Diesel leaking into Coolant?

[DieselScout]

Is it possible for Diesel fuel to leak into the Cooling system in the D24 NA engine?

I added dye to my fuel to trace a leak on my injection pump,
While shining the UV light, I noticed a leak on the block coolant sensor, which I apparently did not fully tighten the other week

I am using a green coolant, but it seemed more fluorescent under the UV than it should’ve been.

Also of note….my wagon does suffer poorer fuel economy and higher engine temperatures (compared to my other 2 diesels)

After some quick research, it would appear that the issue with other diesel engines could be with the “Injector Sleeves/Cups?”
Does the D24 have these?

[ngoma]

Not really. More likely is that your (dyed) fuel has externally dripped down onto the sensor. Remember, diesel fuel is an oil-- if it was present in the coolant you should see a oil sheen on the surface in the coolant overflow bottle. But there is no easy way for fuel to get into the coolant.

Another thought: Have you experimented shining the light on virgin coolant straight from the jug? Does it glow similarly to what you saw at the sensor?

As far as the temperature differences: How are you measuring? If you are going by the instrument panel temp. gauge that is not a reliable measure of true temperature.

Fuel economy differences could have numerous reasons.

Cups/sleeves? Please explain better.

[v8volvo]

Good news is the injector cups or sleeves you're reading about don't exist on a D24 type engine. On a D24 the injectors screw into the head from the outside, with external supply and return plumbing and no internal fuel system plumbing, so any fuel leaks that may occur will leak fuel outside the engine rather than inside it.

Many engines with "unit injector" or HEUI or common rail injection systems instead use internal fuel galleries in the cylinder head for injector fuel supply and/or return. On some of those designs, the injector bore and fuel galleries are separated from the coolant passages by a brass cup or sleeve that is pressed into the head. If that cup cracks or loosens up, it allows pressurized fuel to leak into the cooling system and contaminate the coolant. 7.3L Powerstroke engines are the best known offenders with this issue. That may be the concern you have read about but luckily it is an issue your engine is not vulnerable to.

See ngoma's notes about tracing fuel leaks. Another note -- fuel oil spreads easily and far when it is even a small leak, and airflow from the radiator fan can blow it backwards and even upwards making it hard to find the original source. Seeping rubber injector return lines are a prevalent culprit though.

[DieselScout]

RE: Fuel in Coolant
That's good to know.

Perhaps I unknowingly got some fuel on the sensor when I was working on it last week...

I did find the fuel leak I was initially looking for; it's on the engine-side of the injection pump.

RE: Higher temperatures.
I installed water temp senders in the coolant return hose (to the radiator) and my wagon reads an average of 10F-20F higher than my sedan. It also gets up to temperature much faster.

I installed an 80C thermostat in my Wagon the other week after suspecting (haven't yet confirmed) that my sedan has an 80C thermostat. The wagon is now averaging 190-190F versus the sedan with is around 175-180F.

I have not yet had the chance to test steep hills, but in the past, my wagon temperature would spike/increase during sustained highway travel and up hills, causing several hoses to burst.

[ngoma]

Originally Posted by DieselScout

I installed an 80C thermostat in my Wagon the other week after suspecting (haven't yet confirmed) that my sedan has an 80C thermostat. The wagon is now averaging 190-190F versus the sedan with is around 175-180F.

To get to the bottom of this you will need to benchtest each tstat by heating them/cooling them in a pot of water on the stove with a thermometer. Not uncommon for them to vary quite a bit from their ratings.

Originally Posted by DieselScout

I have not yet had the chance to test steep hills, but in the past, my wagon temperature would spike/increase during sustained highway travel and up hills, causing several hoses to burst.

Things to look at:
Radiator condition
Thermostat functionality (sticking? sluggish?)
Water pump condition, style, design (some are more efficient than others)

Burst hoses:
Expansion tank cap rating. Recommend use the black (lower pressure)
Hose condition, age. Did they ever get oil or fuel soaked?