401 overheating problem.

[jeepman]

i have a scrambler built from scratch,scout dana 44's,4''lift,all fiberglass,ect.have a 401 motor bolted to a 727 tranny.the motor and tranny are both 100% rebuilt.sitting still with 180* thermostat temp. stays at 181-183 for 1/2 hr. or so,but when i get on the highway it will go up to 200-205,maybe higher if i kept going.i've tried other thermostats,3 core rad. is brand new,put shroud on,changed fan,timing,carb.settings,removed bug screen and moved oil cooler to get more air,put on differant aluminum intake,hoses are new.i have a cj5 with a 360 that has cardboard in front of the rad. it runs so cool.any input would be great,thank you

[tufcj]

Fan shroud? Clutched or fixed fan? If the grille is fiberglass, have you added panels forward of the radiator to force air thru, instead of around?

Just some of the things I did to my CJ to solve the overheating problems.

Bob
tufcj

[jeepman]

shroud is on with fixed fan,i tried a clutch fan,no help.with engine idling,it sucks a paper towel against rad. quickly,it is drawing a lot of air.i have a 1-piece tilt frontend on it.i don't have a heater in the jeep yet but that should not affect the over heating issue,i wouldn't think so anyhow.jeepman

[cj5doc]

What kind of RPM are you runnin on the freeway? Is the H20 pump working ok at high rpm?

[jeepman]

i would need to take another ride and look but i believe it is around 2,200 rpms,i have 35'' tires with dana 44's that have the stock 350 gears in them.i may go with a high-flow water pump,not sure if that would help.another thought i had was to change the pulley size on the pump. jeepman

[Brett Polwell]

Are you running a flex fan or the stock fan with a clutch fan eliminator? I think the stock fan on my J20 with a 401 was a 19in 7 blade fan. I locked that up and it would suck a paper towel off the roll hanging on the wall. You can't run the stock fan at high RPM but with a 401 you shouldn't need a lot of rpm.

I would also try the high flow water pump. It helped with my set up. I am running a 401 in a Wrangler. I changed Radiators so I can't run the stock fan anymore without hitting the lower radiator hose. Now I am having heating problems.

Water wetter helps too.

[donwag]

Heavy duty fan clutch, seven blade fan, flowkooler water pump, 180 Robert Shaw high flow thermostat, and a fan shroud.

Two 401's GW and CJ7. Both have stock radiator and above, never any cooling problems. Probably could even use the 190 thermostat and be fine.

[jeepman]

i have a stock fan with a fixed blade[not a clutch fan],i've tried a clutch fan but that was before i rebuilt the motor.this motor had several problems which is why i rebuilt it. someone had 304 heads on it,coolant areas were about 75-85% blocked,ect. motor has been gone through 100% now,and still having over heating issues.my next step is to put a good 7 blade clutch fan on,shroud is on already,i considered the flowkool water pump but i don't know how well they work.i built a serpentine set-up for this motor when i first put it in,when it started running hot on me i went back to the v-belts and had the same problem.thank you guys very much for the help,i'll keep you posted on it. jeepman

[dooghssr]

I had the same issue w/my 401. Actually a thread on here. Tried the timing, radiator, carb, etc, etc. Put on a Ford Taurus 3.0 fan from the junk yard. Paid 25 bucks. Thing runs almost too cool now.

[jeepman]

what year?i guess your'e talking electric fan.i'll give that some thought,i tried a electric fan but that was before i rebuilt the motor.john

[82Waggy]

Are you running vacuum advance?

[jeepman]

yes, i have an hei dist. in it. john

[82Waggy]

What oil are you running? Not 20w50 or some such nonsense I hope.

[jeepman]

10w30 oil.

[82Waggy]

Well, not sure what may be going on here. Many internal things can cause overheating, like bad head gasket seal, detonation, poor lubrication, low oil level, high oil level, valve issues, tight pistons/rings, cracked head, etc.

Other possibilities include, bad water pump, slipping belts, sticking thermostat, blocked radiator passages.

You may not be able to solve the problem until you do a tear down inspection of the internals.

Assume you have checked for the obvious such as loss/using of coolant, plugs that indicate water injestion or excessive carbon, lean burn, cranking pressure at all cylinders...

[Blown7]

Well on the highway the fan is not needed anyway IF you have good enough airflow..........
So what is stopping the airflow? Or waterflow?

[jeepman]

i just went for a test ride after putting on a 17''clutch fan,kool-flow water pump and a robert shaw 180*thermostat.it runs much cooler now,i need to take it on a longer run for the real test.i'll keep you posted on what happens, jeepman

[jeepman]

well,hauled my car trailor with a 95 yj on it to drop it off about 15 miles away,mostly highway with a few stop lights.each time i stopped at a light the temp. went up a little.when i got to where i was going it was 205-210.let it idle while i unloaded the yj.it was back down to 185 or so with-in a few minutes.i'm about one step from pulling this 401 out and putting in a 360 i have sitting in the shop.i don't understand what could be differant in a 401 block vs. a 360 in my cj5 that i can't get to heat up,i have cardboard in front of the rad. all winter.i don't have a heater in it,it would help a little but that shouldn't be causing this problem. john

[65postgs]

My CJ5 with 401 has a stock 304 radiator, clutch fan, flowkooler high flow pump and high flow thermostat(195). No issues even in the 90 degree summer days.

[413 Wrangler]

Hope this helps.

*401 + 0.060" (not the best idea)
*Jeep Wrangler = small radiator but 2 core w/ 1" tubes
*Novak or Be Cool aluminum (both worked same for me)
*Spal 16" fan, set to come on at 170 F (+ a manual over-ride)
*No mechanical fan
*Flow Kooler WP
*Shaw 160 F by-pass thermostat
*Bulltear 8 qt. oil pan (also helped cool the motor slightly)

Live at 4100' elevation w/ 95 F ambient temps. in Summer and can keep in below 180 F if I want.

[jeepman]

well,i've discovered another piece to this riddle.after towing last week and it started running warm again,i got home and pulled it in the shop,never touched it until sat.i raised the hood and the top rad. hose was collapsed.replaced the hose and got to thinking,the overflow tank is s.s. round canister with no vent and the hose just goes onto a fitting on the top,it doesn't go down into the canister.may or may not be a problem,not sure at this point.

[Mudrat]

Could very well be a part of your over-heating issue!
You need to vent the radiator over flow and ensure the pick-up hose is near the bottom - otherwise what good is it doing?

Remember the heat/cooling cycle of the whole 'system' :
As the coolant heats up it will naturally expand and flow past the *16LB* (some are 17 or 18LB) rad cap and should flow easily into the overflow tank (the need for the tank vent).
After you stop and the coolant cools and contracts, it needs easily to suck the coolant back out of the (vented) tank (the reason for the collapsed hose?).
The radiator cap is what keeps the cooling system 'pressurized' to raise the boiling point of the fluid. It is not a sealed system, but a closed system. The rate of flow into or out of the tank is not fast so a small hole is all that's needed in the top or the cover.
A 1/4" would be plenty, and you can put a nipple on it or a filter if you're headed through the mud or nasty water routinely.

[82Waggy]

well,i've discovered another piece to this riddle.after towing last week and it started running warm again,i got home and pulled it in the shop,never touched it until sat.i raised the hood and the top rad. hose was collapsed.replaced the hose and got to thinking,the overflow tank is s.s. round canister with no vent and the hose just goes onto a fitting on the top,it doesn't go down into the canister.may or may not be a problem,not sure at this point.

System can't purge air if it has no way for the coolant to expand (no vent in the overflow canister). If overflow bottle was vented, it would only pull air back into the system since it cant pick up the expanded coolant from the bottom of the bottle as the system cools.

[jeepman]

i now have a new top rad. hose on motor,new factory style overflow coolant bottle and new hose running to it.now i'm waiting on a warmer day,with no heater in jeep yet it is a little cool to ride in.i'll keep you updated,thanks again. john

[jeepnmatt]

what intake manifold are you running?

[jeepman]

i had a edlbrock.i wanted to try another intake so i had a offenhauser on the shelf that i put on.had the same results.the only change was the edlebrock seemed to idle just a little better.still have not taken jeep for a ride,we have had some snow storms that got in the way. thanks, john