Engine overheating when driving/idling - What to check?

[Jonas_R]

So my newly build engine is messing with me... Arg

No overheating issue before rebuild.

Engine has been completely rebuild.
New Thermostat
New water pump
Old main rad
New hoses
old afterrun pump

Symptoms are:

When running straight ahead doing maybe 50 km/h and heating set to max temp on the G62 will climb to 95-97°C.
When idling it will be around 93°C with heater set to max.

If I don't set heater to max temp will rise.

What have I done so far:

Now I have bleed the system and only fluid comes out at heater matrix and main rad.

When I touch the bottom hose from the main rad it is very cold and top hose is very hot.

I believe next step would to pull bottom hose and see if fluid comes out of the main rad?

If indeed it does the I guess my thermostat is stuck closed?

I'm missing anything else?

[morgenlatte]

dumb question, but is the thermostate built in correctly?
do you have an auxillary radiator?

[RichLV]

Bottom hoses are being opened up by thermostats if I recall correctly. Maybe you got dealt a bad one?

[Jonas_R]

dumb question, but is the thermostate built in correctly?
do you have an auxillary radiator?

Yeah it should be but that could be it of course.

[Jonas_R]

Bottom hoses are being opened up by thermostats if I recall correctly. Maybe you got dealt a bad one?

According to Dave/urs4boy flow diagram then flow goes into top of the rad and out in the bottom.

So yes the thermostat could be bad. If it stay closed then I guess the bottom hose would be cold?

But the bottom hose is hot at the entry to the thermostat but cold at the bottom of the rad.

[morgenlatte]

thermostate should be in this way:

the reason i asked for a auxillary radiator is, because if it is a bad one, the hot water gets bypassed over the main radiator and therefore it overheats

[RichLV]

My presumption would be that it does not open the extended loop when car get's to the needed temperature, hence it is flowing only through the small loop. At least that's my previous experience with overheats & bad thermostats. Bottom rad hoses were always cold in these cases.

[Jonas_R]

thermostate should be in this way:

the reason i asked for a auxillary radiator is, because if it is a bad one, the hot water gets bypassed over the main radiator and therefore it overheats

Aux rad is new and was working before engine rebuild. But bad in what way? If it is blocked then why would it effect the main rad?

[Jonas_R]

My presumption would be that it does not open the extended loop when car get's to the needed temperature, hence it is flowing only through the small loop. At least that's my previous experience with overheats & bad thermostats. Bottom rad hoses were always cold in these cases.

I agree if there is flow through the main rad, if main rad is blocked that would give the same symptoms.

[SteveH]

The last thermostat I installed gave the same problem. Faulty thermostat or incorrectly fitted.

[Jonas_R]

The last thermostat I installed gave the same problem. Faulty thermostat or incorrectly fitted.

Alright.

Can you change the thermostat without removing the main rad?

[Drummer87]

I mind a dodgy stat from Audi wouldn't open. Tested in Boulder water when removed to confirm.

[Jonas_R]

Good point, always good to know the root cause of the problem.

[SteveH]

Alright.

Can you change the thermostat without removing the main rad?

Yes, it's just two M5 bolts from memory. I used allen heads, as they are easier to get to from different angles.

[Drummer87]

Remove the housing and gain access simples compared to other engines

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