When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hey everyone - Need a little help on this one....I've researched most of the threads, and have implemented a lot of the suggestions; but still have a problem....It's gotten a LOT better, but still not there....I'll try and be as detailed as possible to help the diagnosis...
Powertrain - 1986 L98 modified for track use - ZZ4 Cam; headers; aluminum heads; TPIS intake; custom tune for cam/heads setup...700R4 automatic with 2800 stall converter modified for drag racing...I've owned it for ~ 2yrs; the previous owner used it for drag racing....
Problem description - From purchase; the car would initially run at ~~ 210 around town and maybe 220 on the highway for about 20 minutes; then with extended use around town or highway the temps would start creeping up to 240 and beyond (loses control)...With the A/C on it was even worse..
ORIGINAL COOLING SETUP - Custom brass performance radiator single row of unknown brand; OEM cooling fan with on temp modified to 180 degrees. 160 degree thermostat.
Based on the recommendations from other threads; and my own troubleshooting; here's what I've done...
1) Replaced radiator with champion aluminum 2-row unit
2) Bypassed heater core and looped coolant from water pump back to intake (I noticed there was a leak at the automatic shut-off valve near the firewall)
3) Flushed the coolant system 4 times myself plus took it to a service station for professional flush.....Please note the coolant is a rusty color and I cannot get rid of it - Previous owner must have run straight water
4) Removed the A/C system and condenser...(Thought condenser may have been blocking airflow)
5) Installed high flow performance thermostat - Went to 180 degrees in an attempt to keep the coolant in the radiator longer for cooling.
6) The water pump had been replaced ~~ 8 yrs ago
Here's my current symptoms:
Upon initial start-up and driving around town...Once the system gets to temperature and thermostat opens - The temperature "oscillates" between 182 degrees and 192 degrees. In town; as long as I'm not getting on it; it will continue to oscillate in control of the temperature...Then - If I either start getting on it; or I drive it on the freeway for an extended period (> 30 minutes) here's what happens...1st the oscillation will stop and it will settle in around 186 degrees...After that the temperature slowly starts climbing and keeps going until it's out of control (>240) again.....
In my mind - It seems like the cooling has improved as under normal driving conditions/limited HWY use it keeps things under control; and with it "oscillating" I think I've got "enough radiator" to cool it down....I was thinking about replacing the water pump as it's the only thing left; but if that were it; I would think it wouldn't be able to control the temperature at all...I just don't know why it loses it over time; that seems like the key factor now...
My only wild *** guess would be the thermostat is sticking. I am not a giant advocate of the 160 stat. Are you sure you are getting to full pressure? Have you done a pressure test and see how it holds?
Dan
Do you have cooling fans? Are they working? The 86 was built with a 195 degree thermostat. It should never get to 240 degrees as the cooling fans are programmed to come on at 224 and generally do a great job of bringing the temp down.
Yes, do a pressure test. It is free. You can borrow the tester from auto parts stores. See if it holds pressure. I am somewhat of a nut but I always test my new thermostats in a pot of boiling water. I have found large changes in different stats. I compared a 190 AC Delco to a 190 fail safe. Both opened at 190 but at 198 the fail safe was full open while the AC Delco was open maybe 25%. Huge difference how they operate in real life. Thermostats should be rated by two numbers. One where it starts to open and one when it is fully open. I use the fail safe. Dan
You guys may be on to somethIng regarding flow….When I put in my heater bypass loop; I noticed that the original hose was caked up at the water pump connection with the brown rust material…To the point where a 3/4 (or 5/8 I can’t remember) hose was necked down to a 1/4 “ hole….
the fact that I can’t get rid of that brown stuff (rust) is bothering me….I wonder if I’ve got similar “caking” issues elsewhere in the passages and therefore creating either restriction in flow or inefficient heat transfer…..
Impellers can rust away, symptoms are ok idle temps but over heating above idle wither you're going down the road or fans are on. This picture is the worst one, but even half way gone impellers will move some coolant, just not enough.
i gave it multiple vinegar doses. full strength. drained the ks and pulled the kc4 cooler line from block to drain.
you might have a system full of stop leak!!!
Flush the system best you can. Take off lower radiator hose and rig up a garden hose to it....then take upper radiator hose and go right to the ground with it. Run engine till its puking clear water, then take out KS and block drain on other side and see what comes out. There should be nothing in those holes and should drain quickly....boats have that issue where that part of block will hold sand, making half the block not getting water. On a car its rust, and junk from decades of use.
Is the air dam in place and plug the heater core outlet so it does not bypass. You may want to drill a 1/8 hole in the thermostat to allow some water to pass and open up the thermostat.
I noticed that the original hose was caked up at the water pump connection with the brown rust material…To the point where a 3/4 (or 5/8 I can’t remember) hose was necked down to a 1/4 “ hole….
the fact that I can’t get rid of that brown stuff (rust) is bothering me….
Originally Posted by FostersPerformance
Flush the system best you can.
"I can't get rid of that brown stuff" ....sign of lack of cooling system maintenance, and evidence that you need to flush. I pull KS's, plumb garden hose to heater core hose that runs to the core then back to intake. Then, in one step, you're flushing the CORE (often overlooked), intake, heads block.
I used the Thermocure product (made by the Evaporust folks) on a '94 LT-1. It converts rust to a black powder and leaves shiny iron and steel behind. No foolin' dropped temps on the LT-1 25F. I wouldn't flush any other way now. Safer for your heater core than running acid through the system (i.e., vinegar). I did a thorough flush though, including lots of driving and pulling the block drains (which happen to be the knock detectors on an LT-1). You have to drain the anti-freeze and then run the Thermocure with water in the system for a period of time. Your coolant will turn black. No harm in leaving it in for an extended period and running the car a bunch prior to flushing it out as there's no cold weather in sight.
Product used to be available at most retailers, but I find I have to order it now. I think it wasn't that popular due to cost -- ~$30 per bottle. But, dang, it works.
So, this sounds like you have a flow/capacity issue. (based just on reading what you have written).
Usually with cooling, we want to check: Is it low speed or high speed issues? If low speed is hot, but driving is cool, then you usually have a fan airflow issue. If low speed is OK-ish but driving is hot, then you usually have a cooling capacity / water flow issue.
So here it looks like city driving is working at least someone correct. If you have a 180 degree t-stat, then your 182-192 range seems at least reasonable for how the t-stat actually works. Although once you get things set up right, setting your fan to come on more like 195 to 205 or something is more where your target will be, most likely. You want to be able to cruise steady state with the fan off.
With your radiator upgrade, let's assume the radiator capacity is OK
With your issue occurring at cruise speed, let's assume there is enough airflow (verify your fan direction, and no trash in the way, and your shrouds/air dams are in good shape)
Water flow and heat transfer to water seem still the suspect areas. The tips above about something more aggressive than just water flushing, and pulling/inspecting/replacing the water pump seem like reasonably easy tasks to do.
One other area might be: how is your tune/timing? Its a long shot, but poor tuning can lead to overheating also. If the timing is retarded, the spark, and therefore ignition occurs late. Normally, the expansion of combustion gasses cool them also (Charles's law). If the burn occurs more on the pistons way down, the heat ends up staying in the cylinder/walls and being transferred to the cooling system.
I have an 86, but I also have a C3, and we frequently deal with overheating issues in that forum. One thing that I did not see mentioned that you should check is your lower radiator hose. On the C3, they inserted a spring to stop the hoses from contracting. I can't remember if my 86 had/has one as well, but even if it did not from the factory, check the hose. Older hoses that feel 'squishy' can contract under the suction of the water pump, constricting flow and limiting the capacity to cool. If your hose feels soft, replace with a quality part.
What's so odd to me is that you mention that the temp rises on the highway. At highway speed, you shouldn't need any fans to help in cooling at all. If you have the front chin spoilers in place, the force of the air at that speed should be enough to keep it cool. I see a previous poster asked the question but can't find whether or not it was answered. In the C3 world, that chin spoiler/air dam is a vital part of the cooling system, as is making sure that any/all seals around the radiator are in place and working.
What's so odd to me is that you mention that the temp rises on the highway. At highway speed, you shouldn't need any fans to help in cooling at all. If you have the front chin spoilers in place, the force of the air at that speed should be enough to keep it cool. I see a previous poster asked the question but can't find whether or not it was answered. In the C3 world, that chin spoiler/air dam is a vital part of the cooling system, as is making sure that any/all seals around the radiator are in place and working.
because of this exact circumstance i think its a coolant flow rate issue not an air flow issue.
system either blocked.plugged or waterpump not pumping. my guess
We had Gordon Killebrew visit our club for a tech day several years ago. Long story short, early C4’s are notorious for accumulating a lot debris behind the air dam and air flow is cut off. Might be a more complicated problem, but put the car on a lift and check from underneath. It’s difficult to get to, that’s why so much stuff can accumulate there.
'86 overheating problem - What else can I try??
