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Last Updated 11/16/07

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Thermostat Replacement

"Beating the Heat"

Symptoms of a Problem

Over the last few days I noticed a boiling/percolating sound coming from my
coolant tanks (pressure and swirl tanks). The tanks sat there vibrating as the
contents sounded like they were boiling, but I hadn't detected any fluids being discharged from the overflow hose. And, the temp gauge still showed consistent temperature readings, albeit with a few erratic swings of the needle (but no alarming temperatures reported).
 

Notes on my Cooling System

Last year I installed...

1. Brand new radiator - stock style copper/brass, no leaks

2. Weiand aluminum water pump

3. Rebuilt the stock cooling fans (with Cortina blades) - they work beautifully

4. A Tefba coolant filter - filter is clean, with no obstruction to flow

Additional notes...

1. Temperature sender was mounted in the water pump

2. Cooling system had been bled twice since the symptoms appeared - very little air

3. And, it didn't appear to be losing coolant - fluid level appeared constant

Anyway, I posted my dilemma to the DeTomaso E-Mail Forum and received a lot of questions and suggestions which helped me determine the best course of action to resolve the problem.

I picked up an infra-red temperature gun on my way home from work and checked temperatures at various points along the cooling system to determine if coolant temps were consistent throughout. They were not. It appeared the most likely culprit was a stuck thermostat due to the large temperature difference between the coolant bottle and the radiator, and the fact that once I removed the cap from the pressure tank it immediately boiled over. This led me to believe the coolant was merely circulating through the engine instead of through the radiator.

Correct 351 Cleveland Thermostats

The thermostat for a 351-Cleveland is different from the thermostat for a 351-Windsor. Either will fit in each engine, but the 351C thermostat has a copper "hat" that seals against a bypass restrictor plate inside the block, closing the bypass circuit when the thermostat opens, so that all coolant has to go through the radiator.

Those thermostats in the chart marked as "Cleveland specific" have been verified to be correct 351C thermostats with the hat to seal the bypass circuit in the block. I used a Stant #29468 thermostat because that's what was available from my local Kragens Auto Parts store. I also used a thin coat of Permatex #2 gasket sealer on the gasket surface to ensure a water-tight seal.

I have since learned that I didn't need the Cleveland-specific thermostat in my car, since my Weiand aluminum water pump does not have the bypass circuit. Therefore, if you have a Weiand aluminum water pump, you could use a standard Windsor thermostat, like the one I removed.

The Weiand 8209 water pump can be modified to add the bypass circuit:

http://pantera.infopop.cc/eve/forums/a/tpc/f/5650045562/m/6880012344?r=6880012344#6880012344

Temperature Sender Relocation

Panteras came from the factory with the temperature sender mounted in the side of the pressure tank rather than the engine. This is a poor location for the temp sender because it doesn't actually gauge engine temperature, and worse, if the car loses coolant the sender will only report the air temperature in the tank and not the temperature of the overheating engine. My car now has a drain petcock installed in the pressure tank in the original temp sender location. It allowed me to drain just the top of the cooling system so I could easily change the thermostat.

A previous owner of my car moved the temperature sender to the water pump, which is also a less-than-ideal location, because it sees cavitation off the pump impeller tips and temp readings from a bubble mix are bound to be non-linear. Therefore, I decided it was time to relocate the temperature sender from the water pump to the correct location in the block, directly beneath the thermostat. There's a 1/2" pipe plug there already, so it was merely a matter of moving the pipe plug to the water pump and moving the temp sender to the block.

In the picture above you can see the temp sender is now mounted in the block above the water pump and directly beneath the thermostat. This location will yield the most accurate and consistent temperature readings.

The temperature readings before and after the new thermostat was installed can be seen in the chart.

* All 'before' temps taken 15-20 minutes after shutdown - time required to open the IR Temp gun package, install battery and begin using it.

**  Reading taken 2.5-3 hours after shut down.

*** Reading taken while engine was running - Veglia gauge displayed 160.

Summary

There's no more boiling coolant in the pressure tank. All overheating symptoms are gone! And, my stock Veglia temp gauge appears to be spot-on (within 2-3 degrees). From a cold start, the gauge climbs to about 180, then drops back down near 90, then climbs back up, and goes through this cycle several times until the coolant temperature is equalized throughout the system.

Now I just need to get used to the higher gauge readings since I went from a 160-degree thermostat to a 180-degree thermostat. When my gauge used to register only 160-degrees, I doubted its accuracy fearing that it read low. However, its performance is consistent with what it used to be, but at 180-degrees now rather than 160-degrees. And, I've verified it with the IR temp gun. One more thing; I also backed off the timing advance by 2-3-degrees to avoid engine knock.