weirrd cooling system issue with small block chevy

A few months ago, after 8 months off the road i had some overheating problems as my T coupe was starting up. Essentially the car would almost boil over for the first two openings of the thermostat and then would be fine. If figured she just needed a thermostat so i did that it it seemed to alevaite the problem but now it happening again. Yesterday i took her out, she hit 200 and then opened, went to 150. THe car then went up to about 210-220, boiled over a little bit and then hit 170. They she ran between 170 and 185 the whole rest of the ride.

I'm running a good stant thermostat and even drilled a .060 hole for extra venting. My rad is SLIGHTLY higher than my water neck so i don't think it's a bleeding problem. I run a mustang 3 row radiator, trans cooler, fixed mechanical fan (off a 57 chevy) and a very well designed fan shroud.

Could it be my pump? Cap? I guess i could try the cap pretty easily but i'm not sure it makes sense. Any ideas?

 

You may have gotten a new cap that is defective, or, you don't mention the pound rating of your cap and that could be the culprit .Unless you are running lean, with a lot of compression, a 7 lb. cap should suffice. Hope this helps. gh

 

Sorry the first mention of cap should be thermostat .too many paint fumes in here!

 

possible air bubble?

 

oops.. i meant thermostat. I put a new stant thermostat in it , 180deg.

The cap is a 13lb stant.

 

Try that 7lb radiator cap and let it find it's level and just keep an eye on the temp guage. I got that info here last year and mine runs a steady 185-90 all day long now.

 

that's an interesting thought. Without a coolant resivoir, are you suggesting the coolant level might not be right with the car running? Essentially the thermostat could be left "Dry" untill the coolant really starts moving. I could try a 7lb cap if i'm going to play with it anyway.

 

I had some probs with my T when I first got it on the road spittin water when shut of and it wasn't hot. Replaced cap[new] with another new on prob solved. You guys noticed that thermostats that you buy now seem to bang open and shut rather than opening slowly ?? Even in the 90 degree weather we have here in Phoenix now the damm temp guage bownces from 160 to 190 ,and won't hold a steady temp. I've tested the things in a pan of hot water and watched as the temp of the water rises and my 180 doesn' t even start to open untill 185 or so. Tried 3 different one with the same result. Years ago a 180 would start to open in the low 170s and be fully open just over 180.

 

it's just weird. 2 years on the road and it ran hot, mostly because of a ****ty fan shroud. Now i have that solved and i have this issue..

 

A source for good, reliable thermostats...though not necessarily cheap...http://www.stewartcomponents.com/

 

Rodwerkz,
Funny you should mention the Stant Stat.
I put a stant T stat in the Pusher the winter before last, a 195. Trying to get enougnh temp to make my heat work. Since then every time its completely cooled off and I restert it runs to between 220 and 230 the first time it opens, after that its fine. I wonder if that's common to the newer stant stats???

 

Also keep in mind if the thermostat has the little vent hole, it needs to point to the highest point of position,so that air can bleed.

 

Question: Do you have a heater hooked up or do you have the heater outlets plugged? I say this because the heater works as a byp*** when warming up the engine. I had the same problem on my old 51 gmc truck and when i replaced the rotten heater hoses I found that the hose adapter at the thermostat housing was full of rust. Cleaned it out and presto, no more +200 then ok syndrome.

I do however have a 98 Silverado that does a similar thing, goes up to 200, then opens, had the stat replaced (after the dreaded manifold gaskets failed) and still the same thing. Did it from buying it new.

Make sure a byp*** hose is there in some form.

 

no heat.. it's an open wheel hotrod

I get what your saying but i have run with no byp*** before, plugged them a few times as well.. Plus in alot of vehicles the heater byp*** get's closed when the heat is off .. Leaving them open all the time is pretty much the norm now but especially in your pre-80's GM's they used those stupid vacuum acutated valves.

 

The byp*** can just be a hose from the water pump to the manifold fitting. Doesn't need to have heater.

 

so go from the water pump to the intake?

anyone got a pic? I haven't seen that done before..

 

Seems you don't need a bypas in a sbc, didn't think so, it's all connected.

"Theoretically, a water pump byp*** hose serves two functions: it promotes quicker warm-up on cold-start, and helps prevent water pump impellor cavitation. Although most small-block Chevys have internal water pump byp*** p***ages, the big-blocks do not, so in theory an external byp*** hose is required. However, there are two workarounds that should let you slide by without connecting the byp*** hose. First, if coolant always circulates through the heater core whether the heater is on or off (this is the case if there is no shutoff or vacuum-actuated valve mounted in-line on the heater transfer hoses or screwed into the intake manifold), the constant circulation pathway should be sufficient to accomplish the byp*** function as well. Alternatively, you can experiment by drilling several small 1/8-inch holes in the thermostat's mounting flange underneath the water outlet housing.
One other thought: There was a special hose with a molded-in bend (GM PN 1485552) used on big-blocks with short water pumps (68-and earlier p***enger cars and all Corvettes), but it may be too short for use with the long pump."

 

I agree about newer thermostats acting like an off/on valve instead of modulating slowly, like they used to.

But a cause could be a head gasket or cracked head that alows compression air into the cooling system when cold. Then when the temp gets up it stops leaking. I've seen this more than once.

This is not the first thing to check, make sure nothing else is wrong.

Frank

 

I'm having a very similar problem now!! Before I put a heater in my '57 truck, it cooled fine, but since I put a heater in it I can't run a thermostat at all! What would you suspect? I ran both heater lines into the water pump, should one be in the manifold?

 

I guess that is possible. I actually did the head gasket and inspected the head a few months ago (after the problem first occured). I didn't see any visible cracks and the original head gasket did not appear to be compromised buty ou never know. It's not like i magnafluxed it or anythign.

I skipped a second round of head bolt retorquing but don't think that could be the issue. I rarely do that anway unless i'm working with a race motor. this is a ****py sbc..

 

If you have any connections that have a coolant pressure gauge borrow it an test the coolant pressure. Start the car while cold and run it through the heating cycle and this will tell you if your fighting a compression in the cooling system problem>>>>.

 

If you ran both lines from the water pump you are essentially by p***ing part of the coolant from flowing into the radiator. The hoses are pumping water in a circle straight to the heater. Unhook the heater and see if the problem goes away. I would hook the 2nd hose to the intake>>>>.

 

If the sending unit is deep in the block, it will always read a little hotter than where the thermostat opens. The thermostat opens, but takes a minute to get the cooler water to the gauge.

If you aren't running a heater I would recommend running a small hose from the intake to the pump.

Did you top off the rad right before you drove it after the sit? Could have just been too much water, leading it to puke to whatever level it wanted. I would let it puke at temp, then check it after it cools. If it's at a reasonable level, I wouldn't top it off.

 

when i stuck my coupster together i put a 7lbs rad cap on it, it would over heat like a mother, i put a 12 or 13 lbs on her and it took care of it all, so i wouldnt go with a lighter pound one.

jeff

 

1st try a genuine ACDelco thermostat part#131-87 (fits most year sbc's until the newer stuff (and don't drill any holes in it)). The stants and most aftermarkets are total ****. Keep in mind the longer the coolant is in the radiator (reasonably) the better it gets cooled down before making it's return trip to the engine. It sounds as if you are covering your bases in the fan shroud and blade department so that should be alright. Next... the radiator itself in your application... is it a small (top) tank or large tank and is it standing up or turned sideways? The reason I ask is that for every pound of pressure you add to your cap you increase your boiling point 2 degrees... can't see the radiator from here so you tell us... or better yet snap a couple of pics of the radiator layout for us. Hope this helps.

 

take the thermostat out and put in a restrictor washer in its place

 

I'd say it's a mid-sized tank, it's a top to bottom flow radiator.

 

Don't do that unless you only drive it on constant 70º days at constant speeds and al***udes.
Otherwise that's as bad an idea on a street car as running fixed ignition timing...

Although,

I had the same thing happen on my SBC although it didn't actually boil over, the warm up temp jumped drastically till the radiator got up to the same temp ad the engine.
I took the stat out and verified that it did open at 180º although like somone said, it was still completely closed at 179º and sorta jumped open, like th temp fluctuations do.
I cured it with a 1/8" diameter byp*** hole in the stat. That's about 3 times the area and flow volume of the .060" one you drilled.
Try a bigger hole.
Only drawback is when the air temp is below 60º the engine only gets up to about 165º but usually runs right at 182º

 

Have you re-checked your ign.timing? Just a thought.

 

timings dead on 8deg advance, i checked TDC and reset my pointer while i had my heads off too..