Sudden high temp on gauge.

[DMC5180]

Please post a photo of your engine installation with good visuals of the hoses to the water pump.

Did you pull the pump to actually look at the impeller?

Also when the otterstat had the fan running did you physically feel the return line for noticeable temperature difference? I ask because I was surprised how much lower the return side is when the fans are running and the engine is idling. Low rpm water flow really allows the radiator/ fans to pull the heat out if the coolant.

In my case the otterstat side was to hot to touch while the return side felt like ambient temp.

[Timebender]

Last night, I ran the car again and it was still getting too hot - after running water through it with the hose on and in the radiator, putting water and some coolant in the engine before putting on the thermostat - which I drilled. So I shut it off for a bit to cool it down, and wondered if the plastic overflow was too full. So I removed it, and noticed the hose from the metal tank never was actually doing anything, as I had connected it directly to one of the nipples, assuming there was a hose inside connected as well.

NOPE.

So I got the hose inside the plastic tank out (which it came with and I never noticed), drilled a hole just a little smaller than the hose to fit tight, and then put the tank back in and connected the new clear hose to the metal tank, and followed that with filling it about 1/3rd.

Ran the car again, fan came on at around the 235 mark (which is actually about 220 -maybe less as it's a 180 degree otterstat) - and still got too hot.
So let it cool down again then put it back in the garage. But, I did notice a little green coming into the clear hose, with lots of air bubbles.

This morning I thought I'd run it again so more air would come out, and noticed the plastic tank was almost empty. So I filled it up about half way, fired up the D, and waited. It took longer than before to warm up (good), and then the fan came on just below the 220 mark, which is about 195, and stayed on for about 20 minutes as I watched the temp drop to 180 on the gauge - and the fan shut off. Took about 10 minutes to climb back up and just below 220 on the gauge, the fan came on. But this time it seemed to stay - never climbed, and I think I waited about 10 minutes but it didn't drop again either - which I think is somewhat normal.

After shutting off the car and going in the house, I did go back out and heard a blooping sound, to find that there was more air going into the plastic tank.

So overall it's a success.

But I would like to get the cap off the metal tank at some point and see if it needs to be filled more as well - however no matter how I try, it just doesn't want to come loose - either by twisting or pressing and twisting.

Any ideas would be appreciated, and I want to thank everyone who chipped in with advice and help!

[DMC5180]

Sounds like you just needed to work air out of the system. Do you know if there is a high point air bleeder on your radiator? I assume you have a custom radiator. On the OE radiator their is a bleed hose on the Passenger side which doesn't alway work like it should. You end up pulling the little hose loose just enough the let the air escape. One of the aftermarket suppliers actually incorporates a bleed screw on the top of the RH radiator end tank.

[opethmike]

Having owned a few mid and rear-engine cars, I can with good experience say that it is worth the money to get an Air Lift vacuum:

http://www.tooltopia.com/uview-55000...iABEgJnnPD_BwE

[Bitsyncmaster]

It's normal when the thermostat opens the coolant is flowing through the cold radiator and then the thermostat closes because of that cold return coolant. It keeps doing that with shorter cycles until the radiator heats up to normal temp.

The otterstat has about 8 deg. C of hysteresis which is about 15 deg. F

[Timebender]

It's normal when the thermostat opens the coolant is flowing through the cold radiator and then the thermostat closes because of that cold return coolant. It keeps doing that with shorter cycles until the radiator heats up to normal temp.

The otterstat has about 8 deg. C of hysteresis which is about 15 deg. F

Oh that's interesting and good to know!

[Timebender]

Sounds like you just needed to work air out of the system. Do you know if there is a high point air bleeder on your radiator? I assume you have a custom radiator. On the OE radiator their is a bleed hose on the Passenger side which doesn't alway work like it should. You end up pulling the little hose loose just enough the let the air escape. One of the aftermarket suppliers actually incorporates a bleed screw on the top of the RH radiator end tank.

Yep - amazing how much trouble that can cause. As far as the radiator, maybe? Or it's stock out of something bigger - the cap is on the passenger side at an angle between the top and side, so it makes it difficult to fill it "all the way" to the top, and fluid likes to spill out most anytime I take it off unless it's low.

And as far as the metal tank - I haven't found any bleed screw on it - seems to be sealed tight and still trying to figure out how to get the lid off.

[Timebender]

Having owned a few mid and rear-engine cars, I can with good experience say that it is worth the money to get an Air Lift vacuum:

http://www.tooltopia.com/uview-55000...iABEgJnnPD_BwE

Oh that's swanky.

[David T]

Oh that's swanky.

To use it you must have a large air compressor so you can pull a hard enough vacuum. It will only work on a system that is completely empty. You get one shot at it so you need to fill a bucket with 2 gallons of anti-freeze and 2 gallons of water and do it all in one shot. You should still pressurize the system afterwards and bleed any residual air out but it does work well. A very nice tool to have but not essential. You can do a proper job with just the pressure tester but it will take more time.

[Ron]

+1 on thermostat

The sensor is on the side of the block above close to the spark plugs.

It's probably not the problem, but the fan switch should be in the head, not on the side of the block. The correct port is between cylinders 6 & 8, a little higher than the spark plugs. (If the heads have been swapped, it's between 1 & 3 and OK.)
Check that a heavy duty connector (like OEM, usually has dark brown holder) is being used in any case, especially if it has headers!