ok, i'm lookiing for suggestoin i may have over looked... in az hot here. 78 bronco351m all std inside but has been ovehauked in past. was running warm , has new sever duty fan clutch, new peak /distilled watrer mix. new flow cooler waterpump, a new robert shaw 180 thermostat, timing @10-12 degrees. runs great. new 3 core fully tig welded alum. radiator, ( expensive style) thermo vaccum swith new AND properly hooked up, new can have tried 13lbs and 16 lbs. all hoses new. and yes shroud is there. fan on correct way. all is good for 1st starting out, and low speeds, but after being on freeway for @ 5 -10 miles, temp climbs up my aftermarket temp gauge reads 200-220 and then cooles down, was reading 230 with the 195 t- stat. and yes was the motorceaft rt 139 351m/400m as needed.. new stat just robert shaw style. whe i pull in driveway can hear the fan running and is pulling air, quite a bit when engauged. but seam to reve it up to get it going, did the same with the old fan clutch, std a/c model. gooing to a diresct drive fan for now, it does cool down when idling,.. is there something i am over looking????? really stratching my head here... thanks...

 

I would double check your temp readings . I have seen many aftermarket gauges be off by 10 to 30 degrees ! An IR temp gun would be a good tool now . You can ck actual temps and ck for flow and temp drop at the proper places .

 

Do you have a spring in your lower radiator hose? Without the spring, the lower hose can supposedly collapse at higher RPM and limit coolant flow.

 

your right about the hose and spring, the original had one fell appart in my hands, and replaement didn't come with one.i don't believe this is the case but i will look into it. but was running hot before i did all this work to it.as for the temp gun i agree just keep forgettting to bring it home from work to see.... muy factroy auge reads in the upper range, and a/c aint even on... and when this is the gague is reading @200-210 but hs 180 stat? now the aftermarket tempo probe is in the themostat neck, only place i saw to plum into with out major mods.... has anyone out there experiacned a hot running351m? been a dodge gut ofr years, and have had some 360-390 and 302 rollers. but never a 351/400m.... new stuff for me...

 

Double check and make sure you have the right thermostat installed Check this thread https://www.ford-trucks.com/forums/1...errerid=613652

 

Overheating while on the highway usually indicates poor coolant flow, so I would try a new spring, just to rule that out. You should be able to find something to work at a good hardware store with a selection of springs.

 

any issues with blocked coolant passenges i heads or block knwn to be problems? was sitting for a while.... and as for the propper t- stat it did have the rt-139 ran hot, repalced with t a robert shaw 180 designed for the 351m with the block off passage to center in housing.. just tring not to tear into an engine that doesn't ned it. like i said runs awsome ...

 

Agree hot on a roll/cool at idle usually means inadequate coolant flow or inadequate radiator. The fan does not do much when moving faster than 30-40 MPH. Ram air takes over. Suggest you leave the fan part alone for now and look after coolant flow. It sounds like you have a good radiator so that's out

Spring in lower hose, factory replacement water neck and factory replacement T stat as mentioned above would be my suggestion. The factory stat (192 deg I believe) should be fully open by 200 or so so the stat temp rating is not your problem.

I am not familiar with the "flow cooler" water pump. In general, capability of aftermarket pumps varies. Perhaps somebody has experience.

I know my '78 400 does fine in the 95-100 degree weather we get here. It has all stock replacement stuff: new NAPA replacement water pump, OE stat housing, Autozone factory replacement stat, Autozone 3 core radiator (higher capacity OE style), stock style thermal clutch fan to replace original fixed. With extended idling in hot weather it will warm up a bit but not overheat. On a roll, it cools right down to stat temperature.

 

If you can't find a coil for the rad hose then they're easy to make. I used 14 gauge galvanized wire that I wound around a 2" dowel.
Heating up on the highway can also be caused by lack of airflow thru the rad. You need to create a low pressure area behind and below the rad to get the high pressure air to flow thru the rad. An air dam installed directly under the rad will do this. The dam only needs to be 3-4" high. I've adapted some air dams from other cars/trucks and have built them out of plexi-glass too.

 

sounds like it might be running lean at higher rpms heating up that fast what size carb are you running? is it duraspark or hei have you tried pulling back the timing a hair the curve might be off advancing too much when revved. Is the timing chain new or well used if its stretched timing can be all over the place.or it could be a ten buck thermostat good luck.

 

well timing chain is new, and all original motor, even the carb. like i said runs great, being off today, i yaked it appart to recheck eerything, i did find that the robert shaw t-stat from summit is a 332-180, not a 333-180, they lokk near identical, possibly it. i researched and found a 332 to fit the old caddy 500+ big blocks... this i think is my problem. but compared to pics on this web page, they look identical, but has a 332 stamped on it. orignialy new custom radiator cam e with a new cap. but didn't work and would not hold pressure pas 10lbs rated 16lbs. i reassembled with this 3232 t- stat not knowing, and a new stant 16lb cap. and was dealing with the overheat after a while running. will retrend after i reassemble with the new parts on order to let you all know.. thanks

 

new topic, also have rebuit the front end with poly. i mean everything, and put a 2 degree cater c bushing in it, new skyjacker hydro 7000 shocks, all 4 and new dual steering stabilizers. all joints good, good ball joints, new wheel bearings and tires, and balanced , aligned in specs. still has a a loose wandering feel going straight. like fighting is and very loose, orignal steering gear. and the worm gear wont turn t i tighten up, possibly the box and rag joint? either don't see any play but ae old. anyone experianced it?

 

Sounds like the 332 is your problem. Napa carries the correct 'stat...