Overheating on the highway. 76, 2.0 Options

[SVG223]

My 914 overheats on the highway. I had concerns about the air flap, but I think the thermostat has broken and it stays in the open position. I thought something might be clogging the fan but it looks clear. I wonder about the heater air hose that goes over the motor. It could be blocking some air possibly. I may try to tie it out of the way. After exiting the highway and stopping at a stopsign the idle was extremely low, I was surprised it was still running. I turned the engine off for a while and it ran better after it cooled down. Any ideas would be appreciated.

[Superhawk996]

Based on info above I'm more convinced that something isn't right. You should be able to run those speeds, at those ambient conditions all day long without issue.

First thing I would do is verify the part number on the oil temp sender. It's free and easy to do. This at least gets us to a baseline where we know about what temp you're oil really is.

I'm not suggesting that is the problem but it is one of symptoms that got your attention.

Next, I'd get a cheap boreoscope, Amazon, iphone app, whatever. They are pretty cheap.

Make sure you don't have the oil cooler plugged with debris or one of these situations (all 3 came from my own tear down core engines -- 3 of 3 had what would be fatal blockages if you tried to run like this):






Blocked oil coolers are amazingly common on these older cars and there isn't an easy way to clean them as annual maintenance. The rodent problems are very real for vehicles stored a good part of the year. Likewise, mice can build one of these nests very quickly - just a matter of a few days.

Next up: Verify timing and make sure you're not running with too much advance.

We haven't talked about what you're running carbs or fuel injection. Either way, you need to verify that the fuel system isn't running lean. This can be as basic as reading the spark plugs.

As previously mentioned by others a cylinder head temp gauge on Cylinder #3 is a real good thing to have since head temperatures lead oil temperatures by a wide time margin. By the time you see the oil temp going up, the heads have been hot for a long while.

[SVG223]

Based on info above I'm more convinced that something isn't right. You should be able to run those speeds, at those ambient conditions all day long without issue.

First thing I would do is verify the part number on the oil temp sender. It's free and easy to do. This at least gets us to a baseline where we know about what temp you're oil really is.

I'm not suggesting that is the problem but it is one of symptoms that got your attention.

Next, I'd get a cheap boreoscope, Amazon, iphone app, whatever. They are pretty cheap.

Make sure you don't have the oil cooler plugged with debris or one of these situations (all 3 came from my own tear down core engines -- 3 of 3 had what would be fatal blockages if you tried to run like this):






Blocked oil coolers are amazingly common on these older cars and there isn't an easy way to clean them as annual maintenance. The rodent problems are very real for vehicles stored a good part of the year. Likewise, mice can build one of these nests very quickly - just a matter of a few days.

Next up: Verify timing and make sure you're not running with too much advance.

We haven't talked about what you're running carbs or fuel injection. Either way, you need to verify that the fuel system isn't running lean. This can be as basic as reading the spark plugs.

As previously mentioned by others a cylinder head temp gauge on Cylinder #3 is a real good thing to have since head temperatures lead oil temperatures by a wide time margin. By the time you see the oil temp going up, the heads have been hot for a long while.

Thanks for these pictures they give me an idea of what could be happening. Stock D Jetronic. A head temp gauge would be nice, ideally, it would be a vdo gauge in place of the clock in the center console.