mallisonb

I have a '85 Chevy Caprice, 4.3L V6. In reading many of the threads on overheating, I would have never imagined that the problem of overheating was so complex. There are 420 threads with the keyword overheating in them (not all related to the cooling system) and I've read a number of them, but I just couldn't bring myself to scan through that many to see which ones might be relevant to my case. I'll be as concise as possible.



Problem started when I could smell my engine overheating but indicator light was not working (don't have temp gauge). Cooling system was also losing fluid. Prior to this my mechanic told me there was a leak somewhere in cooling system so he added some stop leak and told me to check fluid levels regularly. I took that to mean that the leak was either not repairable or would be very expensive to repair. Long story short.

• Added second dose of stop leak (probably a mistake) - didn't seem to help.
• Discovered failed water pump - replaced it, stopped loosing fluid
• Replaced tstat at the same time as water pump.
• Installed new temp sending unit - temp indicator light started working
• Flushed system using a flushing agent and flushing kit (the one where you install the access port into the heater hose and hook up the water hose). - Recovered some sediment but didn't seem to be excessive.
• Recently replaced ruptured top hose on radiator (due to ~6-8 inch split).
• Disconnected ingoing and outgoing heater hoses,hooked up water hose and ran water through heater core - water flowed fine, no blockage there.
• At the same time, I applied vacuum to the heater control valve - water flow shut off, so valve is working fine.
• As far as the indicator light goes, it takes a while for it to start showing red and it gets slowly brighter with time. Having the heater on doesn't seem to dim the indicator light and having the A/C on doesn't seem to brighten it. Also, it seems that when I first head out in the morning, I can smell the engine overheating but the light is not registering that and the smell goes away after a while, so I'm not sure the temperature sending unit is accurately representing what is going on in the cooling system.
• Tested (by feel) temperature on various hoses under different conditions.
  • When heater is running, both heater hoses are hot as blue blazes, top radiator hose is almost as hot and bottom radiator hose is a little hot but not real hot.
  • When heater is off or the A/C on, both heater hoses are warm or cool and two radiator hoses are about the same as before.

I haven't noticed any change in cooling fluid (except I think the antifreeze is getting toasted) or engine oil; nor have I noticed any changes in power that would suggest a blown head gasket or warped head. I'm thinking the cooling system on this car is much more primative than on cars built in the last 10 to 20 years and the problem should be easier to figure out than in some of the threads I've read. My suspiscion is that I've clogged the radiator with the stop leak, but I haven't ruled out the possiblity of an obstruction in the engine block.

Any thoughts?
Thanks

kevinkpk

History. Has the radiator been recored, or fixed due to external damage? Is the cooling fan turning, is it a thermo controlled fan? Is the water pump correct for an air conditioned unit?

mallisonb

Thanks for your response. Update so far.

1. The radiator has not been recored or repaired as far as I know. I do think it has been replaced before I got the car. I can find out but haven't yet.
2. The cooling fan does work and is supposed to be thermo controlled. Next to the thermostat, there is a temp sensor that communicates with the ECM which in turn is supposed to control the fan clutch. I'm not sure either the sensor or clutch is functioning correctly. Preliminary tests show that the temp sensor does not exhibit the range of ohms that it should. When cold, its supposed to be somewhere around 35K ohms. When hot, its supposed to be below 200 ohms. In preliminary tests, I get from about 2000 (cold) to 195 (hot). I haven't gotten any error codes to indicate the temp sensor is bad, but I may replace it since its easy to do. The fan clutch doesn't have any play in it but it doesn't seem to spin the way the repair manual says it should. Its supposed to spin with less resistance (engine off) when the engine is warm just after startup and more resistance when the engine is hot. It seems to show the same resistance (about 1/2 revolution) whether hot or cold. Auto parts stores say to replace clutch when replacing water pump. Don't know if thats valid advice or just marketing lanquage. In any event, I haven't replaced it since I've had the car. What's your experience with fan clutches?
3. Water pump is standard duty. I checked web sites for the major auto parts stores and none associate a particular model with an A/C equiped car. They specify standard duty and heavy duty. So to answer your question about the water pump, I don't know, but I suppose its not much of a logical leap to assume that I need the heavy duty water pump. Is that your read?

Now, things I found out in checking out these other issues.

1. Coolant recovery tank is not filling up when engine gets hot. I assume the radiator cap is bad and its no big deal to replace it.
2. When I squeeze the upper radiator hose while the engine is running at hot, I do not feel the surge upon release. Does this necessarily mean the water pump isn't pumping or can it also mean that there is an obstruction someplace that is preventing flow?
3. Correction on initial post. The heater hoses are very hot regardless of whether the A/C is on or heater is on. (don't know if this changes anything).

kapriceblizz

thermostat and water pump . replace both and you will be fine

mallisonb

Kevinkpk & Kapriceblizz, thanks for the input. If you are still with me, here is where things stand. I addressed all the issues you both raised and its better but I still have a overheating problem. These are the things I did. I flushed the radiator and decided later that I should have flushed the entire cooling system, which I did a week or so later. Both times, I got a lot a rust and sediment out. That seemed to help the most but didn't completely fix the problem. When I flushed the entire system, I took the opportunity to remove the water pump and thermostate. Both are practically brand new, not more than 5-6 months old and both checked out fine. Regarding the issue of whether the water pump was the right one for a car with AC, I contacted the manufacturer and they said that AC doesn't matter; you only need a heavy duty water pump if you are hauling a heavy load or driving in mountainous terrain. I checked out the fan clutch next. It was a standard duty thermal fan clutch rated for a fan with 1.5 inch pitch. My fan has 2.5 inch pitch so I upgraded to a heavy duty thermal fan clutch. Makes my V6 sound like a V8 but otherwise doesn't seem to effect the overheating issue. My next thought was that there was really nothing wrong with the engine but the temperature sending unit was the wrong one. That was the first part I replaced months ago, but its the only one I could buy locally and it supposed to be rated to close at 210 degrees. I'm still waiting to hear from the radiator manufacturer on what kind of termperatures I can expect for a car of my vintage. I don't think they are going to respond. I also checked the pressure in the upper radiator hose and it never went above 16 psi, which is what the radiator cap is rated at. So having done all that, I've narrowed it down to two possible causes. One is that there is a stubborn radiator clog that is causing a cold spot and preventing adequate cooling. As far as I know, the only way to definitively verify that is to us a thermal scanner. However, for the price of having that done, I could probably buy a new radiator. The second possible cause is that there is hot gasses leaking through the head gasket. I'm leaning toward this theory because in the three times I've flushed the cooling system over the last 5 to 6 months, I've noticed an oil sheen on the coolant. The first time there was heavy sheen; the other two times, just a very slight sheen. I haven't noticed any water in the oil though. I noticed that the auto parts stores carry an additive for plugging leaks in head gaskets. I was thinking about trying it but I'm always dubious of any leak plugging additives. Is there anyone out there that has tried this stuff and can say whether it works or not? Thanks.