Misc Radiator Cap Leak and Cooling System Refresh

[jdemong]

Hi all,

I've had a 1980 CJ for nearly 9 years now. It was built with a Chevy 350 swap by a previous owner. By the time I got it, it no longer ran, so starting in 2022 I went through the process of getting it running, replacing the fuel system, refreshing the suspension, and tidying up wiring to get it inspected and registered.

Last summer I finally decided to attack the cooling system. It looks I have the radiator from a 2.5L/4 cyl CJ to suit the inlet and outlet of the 350. I pulled out the 165F thermostat and ran kleen-flo rad flush through the system and then flushed with water probably 6 or 7 times as well as running water directly through the rad and the block to try to clean everything out. The flush water still looked a little hazy, but it was clean enough for me and I wanted to drive the thing. I replaced the thermostat with a 180F thermostat (I live in Canada, Jeep came from AZ), put a new o-ring in the water neck (Mr. Gasket style sbc water neck), installed an amazon stainless overflow reservoir, filled with fresh coolant, replaced the rad cap, and ensured the e-fan kicked on.

After all that here's what I've noticed:

1. Rather than filling my overflow bottle nicely, coolant tends to leak out of the radiator around the cap from what I can tell. The cap is new and the hose doesn't seem like it's restricted, but I'm planning to replace it with some new silicone hose to be safe. It also doesn't appear that the radiator sucks coolant back into it as it cools, and I don't know if I need a different rad cap to allow for this.
2. I keep getting water leaks from the water neck. Looks like I'm melting water neck o-rings. I decided to try the Mr. Gasket branded o-rings as these are supposed to be silicone and that means good temp resistance, but haven't gotten a lot of run time on it yet so I don't know how it's holding up.
3. I find that the temp gauge on the dash doesn't move very high at normal operating temp, creeping just over the lower end of the gauge, even after replacing the sender.

With all that in mind, does anyone have any suggestions of things to try or look at as I try to get the jeep going again for this summer? Thanks in advance!

TL;DR: My rad cap is leaking and I'm melting or damaging water neck o-rings. What do I need to look at?

Cheers,
jd

 

[jdemong]

The Jeep in question:

 

[TSB8C]

It certainly seems your water temp is exceeding what your gauge is reading. To reach a temp where coolant is exiting the radiator and going to the overflow bottle, as well as melting o-rings, that temp has to be higher than the gauge reading of "just over the lower end of the gauge" as you stated. So need to get that resolved. You said you replaced the temp sending unit, so time to look at the gauge itself for why the wrong reading.

Your radiator seems too small to me. I also have a SBC350 with a 190 degree thermostat (running EFI). That radiator designed for the 2.5L/4 cyl engine probably can't handle that SBC. I suggest a 3 or 4 core aluminum radiator made for this setup. Since SBC swaps are so common in CJs, you can buy radiators made for the SBC with the correct size and mounts to fit the CJ grill. Mine even has the extra part for an auto Transmission as well. I suspect your temp is getting hotter than your gauge is telling you. In terms of an e-fan, my SBC couldn't stay cooled enough with a single centered fan. I added vents in the shroud for better air flow, a dual fan and dual speed setup from a Ford Contour, and vents in the sides of the hood to solve my temp problem.

If the radiator cap is leaking, then you have an issue with the overflow system, and/or the radiator neck where the cap is screwed on. Excess pressure or expansion of coolant should exit the nipple and go to the bottle. If it's leaking around the cap itself, and you already replaced the cap, the rubber seal on the underside the cap is not sealing inside the base of the neck, or the cap is the wrong size, or perhaps there's a small hairline crack in the radiator neck.

I've never been a fan of the water neck o-rings. I prefer the gaskets. Heard/seen too many reports of the o-rings getting warped when the water neck bolts are over tightened, getting dried and cracked (depending on coolant mix ratio and type), etc. But in terms of "melting" an o-ring, that would take a lot of heat. So is it really warping out of shape or is your coolant really getting that hot?

Great looking CJ by the way.

 

[jdemong]

Thank you, and thanks for the thoughtful reply. I suppose a good place to start to get another temp gauge on it that gives me a proper temperature feedback and go from there. What do you tend to shoot for for a normal operating temperature on your Jeep?

I've been eyeing an aluminum 3 core on eBay for the past year, so I'll go ahead with that if I am overheating with the new gauge. I'll also take a closer look at the radiator neck.

I'll try to get a picture of the latest seal, it should still be in the trash bin, but it really looks like it's melted, not warped. If the upper limit of a typical o-ring is 250 then that confirms that I might have been actually overheating all this time, I just didn't expect that because of the gauge.

If I have naively been overheating this engine repeatedly, is there anything else you'd recommend looking at such as head gaskets?

Cheers,

 

[TSB8C]

Mine runs around 180-190 most of the time. A hot summer day on the interstate at 75 mph may see 195-200; hence the air vents and hood scoop. Was seeing higher than that some times on extended high speed trips before the added ventilation and the pass-thru vents in the radiator shroud. Now remember that EFI is designed to run warmer than most carb setups. So 190 is the thermostat my Crate engine came with and is designed to run at. A carbureted SBC, depending on some other factors, would usually have a 165-180 thermostat in it. Nevertheless, 180 is a good target temp to stay around for most carbureted applications.

If you discover you've been overheating on a repeat basis, especially enough to melt water neck o-rings, definitely head gaskets and valve seals should be evaluated. Ever any knocking/pinging from early detonation? That's another sign of overheating.

 

[flyn hawaiian]

Hi all,

I've had a 1980 CJ for nearly 9 years now. It was built with a Chevy 350 swap by a previous owner. By the time I got it, it no longer ran, so starting in 2022 I went through the process of getting it running, replacing the fuel system, refreshing the suspension, and tidying up wiring to get it inspected and registered.

Last summer I finally decided to attack the cooling system. It looks I have the radiator from a 2.5L/4 cyl CJ to suit the inlet and outlet of the 350. I pulled out the 165F thermostat and ran kleen-flo rad flush through the system and then flushed with water probably 6 or 7 times as well as running water directly through the rad and the block to try to clean everything out. The flush water still looked a little hazy, but it was clean enough for me and I wanted to drive the thing. I replaced the thermostat with a 180F thermostat (I live in Canada, Jeep came from AZ), put a new o-ring in the water neck (Mr. Gasket style sbc water neck), installed an amazon stainless overflow reservoir, filled with fresh coolant, replaced the rad cap, and ensured the e-fan kicked on.

After all that here's what I've noticed:

1. Rather than filling my overflow bottle nicely, coolant tends to leak out of the radiator around the cap from what I can tell. The cap is new and the hose doesn't seem like it's restricted, but I'm planning to replace it with some new silicone hose to be safe. It also doesn't appear that the radiator sucks coolant back into it as it cools, and I don't know if I need a different rad cap to allow for this.
2. I keep getting water leaks from the water neck. Looks like I'm melting water neck o-rings. I decided to try the Mr. Gasket branded o-rings as these are supposed to be silicone and that means good temp resistance, but haven't gotten a lot of run time on it yet so I don't know how it's holding up.
3. I find that the temp gauge on the dash doesn't move very high at normal operating temp, creeping just over the lower end of the gauge, even after replacing the sender.

With all that in mind, does anyone have any suggestions of things to try or look at as I try to get the jeep going again for this summer? Thanks in advance!

TL;DR: My rad cap is leaking and I'm melting or damaging water neck o-rings. What do I need to look at?

Cheers,
jd

I have a 383 stroker in 78 CJ5 . I don't use o ring on the thermostat housing. I use a gasket. I also use a radiator cap with the purge lever ( don't think it matters). I also have a 4 core aluminum radiator with elec.fan. Temp is 185 degrees.If your cap is leaking, Iwould change it