ok i am writing this so anyone who has concidered a diesel with an overheating problem knows what to check first. The 1984 ford f350 diesel with 420 ci (6.9L) international v8 engine that i bought "just needs a thermostat" as i was told repeatedly.
So i had no fear and bought it after looking for water in the oil (no creamy!). The days went buy and i drove it here and there with little to no overheating so i thought maybe air bubbles. Then it happened boom! hiss! and gauge was fully hot. luckily the heater core busted and relieved the pressure. Ah stopped heater core i said....wrong. I drove it home after cooling and watched the gauge creep hotter. So being the smart guy i bought a manual that said it covered the 6.9l diesel but it left out one little detail where is the thermostat and how do i change it. So i checked the internet and found a post that warned about using thermostats that are aftermarket but told me the thermostat was on the driver side which is wrong. The thermostat is on the passenger side or top water outlet. you must disconnect both ground terminals, remove the alternator...smog pump...,and all related brackets. make sure you clean all gasket material from both the outlet and engine surface. make sure you have a diesel thermostat ford part number E5TZ - 8575 - C. it has a special bypass that a gasoline style thermostat lacks. I removed the driver side inlet and found out the info on the web was wrong a 35193 outlet gasket from autozone and a thin coat of high tack (the only gasket adheasive you will ever need) and it was back together. After taking the steps i wrote above on the passenger side i found an ordinary thermostat which had i not bought an oem thermostat would have looked fine and checked out good leaving me with the same problem. you have to verify that what you remove is what belongs especially when it is a thermostat for a diesel ford. i have pictures of the two thermostats but do not know how to post them here if one can post pics.
the 1984 F350 had 73,000 actual miles and looking at the gasket i removed most of those miles spent on a farm were with the wrong thermostat installed. Luckily in my case the head was not damaged. The wrong thermostat in a diesel engine can crack or warp a head and ruin a great diesel engine. in my case it only cost me a heater core and the hoses i cut and spliced to get me home. "yes you can bypass the heater core in a pinch if enough hose is available" Good luck with your diesel and i hope this helps.
Gas Thermostats can cause real trouble
thanks for the replies
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