Engine/Transmission (1998.5 - 2002) Fuel Cooler

[jrandol]

Planning my LP relocation right now and wondering if I should do a Fuel cooler system prior to reaching the Stock Fuel Filter. I know that after running for several miles in even 80 degree ambient tempatures it doesnt take long to warmup up the fuel well past 100 degrees after the return line starts sending warm fuel back to the tank. Summit racing sells fuel coolers for $35 or I am sure I could find a oil cooler setup to use and mount under the truck to cool the fuel some prior to entry in the injection pump. What do you guys think, is this a worthy investment?

 

[TomGolden]

Honestly, yes, I would love to do this also. I posted a similar question about a year ago, and most replies were favorable to doing this. However, most people seemed to think it would be better to put the cooler in the fuel return line, so the fuel is cooled upon returning to the tank. I thought that sounded very odd, because I would expect that it is better to have cooler fuel going into the VP44 than back into the tank.



So, when I get around to doing my own fuel system, I am going to very seriously consider adding a cooler. I have also looked at the Summit coolers you mentioned, and think they would be great for this.



Tom

 

[TxDieselKid]

HERE is a good thread on this topic. The best thread I can remember on it at least. Hope it helps.



Andrew

 

[illflem]

Maybe not in Calif but for sure in Colorado I'd think you'd want provisions for bypassing the cooler when the temp dips too cold.

When it starts getting complicated it makes me wonder if it's worth it.

 

[TomGolden]

Bill, I had thought about adding that very thought to my post above... That in the winter, it would likely be a good idea to remove the cooler from the fuel lines. I go hunting every October/November time frame in places like Colorado, Wyoming, Utah, etc. , and temps as you know so well get quite cold.



Tom

 

[JJW_ND]

Does a 24V return as much and as warm?

Does the 24V pump return as much and as warm a fuel as the 12V motors?



Thank god the 12V does for us up here in cold county.



Simple fuel systems mean reliablity. Wonder if just more fuel capacity or keeping the stock tank full is good enough.



Has there been warm fuel problems?



jjw

ND

 

[TowPro]

According to what I read in the VW forum, Hot diesel works better then cold diesel fuel. I think I have read where one of the controls on the TDI is fuel temp. They use that measurement when deciding how much timing to use on the Injection cycle.



guys have been faking out the computer, telling it the fuel temp is higher then it really is for a performance gain.



Not sure if our trucks have an ECM input for fuel temp, if it does you may be shooting yourself in the foot.



Now with Gas engines I think I understand they want to cool the fuel to make it less volatile, lower volatile fuel has a slower burn rate, which would be like a higher octane.

 

[RustyJC]

Originally posted by TowPro

According to what I read in the VW forum, hot diesel works better then cold diesel fuel.

Bingo!



From a purely thermodynamic point of view, insofar as a diesel engine is concerned, the hotter the fuel when it's injected into the cylinder, the better (remember, we're dealing with a heat engine. ) Hotter fuel would also have some flow advantages due to lower viscosity. We've done all the work of compression to get the air in the chamber hot enough to ignite the injected fuel, and the final heat of combustion is going to be a great determinant in the amount of power we can produce and extract (the higher the temperature, the higher the cylinder pressure. ) Why do I want to inject cold fuel and drag combustion temperatures down?



Having said that, cooler fuel might be of benefit in terms of cooling the VP-44. Otherwise, why do I want to cool it?



Rusty

 

[RustyJC]

Originally posted by TowPro

Guys have been faking out the computer, telling it the fuel temp is higher then it really is for a performance gain.

Since the density of the diesel fuel will decrease with temperature, apparently the VW ECM tells the injection pump (a VP-44, right?) to compensate by lengthening injection duration as fuel temperature increases. Therefore, telling the computer that fuel temperature is higher than it really is would result in slightly longer injection duration - more fuel than "normal", and thus more power.



Rusty

 

[illflem]

Another plus- I read an article that showed better injector pattern and atomization with higher fuel temps. Some big rigs have fuel temp gauges but they use them on the low end to signal when it's time to turn on the tank heaters, don't do anything on the high end.

 

[David Oxland]

Mostly a cooler would be counterproductive. Many industrial engines burning ordinary fuel have jacket water heater exchangers to get the fuel temp up to jacket water temp. Hot fuel atomizes better, therefore starts combustion promptly therefore quieter and more fuel efficient. Most of the engines I work around are taking fuel into the fuel pump at 90C or about 190F.

David

 

[Turbo Horseman]

I'm with JJW-ND, better to have warm fuel in the cold temps and kiss the fuel system.



Just one thing... JJW-ND, it starts to get cold at 6 - 8 weeks of minus 30 or less:--) at a time.