Over heating Spider

[marka206]

Help! I can't seem to correct the overheating problem with my 1981 FIAT spider.I bought the car as a garage find last April, and it had been sitting since 2003. I drained the coolant from the radiator and block, flushed them both , installed new thermostat & hoses, and was careful to refill the coolant as per shop manual instructions. The car has the prestone tee fitting on the high point of the heater line above the exhaust cam tower, so I made sure that it and the line to the fuel injection was filled. After about four miles the temp gauge was bumping the red zone, followed by it pegging half a minute later. The electric fan only turns on when the temp is very far into the red. The thermostat seemed to be open as the lower radiator hose was hot,and I took the precaution of drilling a small 3/32 hole in the thermostat plate . The records indicate that the water pump was replaced about 10,000 miles ago, so I left it alone. I'm thinking of replacing the fan thermostat next. The car was overheating before I started all this.
I welcome your suggestions on how to correct this problem so I can get my little spider back on the road. Mark

[bobplyler]

Are you sure the thermostat is installed correctly? It's real easy to get wrong.

[kmac33]

I would be willing to bet you haven't gotten the system completely "burped". There are a few previous threads that detail the most effective method to ensure the system is as "air free" as possible. Did you "burp" the system with the heater valve open and closed? Even with the T fitting, I'd have the car sitting up on an incline to help the process.
Took me 2 attempts at burping my system to get it air free.

[So Cal Mark]

if the lower hose is hot, the stat should be open. Have you checked across the surface of the radiator for cold spots that would indicate a restricted radiator?

[courtenay]

I had a similar problem on my '80. It turned out that the problem was the temp sensor in the block that pegs the needle was faulty. Based on some advice from others on the forum, I disconnected this sensor and all is fine now. Before doing this, I did all the usual stuff on burping the system, replacing the t-stat etc and used an infrared thermostat to check the temperatures of the rad, hoses and block. If you do a search on my posts you can find out more.

[Exit98]

Marka,

Yeah, what Courtenay said.

I don't think the car is overheating at all. I think one of the two sensors in the head between the cam covers is loose or coroded, Pull up the covers and clean up and tighten the contact points.

I've still got some little problem there dispite my efforts and from time to time the gauge pegs. Open the hood, fool around with the wire, all's good.

Let us know.

[marka206]

Are you sure the thermostat is installed correctly? It's real easy to get wrong.

The thermostat I installed had one leg labeled radiator ( that went to the lower radiator nipple) , and another labeled motor ( that went to the tee fitting on the front of the engine), the third went to the water pump. It looked the same as in the shop manual.

[marka206]

I would be willing to bet you haven't gotten the system completely "burped". There are a few previous threads that detail the most effective method to ensure the system is as "air free" as possible. Did you "burp" the system with the heater valve open and closed? Even with the T fitting, I'd have the car sitting up on an incline to help the process.
Took me 2 attempts at burping my system to get it air free.

I'm going to try it again on an incline this time. yes I had the heater valve open. Thanks for the suggestion......Mark

[marka206]

if the lower hose is hot, the stat should be open. Have you checked across the surface of the radiator for cold spots that would indicate a restricted radiator?

The radiator is a fairly recent rebuilt replacement by the former owner, and it looks pretty good........Mark

[marka206]

I had a similar problem on my '80. It turned out that the problem was the temp sensor in the block that pegs the needle was faulty. Based on some advice from others on the forum, I disconnected this sensor and all is fine now. Before doing this, I did all the usual stuff on burping the system, replacing the t-stat etc and used an infrared thermostat to check the temperatures of the rad, hoses and block. If you do a search on my posts you can find out more.

Thanks Bruce, If my second attempt at burping fails, I will look at the sensors.......Mark

[So Cal Mark]

it always helps to get ALL of the information to help solve a problem

[mattw]

I have a 78 spider. I had the same problem overheating. At first, it would only overheat occasionally. I went thru the usual stuff. Added the tee in the line to fill with,burped, jacked front end really high while filling, same results. Changed out thermostat 2 times, changed out bottom radiator sensor 3 times, changed out water pump, same problems. Then changed to the in head thermostat (with the bleeder hole drilled in thermostat) and done away with the external thermostat. Same problems. Every time burping, bleeding, raising front of car, checking for cold spots on bottom of radiator,etc.. So then I began to think about the temp sensor on the bottom of the radiator being on the opposite side of the radiator from the outlet side of the flow. That would mean that the majority of the water would never touch the sensor. So I fabricated a stainless tube (the size that would slip inside of the bottom radiator hose) and welded a bung in it to put a temp sensor in, cut the bottom radiator hose about half way up and installed the stainless tube with the temp sensor in it. Wired the temp sensor up in place of the original one, and now all the water that runs thru the radiator now passes by the sensor. It works great and works the same every time.

[So Cal Mark]

the main problem with relocating the sensor is that now you have placed it in the coolest spot in the cooling system. Generally the water temp will drop 15-25 degrees from the top of the radiator to the bottom, so with that sensor set at 195, your motor could reach 220 or so before the fan comes on. The sensor location in the bottom of the rad guarantees it will water around it all of the time unless your system is empty. The two problems I see with the bottom position is the possibility of a debris buildup around the sensor or restricted radiator tubes that limit flow. Either of those problems have to be dealt with for proper cooling though

[mattw]

You are correct that there will be a temperature difference in the main flow of water coming out of the bottom of the radiator hose. It's been over a year since I done this and forgot to mention that I placed a 3/8" NPT bung and used a temp sensor that I sourced from local auto store rated around 180 degrees. This allowed my fan to come on around 190 degrees consistently.

Matthew Weathers