Engine thermal death due to fault in transmission oil cooler (automatic)?

[obenhaus]

Three years ago, shortly after Christmas, my 164 24V automatic broke down. After a drive through the villages, we hit the motorway. After a short drive at 140 km/h, the oil pressure light came on and the engine immediately lost power. Crank bearing damage, later it turned out to be piston seizure.

The repair was delayed. Last summer, the car with a PS Schulze rump engine went back on the road. Only in city traffic. On the first long journey, the thermometer tripped after a while and the indicator light came on. I then noticed on two journeys through the industrial zones: up to 1 hour it stands at 90 degrees, then suddenly the temperature rises until the red light comes on.

Since then, the car has been back in the workshop - due to lack of capacity.

The previously deceased engine was one that I had bought in the classifieds - for little money, from someone who had given up his project, as he said.

The engine ran for a few years, but only on the occasional short ride around Hamburg. It ran so far so good, only it had a noise like a piston tipper. It never got too hot.

The engine came in when the car was in storage after a previous engine failure after 2014. The previous engine ran out of power at some point, having travelled Hamburg-Zurich quite often before.

Yes, the engine worm is in there.

So I now fear that there is a deeper problem. The car had already been checked for temperature before the breakdown in 2014. But always without findings.

The new transmission cooler came in because I did a transmission flush. They said: we have to remove the hoses and someone once attached a hose to the radiator at an angle. So I got a used spare part from someone from this register and had it fitted by the Alfa workshop before the flushing was carried out.

Recently, the thought of the transmission oil cooler came up in conversation. It was replaced the year before the car broke down - with a spare part. The radiator has a fan on it.

[obenhaus]

The problems described indicate a complex combination of causes that could relate to both the engine and the cooling system. The most noticeable symptoms are the sudden temperature rises after long journeys and the history of damage to several engines. Below is a systematic analysis of possible causes and initial steps for further diagnosis:

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### **1. possible causes:**
#### **Cooling circuit:**
- Defective transmission oil cooler:**
- If the transmission oil cooler is leaking or there is a problem with the flow rate, this can lead to overheating. An incorrectly installed or unsuitable spare part cooler could also be the cause.
- The installed cooler with fan could be insufficient or defective.
- Thermostat:**
- A defective thermostat or one that does not open fully could be the cause. It regulates the coolant circuit and may not open the large circuit when temperatures rise.
- Water pump:**
- A defective or inefficient water pump (e.g. due to corrosion or mechanical problems) could impair the coolant flow.
- Radiator fan:**
- The fan could be mechanically or electrically impaired and only fail under increased load.
- Blockage in the cooling system:**
- Residues or deposits could block the flow in the cooling system, which is particularly likely in the case of used spare parts or older parts.

#### **Motor:**
- Damage due to insufficient lubrication:**
- The previous crank bearing damage and piston seizure could have been caused by an inadequate oil supply or quality. The oil circuit of the current engine may also be affected by deposits or defects.
- Defective cylinder head gasket:**
- A leaking cylinder head gasket could lead to mixing of oil and coolant, which can favour both overheating and mechanical damage.

#### **Engine and transmission interaction:**
- Heat transfer from the transmission:**
- An incorrectly functioning transmission oil cooler can transfer heat to the engine and put additional strain on the cooling system.
- Unsuitable or defective spare parts:**
- The replacement engine and the used transmission oil cooler could themselves be the source of the problems, especially if their origin and condition have not been fully checked.

---

### **2. diagnostic suggestions:**
#### **Check the coolant circuit:**
- **Test thermostat and water pump:**
- Check for correct function with cold and warm engine.
- **Cooling system pressure test:**
- Check for leaks or pressure loss, e.g. due to a defective cylinder head gasket.
- Flow test:**
- Ensure that the coolant flows freely through the radiator and the transmission oil cooler.
- Radiator fans and temperature sensors:**
- Test whether the fans are activated correctly at high temperatures.

#### **Check engine and gearbox:**
- Analyse oil quality and condition:**
- Check for metal shavings, water or dirt in the oil.
- Compression test:**
- Ensure that all cylinders are working properly and that there are no leaks.
- **Check transmission oil circuit:**
- Ensure that the transmission oil cooler is correctly installed and that there are no impurities or blockages in the circuit.

#### **Check spare parts:**
- Replacement engine and cooler:**
- Check that the installed parts are actually compatible and in perfect condition.

---

### **3. recommended measures:**
1. optimise coolant circuit:**
- Replace the thermostat and water pump if there is any doubt about their condition.
2. replace transmission oil cooler:**
- If the used radiator does not meet the specifications, an original part should be fitted.
3. flush the cooling system
- A complete cleaning of the system could remove deposits or residues.
4 **Check oil pressure system:**
- Especially after the previous engine damage, it should be ensured that all oil channels are clear.

---
The causes could be a combination of an overloaded or inefficient cooling system and mechanical defects in the engine or transmission. The suggested diagnostic steps should make it possible to narrow down the cause. If no clear cause is found, a more extensive investigation of the entire vehicle history and the replacement engines could be useful.

[Alfan]

A long read, but interesting info!

I may have lost the overview a bit, but when replacing the engine(s) I guess you also had new/other waterpump thermostat and other ancillaries? Same transmission? New/other radiator? If some of this was replaced, I would rule out those being the main cause of the problem.

Were any leaks or water in the oil found in any of the cases?

Can the cooling of the automatic transmission impact the engine directly?

I hope you keep us updated on your progress, also since you have so many years of being behind the wheel of your 164