396105269 end time Apr-16-10 21:01:56 PDT)

It will soon let you know if you have fixed the problem until the correct spring can be acquired.

Danny

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Hey, I'm no tuning expert, but in reference to overheating, seems like I always see suggestions like "carb set too lean" and "timing too advanced", or the opposite, or something like that. Sorry. The details just won't ever stick in my feeble brain.

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..Make a washer about 2mm smaller than the bore in the housing and use a spring similar to the one in the photo on ebay.

1936-41 Buick Thermostat Housing GM# 1295238 : eBay Motors (item 200396105269 end time Apr-16-10 21:01:56 PDT)

The engine in Grant's car is 1947, so not sure if the 1936-41 ebay part would fit. Grant's father also has a 1938 so can check if they look the same.
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Grant:

I had a 39-90 for years. It was a chronic overheater until I got a lot more miles on it. The friction in a rebuild can overwhelm the cooling system. Your engine is freshly rebuilt with new bores. I would get at least 2000 miles on that engine before you do much more to the cooling system. Drive it at night regularly to rack up some miles, bring extra water if necessary. I found this did a lot for my Buick.

You could have a head gasket leak or crack in the head that's sending exhaust gases into the coolant. Most shops have a sniffer to detect exhaust gases in the coolant, might be a good idea just to make sure that's not the problem.

I think the thermostat bypass valve is not your problem. I believe that little shuttle valve to turn off the bypass was not used in a 47 engine -- instead there is just a built in calibrated orfice that passively controls the amount of water recirculated instead of going through the radiator. It has no moving parts.

I did put an RV flexible fan on mine and it was most helpful. This fan was a bolt on replacement for the original and it was a tight fit -- but it cleared everything and really increased the air flow. I suggest you keep an eye out for one, most auto parts stores sell them in various sizes and shapes.

Make sure the timing is set properly and that the centrifugal advance is working on the distributor. Retarded timing really ads to the cooling system load. Make sure the fan belts are tight.

Mostly, though, get some miles on your buggy.

Good luck down under!

Bill S

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Here's an interesting thought. The water pump and pulley is a 1947 one and a larger diameter. A visiting engineer from the UK suggested that because the fan is going slower, it could be working in conjunction with the 39's front end design to create a wall effect at highway speeds, and preventing air from flowing through the radiator. Thoughts?

Cheers

Grant

PS sorry to keep going on about it!:)

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Wow !!!! That's out there.

I guess anything is possible but I think I'd leave that at just a thought:rolleyes: .

It seems you have a ready supply of parts there for a cheap trial and error test. Try the pulley from your father's car.

You said you had no bypass valve but the question now arises that maybe you have the later type housing.

Is it the later type housing with the fixed 1/2" hole??

If so, bypass is not the problem. If not, try the bypass from your fathers pump or use it as a sample to replicate. (I hope you get on well with your Dad:p)

I did put a six blade fan from a Commodore on mine. It is also a slightly larger diameter. It looks the part and unless you are a Buick nut no-one would ever know it's not original. The difference in the air sucked through the radiator was great. I'm one of those that doesn't get bent out of shape over not being 100% original.

Danny

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My '39 has yet to overheat but using one of those new thermometers that you point at something and it reads the temp..... it get to 208+ too close for comfort on a 105 degree day in Texas traffic. (I have no problems on the open road, only in town)

I am thinking of several things in no particular order.

(1) rig a couple of the patio misters to a lawn sprayer and have a way of turning it on from inside the car. It would put a mist of water on the front of the radiator. Again, only needed in town.

(2) an electric pusher fan that would be mounted in front of the radiator (high where there seems to be less air flow) it should be easy to find these on modern cars. although they are 12 volt, they would run half speed on a 6v system.

(3) slightly pressurise the system. Each pound of pressure, raises the boiling point about 2.5 degrees, 4 pound pressure cap would give a 10 degrees cushion. I have found a nifty tank from a Chevy Citation (about 1990) that has three openings. One is about 3/4 inch and would allow tapping into the heater hose. The second one is the pressure relief at the radiator cap and the third one...... not sure what it would be used for. The tank is plastic and is roughly 6 X 8 x 8 deep. I have not started to search for radiator caps that are calibrated for low pressures.

People that have offered their opinions, think that the '39 system would tolerate 4 psi but all seem to think a 12-14 psi cap might cause the water pump to leak. This is all opinions as none of them have tried it.

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Here's an interesting thought. The water pump and pulley is a 1947 one and a larger diameter. A visiting engineer from the UK suggested that because the fan is going slower, it could be working in conjunction with the 39's front end design to create a wall effect at highway speeds, and preventing air from flowing through the radiator. Thoughts?

Man, that takes me back 20 odd years back to first year engineering. It is correct that because the air needs to flow around an object in the way (like a bar on a grill), at high speeds, it creates an area of high pressure in front of the impediment - if the geometry is such that the bars are close enough together at sufficient speed, the air will act as if it is hitting a solid object. Aerodynamics can be really interesting.

That may be why the grill design on '39s had a running change to fewer bars...it may have been creating this issue.

As an experiment, I'm with the others who suggest taking the grill parts off to see if it makes a difference. At least then that might help to verify whether or not you are having an air flow issue.

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Thanks again to everyone who has offered great advice.

Had another play today, and compared to the 38 Sedan, the pulley is way bigger. Also, the 38 has quite a small diameter fan compared to the one the coupe has in it right now. Something else to consider is the size of the gaps in the radiator cores. The 38 has the same pattern as the 39 coupe, but it's a coarser one, for want of a better term. In other words, the air has less of a fight to get through. Tested the waterpump today and it appears to circulate the water well enough. I'm really keen to try a smaller pulley and fan to see how that works. I should point out as well that it seems the 38 Special's engine is in fact a 37, going by the engine number. I don't know whether it's a left over 37 engine they put in from new, or a replacement. But NZ assemblers were known to not waste anything!:)

Cheers

Grant

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  • 3 weeks later...
So Grant...

What news have yee ???

Danny

Sorry! I've been flat out with my Corvette!

The good news is that after having a dig around the block drain tap, and putting a few miles on her, she's calmed the hell down! And getting better all the time. Took her for a run today and never missed a beat, although we do need to get that noisey 1st gear replaced, and the steering adjusted. I'll do the steering this weekend I think. On Tuesday, she gets her rear carpet and trunk done. That means all we have to do is track down a running board trim piece and we're done! We're entering it in the Restoration of the Year with the local vintage car club post vintage section. Here's hoping!

Cheers

Grant:)

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Whats the deal with the "noisy first gear?" Is it chewed up? Or just making a howling/whining noise? If its the latter, it's supposed to do that. 2nd gear is a little quieter. Its all because of the torque tube. The howl resonates in there. ;) I love it.

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