Thread: What happened to your D3/D4 today?

If your EGR valves still have the coolant bypass valves of earlier 3.0 engines then exhaust gases don't flow through the coolers until the engine is up to temperature so previously very little heat would have been transferred from the exhaust to heat the coolant. However if you've also disabled EGR then there's no hot exhaust gas going into the engine to provide heat which will slow warm-up.

Originally Posted by Graeme

If your EGR valves still have the coolant bypass valves of earlier 3.0 engines then exhaust gases don't flow through the coolers until the engine is up to temperature so previously very little heat would have been transferred from the exhaust to heat the coolant. However if you've also disabled EGR then there's no hot exhaust gas going into the engine to provide heat which will slow warm-up.

EGRs have been disabled and blanked a long time.

The EGR coolers as I understand have no choice but to receive the hot exhaust only they have this coolant travelling around them (shell and tube) to reduce gas temp. That explains why they would provide an immediate boost to coolant warm up speed.

Originally Posted by PerthDisco

EGRs have been disabled and blanked a long time.

The EGR coolers as I understand have no choice but to receive the hot exhaust only they have this coolant travelling around them (shell and tube) to reduce gas temp. That explains why they would provide an immediate boost to coolant warm up speed.

Yep.. And when you follow the flow it also passes the heater matrix also, hence why they warm the heater so quickly. No great loss

The coolers on earlier 3.0s were fitted with a vacuum-operated cooler bypass valve that prevented most of the exhaust gas from travelling through the coolers to ensure that the recirculated exhaust wasn't cooled before going into the air intake. However with the EGR valves blocked, exhaust wouldn't have passed through the coolers even if the cooler bypass valves didn't have the cooler bypassed so shouldn't have been providing much heat.

Your loop hose is allowing cold water from the bottom of the radiator into the warm inlet of the thermostat housing thus changing the percentage of cooled water mixed with hot. Clamping your loop hose should correct the flow through the thermostat housing.

Originally Posted by PerthDisco

The EGRs must be a significant source of heat although the pipe size is small.

There’s no diagram I’ve seen of EU4.

There’s nothing I’ve done by looping it that does replicate the EGR circuit only there’s no EGR heat.

Confusingly the EGR T point crosses between the top radiator hose side and the side of the thermostat the bottom hose goes in so there’s a bob each way as to where it sources supply from.

I’ll also block this circuit off and try that since water flows on the engine side no matter what.

Hope brand new LR thermostat not faulty!

Recent temps on a country run

Those temperatures look more positive however how long and what terrain did you drive through before you received that response. Once you see those temperatures I would be looking for a long downhill run and leaving the car idle for a period to see if the temperatures are sustained. I believe that would indicate if the thermostat is doing its job.

I am looking for some details on the EU4 differences to the EU3 however had no success to date, will advise if I find anything.

So a second drive with plenty of right boot with the bypass loop in place and I could not get the temp above about 57 when stationary.

I then clamped off the bypass loop and after about 10 minutes of similar driving it steadily crept up to 77/79 where it seemed to sit in suburban driving.





I’ll drive like this for a few days but not sure quite how to interpret it. I’m keen to see how it builds from cold start.

Note that the matrix circuit is almost the same as this. A dedicated feed next to top radiator hose that goes through the matrix and back to thermostat along with my bypass loop. The matrix can only heat from the block there’s no EGR interconnection I can see on the EU4.

The water coming out of the top of the engine as I understand is the pressure side whereas the bottom radiator hose is on the suction side of the water pump when thermostat opens.

I removed the top return pipe to the bottle and strong outflow exists at idle.

Originally Posted by Gravy

I am looking for some details on the EU4 differences to the EU3 however had no success to date, will advise if I find anything.

I’m happy the new thermostat and temp sensor appear to be good.

Here’s the best drawings I could find which match my car. My scribbles on them. Several differences to EU3.

Engine (extra pipes are for fuel burning heater option)



Heater Matrix