Basics-
96 F350 Duallie box truck
2wd
5 speed manual
460
147k

Background-
Truck is used by the county schools maintenance... mostly around town stop and go b/w the various schools and the shop... very little high speed driving in its life. The damn thing overheats... anytime the a/c is on or if it is taken on the interstate. Runs warmer than it should the rest of the time now that its gotten warmer. According to the driver (whos had this truck since it was new) its been doing this for the past 5 years throughout the warm months... otherwise runs perfectly
the shop i work for got this contract a couple years back.. and we haven't actually worked on this issue before, so all i have to go on is what looks new and what he says

Replaced so far-
Thermostat (multiple times)
Fan clutch (multiple times)
Radiator
Rad. cap
Water Pump
All hoses
2 freeze plugs that were leaking- i did this and rinsed the block out as well as i could while i had 'em out

Verified accuracy of gauge

it slowly crawls across the normal range while driving... even when babying it... run it hard and it progresses alot faster... will not cool back down unless shut off

I'm getting suspicious of the oil cooler being plugged up... this has the full flow type that is crammed in the middle of the lower rad. hose... anyone had/heard of these being problematic for clogging and restricting coolant flow?

Any other ideas?
This thing is giving me nightmares

3/23/2007 8:31:39 PM

You got plugged up head coolant passages. Probably scale buildup across head gasket holes.

I'll bet ten cheeseburgers, a large pizza pie, and a case of beer on it.

3/23/2007 9:15:56 PM

ill bet the fucking condensor fins are smashed all to shit causing a loss of airflow to the radiator. he did say it overheats any time the a/c is on.

3/23/2007 9:48:12 PM

^ Condenser fins are in pretty dang good shape- forgot to mention that

^^ now thats the kinda thing i'm hoping its not... i may be pullin the heads monday

3/23/2007 10:20:12 PM

plugged up coolant passages and or leaking head gasket

3/23/2007 10:46:06 PM

^yep. both somewhat common issues on higher mileage 460's.

i assume you've made sure there are no air pockets in the system?

3/23/2007 10:55:52 PM

^ No air in system for sure.. i've pulled every hose and sensor loose just to make sure there wasnt a bubble stuck in there

^^ Head gasket isnt leaking... no longer losing coolant since i replaced the freeze plugs- no combustion gases in the coolant according to the test strips either.... Looks like i'll be tearin 'er down

3/24/2007 12:19:20 PM

make sure the overflow is working correctly also. guy i know had a 460 in an f250 that was sucking air back into the system that way.

3/24/2007 12:56:55 PM