Hot Head - Transmission Digest

Hot Head

A 2000 Mercury Grand Marquis with a 4.6L engine using a 4R70W transmission is at a general-repair shop for weeks. The problem is an intermittent engine surge on top of the 1-2 shift when hot. The perception is an engine problem. Eventually, the idea of the converter clutch coming on was being considered. Without much testing, the valve body and solenoids were replaced yet the problem persisted.
Hot Head

Shift Pointers

Author: Wayne Colonna
Subject Matter: 4R70W Transmission
Issue: Cylinder head temperature

Shift Pointers

  • Author: Wayne Colonna
  • Subject Matter: 4R70W Transmission
  • Issue: Cylinder head temperature

A 2000 Mercury Grand Marquis with a 4.6L engine using a 4R70W transmission is at a general-repair shop for weeks. The problem is an intermittent engine surge on top of the 1-2 shift when hot. The perception is an engine problem. Eventually, the idea of the converter clutch coming on was being considered. Without much testing, the valve body and solenoids were replaced yet the problem persisted.

This shop had no knowledge of an ATSG bulletin that covers a similar problem. The bulletin speaks of the converter clutch applying on top of the 1-2 shift due to a deteriorated No. 7 check ball. The difference is the deteriorated No. 7 check ball causes the problem to occur on every 1-2 shift, cold or hot. The general-repair shop was fighting an intermittent 1-2 surge problem when hot. And it continued to have the same problem after changing the valve body and solenoids. After much frustration, he sent the vehicle to a local transmission shop to look into the problem.

Lorenzo Ortiz from Phillips Transmissions was the lucky one to receive this vehicle. After road testing the vehicle to experience the problem, it did indeed feel like the converter clutch was applying on the 1-2 shift. His first approach was to monitor the solenoid command with a scan tool and a volt meter. By doing this, he confirmed that the computer was indeed commanding the clutch to apply. The question now is why. With shift scheduling operating properly, engine load and vehicle speed could not be the problem. This narrowed the search down to temperature. The engine temperature and transmission fluid temperature were looked at and were text book perfect.

But Lorenzo noticed how the fans were running at full speed. He then looked at the cylinder head temperature (CHT) sensor and it was running at 262°F. He popped open the hood and ran the engine idle up to about 2,000 rpms for more than 30 seconds and watched the cylinder-head temp drop to almost engine-coolant temp.

Once the temperature dropped, the fans started to run normally and the converter clutch no longer applied on the 1-2 shift. As he drove the vehicle, the cylinder head was quite lethargic in increasing in temperature.
But with continued driving, the problem suddenly returned. Looking at the cylinder head temperature, he saw 251°F. Once again, by increasing engine rpms in park, the temperature would drop immediately. This confirmed that a flow problem existed with the engine coolant, causing a hot head. It also confirmed that the CHT sensor influences a converter clutch apply strategy that is not mentioned by Ford with this particular vehicle. It does state the following:

If the CHT exceeds about 121°C (250°F), the powertrain control module disables four fuel injectors at a time. The powertrain control module will alternate which fuel injectors are disabled every 32 engine cycles. The four cylinders that are not being fuel injected act as air pumps to aid in cooling the engine.

If the temperature exceeds about 166°C (330.8 F), the powertrain control module disables all of the fuel injectors until the engine temperature drops below approximately 154°C (309.2°F).

Since the engine coolant temperature was functioning normally, a defective water pump is not suspected. A restricted water jacket seemed more likely, which may be remedied with a flush. Lorenzo immediately returned the vehicle to the general-repair facility for them to resolve the flow problem as he heard the owner had a hot head waiting for his car.

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