Hi,

I recently bought a 1989 E350 460 7.5. Have done some work on it already and thought I have fixed the major issue but now I’m getting an overheating issue. Coolant level is good and fan is working. Can anyone guide me on what I should do next to diagnosing it?

 

Temporarily remove any installed thermostat and test again. Double check the water pump impeller is circulating coolant. Check radiator for clogs or other major restrictions.

How have you so far determined it is indeed "overheating"?

 

Overheating under what conditions? High-speed highway driving or sitting for long periods in traffic?

What was the 'major issue' that needed to be fixed?

Look around on this site. It has some good basic info on what to look for. The Haynes and other manuals also have basic troubleshooting sections:

https://www.aa1car.com/library/overheat.htm

 

I'm gonna share what I learned with an overheating issue.

Driving around on flat ground in temps up to 95 degrees all was good.
Now, if the outside temperature was in the 100's, and climbing up long grades into the mountains, the engine would overheat.
By "overheat" i'm talking Coolant Belch out the overflow like a jet-stream or Steam-Engine.

I took the rig to my local radiator shop (in Shasta County, Ca., it is Rod's Radiator, and owner Mike).
With the engine running, he carefully checked coolant temps at thermostat housing, hoses and radiator.
Mike's conclusion: "I think your overheating issue is not your radiator, and is elsewhere."

I go home and thoroughly clean the engine to repaint it after the Coolant Belching incident.
Oh, yeah, the Coolant belching and overheating was day one of a scheduled three-day outing 200-miles from home.
I had my oldest daughter, age 36 with me and we had Casino hotel reservations for 3-nights, so the engine was going to be giving me fits for 3-days before going back to the barn. ( I had lots of water to feed the "Belcher". hahaha

Back to the engine cleaning:
So, as I am looking at the clean engine analising what accessories to remove first, I had a Spotting, being a Broken head bolt.
No kidding, the head of a lower head bolt was MISSING. Hmm, that right there explains "your overheating issue is elsewhere."

I shared my misery with a friend, and he prompltly said "weld a nut to the end of the broken bolt, and try to remove it."
After twisting off two nuts, I decided the Third-time-is-the-Charm. This entailed removing the right side exh manifold for better access for mig-welding the Third nut with both hands, and not single handed messy-mess. Uh-huh.
Two afternoon's later off came the exh manifold and laying on it was the HEAD to the broken bolt.
I phoned a jeep wrecking yard in Antelope, Ca, (J & W Auto Wrecking) and had him send me two original head bolts, one for backup, and installed the replacement head bolt for the clamping for that cylinder. Boom, overheating issue solved.

Once the engine reached an operating temp of 220, the temp, the head would loose it's clamping and combustion would pressurize the cooling system causing the BELCHING. Sometimes the culprit may be a crack in a head or block that opens.

This might help someone diagnose a Coolant Belching issue.
A non-functional Fan Clutch will make an engine overheat and belch coolant too.

What I am leading up to here, also is that a "stretched" head bolt and cause coolant belching same as the broken bolt.