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Unusual Over Heating Problem

3634 Views 16 Replies 8 Participants Last post by  Camaro_fever68
I have a unusual over heating problem. Runs cool at idle, hot cruising. Pull the thermostat and it won't get over 160 degrees. Put a 180 thermostat back in it and it won't keep a low temp at cruise.
This problem just started. Been running fine for a year or so. I have a Griffen aluminum radiator and Edelbrock high flow water pump that was freshly overhauled by Edelbrock a year ago. I have been running a "regular" thermostat for a year. I replaced it with a regular t-stat and now it's doing the same thing. I just ordered a high flow Stewarts Components modified Robert Shaw t-stat to try in it.
What I don't get is it has been fine with a regular t-stat, why would it all of sudden need a high flow stat? Could the water pump impeller be spinning on the shaft or something? How and where do you plum in to check water pressure output of the pump, What would be the procedure? It's a SBC long water pump. One heater hose comes off the intake and the other goes to the pump.

Edit: Forgot to mention my temp gauge jumps all over the place like what happens when the water is low in radiator. It'll jump to 240 degrees and then come back down. Doesn't do any of that without a thermostat.
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Have you tried a manual temp gauge to check the other? Or a infrared surface temp gauge. Perhaps the guage in the car is bad or poorly grounded. PErhaps you have pockets of air trapped in the coolant system. Tried running the car at idle dead cold till thermostat opens with radiator cap off? Turn on the heater also. Be surprised how much air can get trapped in a cooling system. Only other thing that I thought of. First engine I built overheated at speed on the highway. Even got warm in town. Allways cooled down at a idle or slowing down / engine braking. Figured out flex fans are junk. Just a few ideas. Hope this helps. Good luck.
I can only think of 2 things -

First, you may still have air pockets in the engine.

Second, you NEED a high-flow stat like the one you ordered, because of your pump.
I did shoot it with a IR gun. I don't have a cooling fan or radiator problem. I've got a 70+ degree drop in temp across the radiator from one side to the other with the fans on high. I let it run without the cap on until the stat opened. I topped it off and then brought the engine up to 2500 rpm and topped it off again then replaced the cap before letting the rpm back down.

I got bypass holes drilled in my stat. After driving it I came back home and killed the engine, turned on the fans and cooled off the radiator. Once cool I pulled the cap and it was full. Aggravated, I pulled the stat again, refilled the radiator, and drove it again. In 40 degree weather it won't come off 100* mark unless I turn off my fans at idle. Heater is COLD too!!

I guess my pump is working right. Must be the that the standard t-stat can't flow enough water to keep up with the pump. I always did notice that during a WOT run it would heat up but then was cooled back down on the return road. Probably always did need the hi-flow stat.

Thanks guys
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I'm trying to solve my problem which is similar to whats been said so rather than post a new topic, maybe you guys can comment on my problem.

When I'm driving on the freeway, my 71 Ec seems to get hotter than when it is idling. Would this be because of my stat, a collapsing hose at high speed, or a bad water pump? I'm running a stock thermo fan with shroud, stock 307 w/ no AC, automatic. It will usually stay at around 160-180, but gets up to 190-200 on the freeway and that is with a 65 degree outside temp. I'd like to resolve the issue before the weather gets hot.
Several possibilities - let's assume it's been this way a while and you haven't recently changed anything.

This is either a coolant flow problem or airflow problem, likely airflow. Could be your radiator isn't up to the task while the engine is making heat (cruising) but is OK when at idle.

Could be coolant flow - collapsed hose as you suggest, or a thermostat that's not opening all the way, or a thermostat that's NOT high-flow while your water pump IS.

If you're pump itself is going bad (some of the cheaper impellers will corrode quickly and won't flow much fluid) it's also a possibility, but I would think not.

If I had to bet, I'd go with an old radiator that's no longer up to the task. You may get lucky with just a real good flush and refill, but for a 307 a cheap 2-core radiator or having yours recored may be the ticket.
Thanks Mark. As I thought, sounds like I need to take each step one at a time. I haven't had the EC for very long so I'm unaware of what it's history is.
I had a simular problem check the rad mine was warm with a good temp drop but the bottom third was cold as Ice, you would think if the rad was blocked it would run hot mine ran cool until loads at highway speeds just started out of the blue. ALuminum rad especially start getting electrolisist build up from a possible bad ground.
Well, tried the Stewarts modified Robert Shaw high flow t-stat and it did the same thing the regular t-stats did. I pulled it back out and it runs fine without it, just too cold.

I don't know what is wrong with this system.
I'd bet on the collapsed hose. Easy to check. After the engine is up to temp ...making the hose softer, watch the hoses as you have someone increase the RPM's.

Seen it happen before, and easy to fix. It doesn't hurt to have extra hoses around anyway, and hoses are relatively cheap. Just make sure they have a spring inside to help avoid the collapse.
If your system runs cold with no thermostat and too hot WITH a thermostat I'd put my money on the problem being with the thermostat. Make sure that the stsat is installed in the proper direction. I'm not trying to insult toyr intelligence but I'v done it myself. Duh. Also, I would not rule out multiple sticking thermostats. You can get brand new ones that stick. New doesn't alwayys mean good. Dangle the thermostat in a pan of hot water. Use a dial thermometer or infrared thermometer to check the water temp. Don't let the stat touch the bottom of the pan or it will pick up a higher temp from the flame. When installing the stat make sure the sensing element is toward the engine side. I always drill an 1/8" hole in the outer housing so that filling is easier. The hole will eliminate the possibility of an air pocket building below the stat and let the air vent out through the top when you are filling. It also provides a small bypass if you have blocked off the original one. Please let us know how you resolve this problem. Overheating problems seem to be the most mysterious of all problems. The solutions and troubleshooting also seems to be the most untechnical and unscientific. Almost on par with parts changing solutions. A lot needs to be done with the science of water and airflow as it relates to automobiles. I have worked with thermodynamic problems most of my life, but when it comes to the automotive industry, there almost is no specifications for water flow or air flow. The closest you can get is a high flow vs a normal flow water pump. I'v seen some electric pumps rated in gpm. That is not a specification. A pump needs to be rated in flow @ a given pressur or usually @ low pressur suck as inches of water or feet of water head. The same with air flow. Fans are rated not in CFM, but CFM at a given pressure. Again usually inches of water. A 17" fan turning at 1500 rpm will move a lot more air through a single pass radiator than through a four pass radiator. The same goes for radiators. What the heck is a heavy duty radiator? It's whatever you want it to be. Any heat exchanger and most all except radistors and trans coolers are rated on the liquid side and the air side. Example: A hot water heating coil will have a rating such as: water temp in 180 deg, water temp out 169 deg. water flow 5 gpm. air flow 1000 cfm @ 3 inches of water. Compare that spec to a racing heavy duty radiato or water pump. This is not rocket science. That heating coil that I described could be for comfort heating in an office buildinf or in your garage, The same thing goes for transmission coolers. Ask someone what the ideal temperature should be comming out of the cooler. The usually have no temperature gauge let alone any kind of control. Try to find out if you should abandone the original cooler when installing an aftermarket and you will get three answers. 1. abandon the original. 2 Install the new one before the original. 3. Install the new one after the original. Usually the advise is given without recommending a temperature gauge to monitor what is going on.
Getting back to the cooling system.. how many BTU's are we trying to get from the cooling water? The solution to cooling problems can be solved easily. But first you need to know the facts. Hoe many horsepower does it take to drive a normal water pump? 1, 5, 10? I don't have a clue, bur I do know that the more water you move with a pump the more horsepower it requires. I'm not convinced that moving more water through a cooling system is the answer to better cooling.
If you could just measure the amount of water going to your radiator, you would be well on your way to solving a lot of these problems. It's easy to get the in and out temperatures of the radiator with an infrared gun. An oriface could be designed to measure water flow. This is really the missing ling. Water flow monitor. For racing applications, a processor could monitor water floe, system pressures, temps, aand control an electric radiator fan and an electric water pump fpr optimum horsepower reduction and thermal efficiency.
After being out of the high performance field and comming back after many years I was amazed at the advancement of technology in heads, camshafts, valve geometry, piston pin offset. and I could go on and on. The cooling system for the exception of some parts being cheaper like the aluminum radiator is no different than they were 20 years ago. Everything is hit and miss. Oh, you're overheating, change your 17 inch fan to a 19 inch. Oh, that didn't work, change your 4 pass copper radiator to a 2 pass aluminum. No better? Well I know a guy who used a hi flow water pump, yadda yadda yadda. Don't shoot the messenger.:eek:
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New hoses, more thermostats, checked thermostats in a pan of hot water.....still can't figure out the problem.

I'm still trying to figure out why my car won't hold the right temp with a thermostat. I'm running a Robert Shaw, Steward modified hi-flow 180 degree thermostat. It does all sorts of crazy things with a thermostat in.

1. Sometimes when I first crank it and let it warm up, the temp will come up slow, get close to the normal operating temp and the needle will suddenly swing wild jumping from 170 to 220, 240, and then settle back down to the operating temp and stay there.

2. Sometimes cruising down the road, temperature normal, let off the gas coming to a stop light or a stop, the needle swings crazy again getting real hot, radiator/engine has a popping noise like water boiling, put it in neutral and raise the engine speed and it will cool off again.

3. Sometimes it gets crazy with the running hot and water boiling at low speed, sometimes it does it at cruise speeds.

It's not the gauge, I changed it. It's not the thermostat, I tried a few and did the pan of hot water test. It's not the hoses, they are new.

Without a thermostat, it runs fine. Stays too cold while cruising. Engine doesn't run as good cold.

I got Brodix aluminum heads and a Victor Jr. intake. I've run aluminum heads before without incidents but I'm doing some deep off the wall thinking now. Could my heads not be flowing enough water since it has to come from the back. The thermostat can't react quick enough to differences in water flow like when I let off the gas and the water in the back of the heads gets hot. Maybe I need the water bypass kit. I'd have to drill and tap the intake for that.
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It's odd for the temp to jump around like that. Are you sure all the air is out of the system?

Got any pics of your engine compartment/hose setup?
what kind of gauge?? stock / electric after market / manual after market ?? could it be the sending wire is grounding out causing the bounce ... are you sure the sending unit is good ?? have you checked your ground wires ?? bad grounds cause erratic readings on gauges
The gauge is a mechanical aftermarket. The car is grounded real good. Body to engine, frame to engine, engine to battery.

The Robert Shaw hi-flow thermostats are modified by Stewart with (3) 3/16" holes drilled for bypasses. I enlarged these three holes to 1/4" and it works right!!!

I don't really know why enlarging those three holes made such a big difference. I know it has an effect on the cycling process.
Don't blow off the ground because the CAR/Engine is well-grounded. What about the ground for the gauge inside the car? Check the tightness of the connection at the gauge and whatever the gauge is grounded to.

Might be a silly question, but is your thermostat mounted upside-down by any chance?
Don't blow off the ground because the CAR/Engine is well-grounded. What about the ground for the gauge inside the car? Check the tightness of the connection at the gauge and whatever the gauge is grounded to.

Might be a silly question, but is your thermostat mounted upside-down by any chance?

The gauge has no ground. It has a capillary that goes into the intake manifold. The only ground is for the light bulb.

Not a silly question as some people do not know how a thermostat should go. I have ASE certs (expired) and once upon a time was pullin wrenches at shops. It's not upside down.

This is what I think my main problem is:

External PlumbingStreet-driven vehicles seldom need auxiliary plumbing or coolant lines. SBC race engines with aluminum cylinder heads usually require extensive external plumbing to address two design problems:

1.Aluminum heads have much smaller water jackets than cast-iron heads because the external dimensions are similar, but the ports are usually larger, the deck is thicker, and the material near the rocker stands is thicker, all leaving less area in the water jackets. This decreased internal area leaves less area in the water jackets.2.The siamese center exhaust ports are a design compromise that presents additional problems when aluminum heads are used. The area near the center exhaust valves is thicker, thus allowing providing less surface area for cooling.
We recommend installing a pair of –10 AN lines that connect the rear of the aluminum cylinder heads to the thermostat housing crossover in the front. This step will help offset the smaller water jackets. A pair of -10AN lines connecting the pressure side of the water pump with the area in the center of the cylinder head (just below the exhaust ports) will offset the lack of surface area due to the extra material.
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