weirrd cooling system issue with small block chevy

One heater hose to the pump one to the intake are the radiator. Has to circulate.

 

snap a few pics

ALSO... do you have access to or do you know anyone with a RayTech? I don't trust sensors and gauges 100% either.

 

It sounds like a slow T stat to me. If I understand what you are saying it always goes back to normal operating temps. It just sometimes takes longer and the gauge shows a higher temp until the stat finally opens. You said it boiled over a little bit. If you mean it puked some coolant, that still might not be a serious problem. Some of that is normal we just don't notice it until we get worried and watch the gauge like a hawk. This goes on all the time on a daily driver but the coolant recovery tank keeps us from noticing.

I don't worry about momentary 220 pulses. If it doesn't come back down then you have a geyser. You didn't say you had a geyser yet. If it were mine I'd put a 180 stat in it and a coolant recovery tank. You can get some street rod units and paint them flat black so they don't stand out.

 

thanks guys. I'm going to try another 180deg tstat this weekend..

coolant recovery tank is on my todo list too.

 

This is always a personal preference thing, but for a hot rod that gets used mostly in the warm weather, I'd go for a 160 Deg. stat. The 160 stats keep my hot rods in the 180 range in the hot weather. If you drive it in freezing weather then the 180 stat will make the heater air nicer on the tootsies. JMO

 

by heater, do you mean transmission

 

So i finally got a chance to use my buddies coolant system tester.


So, i did two tests on my motor. The first test i presssurized to 15 psi. After about 30 min it had leaked down to about 10. Then i started the car with the system closed. Ran it up to about 3k and no pressure. Removed my fan belt, just to see what that would do and again no pressure. I thought about doing another test with the thermostat out but that would be a chore.

What do you guys think?

The results seem to indicate no problem? Im thinking about opening the vent hole in my thermostat to .25 and seeing what that does. Id still like to know the cause but i bet that fixes it.

 

It would take longer to warm up in cold weather with a 1/4" hole.

I drilled two 1/8" vent holes in my roadsters thermostat and it took about four miles to get the coolant fully warm.

Installed another same brand 180 stat - a Stant I think - drilled with only one 1/8" vent hole and the engine coolant is warm in about a mile and a half of easy 35 mph driving.
(Same route in both cases.)

Takes a little longer for the engine oil to come up to temp with either thermostat.

 

I think I've had an *** load of Chevies and never needed to drill a hole in the thermostat on any of them. In hotrods or daily drivers. Personally I think it's an internet wives tale that keeps getting p***ed around like replacing it with a washer. Wouldn't GM put one there if it was needed? I'm sure it doesn't hurt anything but I don't believe it cures anything either. JMHO

 

<P><FONT color=#ff0000 size=4>"The pressure comes from the water expanding as it gets up to temp. The pressure doesn't come from the water pump.</FONT><FONT size=2> </FONT><FONT color=red><FONT size=4>Did you get it up to operating temperature?"</FONT></FONT></P>

I was under the impression that a crack in the exhaust port would cause&nbsp;the system to pressurize.&nbsp; More-so&nbsp;while cold because the gap would close as the metal expands.&nbsp;&nbsp;

I did think about running it through a cycle.&nbsp;&nbsp;&nbsp;Although i'm not sure what i could prove?&nbsp;&nbsp;&nbsp;Shouldn't i expect it to pressurize somewhat during warm-up like you said?&nbsp; If so what is an acceptable range?
Sorry but i've never ran these pressure tests before.&nbsp;&nbsp; Chevy's have always just worked for me

 

My money's on a bad thermostat. New don't mean it's good

 

If you pump it up to 15lbs and have a leak of any kind the pressure will immediately start dropping. You can watch the needle drop. It won't hold pressure for 30 mins. It will be at zero in no time. Your system is tight from what you have said.

Actually if you reved the motor and the pressure went up on the test gauge then that is a sign of a possible blown head gasket. The combustion gases would be pressurizing the cooling system. We have used these gauges to test for a blown head gasket.

 

Replace the thermostat with a robertshaw high flow. The kind that don't look like a traditional thermostat. Special order it if you have to.

 

Have had some what of the same problem here in AZ. When it starts, I just replace the WP and T stat with a Stewart pump and Shaw T stat (160, if a emiss veh, a 180) and have never have the problems again, even in the oc***ional 120 + temps and AC on. When I put together a veh with a SBC or BBC, it always gets the Stewart/Shaw treatment from the start. Best source for the the stuff I have found is Speedway Motors, last pump and stat I bought was about $70 and $15 each plus about $12 S&H. About 3 days to Mesa. I just wish they made them for early Cad/Olds!! LOL The Stewarts are claimed to be NASCAR quality, bigger shafts, bearings, closer tolerances, etc. I do know they have always solved my heat probs. Good Luck. Dave

 

PS-try with NO stat as an experiment, and see what happens

 

Not necessarily an old wives tale . . . I never had any trouble with air locks in my roadsters Buick engine, then I had a couple of them.

Drilling a hole in the thermostat cured that prob, and like you say it doesn't hurt.

 

Ever compare the Chevy thermostat with the Cad/Olds?

Most stats seem to be about the same size.

I installed a Chevy stat in a Cleveland 400-M.
It fit, but it didn't have the byp*** hole plug like the Ford did.
Kinda shot myself in the foot there.

 

Hmmm... since this thread is back from the dead, I guess I can hijack it again.

Turns out the heater I installed in my truck is hooked up correctly. One hose to the water pump, one hose to the intake.

With no thermostat, it runs about 150 usually, but hot days and traffic bring it up to 180.

If I put a thermostat in it, it just goes straight to 230 with no end in sight. I used a 180 stat, no hole drilled. I thought about trying drilling a hole, and byp***ing the heater, see if it goes away.

Any thoughts?

I'll see you guys again with this thread resurfaces in a few months!!

 

Are you filling the rad to the top,if no recovery tank is used and you are running coolant,fluid level needs to be at least 3" from to of rad for room for expansion. Don't know what dist you are running but 8 btdc is a little low.Are you running vacuum advance to manifold.

 

***uming we're talkin initial and not total, 8 BEFORE TDC should be fine. Most stock SBC's run 4.

 

Ah Hell. I don't know why this was on the 1st page, but I just realized it's TWO MONTHS old. So, I guess it's all moot. I never said I'd make a good detective

 

Get a Shaw/Stewart or a high volumn thermastat from NAPA or Advanced. Had the same problem a few years ago. The new thermastats are made for FI and don't work well with carbs.

 

Take a look at the "Fail Safe" Brand of thermostats. Although I use a pump riser with a 6Cyl water pump, this has really helped tremendously. Pick one up for under $12 at your local autozoners

 

I have the coolant about 2 1/2 inches from the top of the cap, just covering the cooling p***ages by about 1/4".

8btdc is initial, i'm running mechanical advance... I've played around with 4 and 6 and this is really where this motor runs best..

 

I agree. The cheap *** made in who knows where thermos are just that. The above mentioned source sells thermos for 16 bucks or so. Seems to me that ain't much to solve a big problem.

 

No vacuum advance?

That could be your problem right there.


Fwiw, GM engineers started the vacuum advance selected to ported vacuum bit to force the engine to run hot on the low end to improve the smog situation.

Many of these engines - if not most of them - also had a thermostatically controlled vacuum switch.
Although, most times, the engine had to be on the edge of severe overheating before the thermo vacuum swich would open and apply full time manifold vacuum to the vac advance can thereby bringing the engine down to a reasonable temperature.

There are vacuum advance cans available that allow you to run a fairly big cam with its usual low manifold vacuum levels.

I'm betting that part - if not all - of your overheating is due to lack of vacuum advance.

People have a hard time believing that timing can create an overheating problem, but, if you have a mechanical - racing type - distributor and retard the timing quite a bit will it not overheat?
It will.

You ought to be able to scrounge up a stock vacuum advance distributor.
Make sure you have the vacuum advance connected to full time manifold vacuum.

Give it a try and quit looking for band-aids....

 

I said that because I first started reading about drilling holes in Flathead thermostats. I thought it was odd but I kept my mouth shut. I was new to flatheads. It wasn't until later that I opened the box to look at a NORS Flathead Thermostat that I had picked up...



There it is at 9 o'clock. This NORS factory flathead stat has the vent hole. Less than .125 but it's there. I can't recall ever seeing one in a Chevy stat.

As far as the level of coolant in the radiator, I let it find it's own correct level. I always bring the engine up to operating temperature with the cap off and the radiator full. At that temperature all the expanding of the coolant has taken place. When it cools back down the level may fall pulling a vacuum but when it heats back up it will rise to the full level.

Without pressure gauges in the system we really don't know what pressure is on the cooling system. Just because you put a 15lb cap on it doesn't mean that it will automatically run at 15lbs. It means that it wont puke until it reaches 15lbs. It could be operating at anything below 15lbs and you would never know. You can have a 15lb cap but the system only generates 6lbs pressure. A 7lb cap would work fine too. I ran 2 SBCs with stock Ford flathead radiators with no pressure caps at all. A stock mechanical fan and the stock radiator were up to the task and nothing more was needed.

 

Not sure how much help this is but my 61 Chevy truck with 400sbc would boil over like a b-tard, burped it trying to get that air out of the heads, and then changed to a 20psi and that fixed the problem. double checked the temp with a manual gauge plus the electrical and it stayed at 180 with a 180 t-stat. it would spike 200 and then open

 

I think if you haven't gone to a "closed" system yet.....I'd do that. A good recovery tank with the pickup tube/hose near the bottom of the tank, a good closed system type cap and completely fill the system with coolant....allow no air pockets, purge it really good. Now you have better controlled expansion in the system without the rapid expansion of a big chunk of hot air.

 

OK, I'm not keen on this closed system set-up. I have a 68 327 with just the alternator. I have the Moon recovery tank Parallel to the radiator. Recovery tank bottom hose goes to the top of radiator neck. The top hose of the recovery tank to the bottom(ground). how should you fill the radiator and this would be consider a closed system? Thanks.

Ken