Coolant wtff?

[Jppr26]

So I’ve replaced everything but the hoses on my 87 v20 sb350 cooling System hopefully this was the last issue.

Recently replaced the radiator because mine was missing a lot of fins, my new radiator was the HD above stock other than that, nothing special, let it run and get hot added water as the thermostat opened and made sure it was topped off good. I took it for a drive the other day and was about 4 miles from the house and the radiator cap blew off, I figured I didn’t get it tight enough, rilled it back up with water and reinstalled the cap tightly on and about 15-20 miles down the road it did it again, I added more water and reinstalled the cap again, and made it to my brothers house another 3 miles down the road.

We were thinking it’s something simple like maybe I should have got a new cap with my radiator instead of using my old one, I have no signs of a bad head gasket, so he gave me the radiator cap off his 67, and I drove home with no problems, got me a new cap the other day and no problems yet

 

[da_raabi]

Since it was old the cap might have stuck shut instead of venting excess pressure. If the new cap fixed it I bet that was it.

 

[Obwonkonobe]

Yup, get a 16 pound cap if this one blows, that's what works for me and I've done all the same

 

[Jppr26]

The seal on my old cap was tight going into the new radiator, my thinking was that it took too much pressure to push it, the truck never got above 210°, but I have noticed that it still fluctuates between 155° and 210°, I’m thinking about getting a lower temp thermostat, it has a new stock temp one in it now. It just bugs me seeing the gage jump up and down

 

[436'd skylark]

If your blowing caps off it sounds like your building pressure in the cooling system from a bad head gasket or cracked head.

 

[Obwonkonobe]

The seal on my old cap was tight going into the new radiator, my thinking was that it took too much pressure to push it, the truck never got above 210°, but I have noticed that it still fluctuates between 155° and 210°, I’m thinking about getting a lower temp thermostat, it has a new stock temp one in it now. It just bugs me seeing the gage jump up and down

Its worth a shot, mine just stays right at 180, im using the stock gauge tho

 

[75gmck25]

Do not try to fix temperature issues by installing a lower temp thermostat. All that thermostat does is define a low point for opening, and the rating has virtually no effect on the high temperature of the engine, or any temperature fluctuation. For most street-driven engines the best temp is a stock 195 degree thermostat. I prefer a high flow thermostat and high flow water pump, but its probably not needed for a stock engine.

You may have an air bubble, or some of the coolant lines might be misrouted or missing. Thermostats work best if they have a 1/8" hole drilled in them to allow a small amount of circulation before they open. The heater lines should be hooked up in the stock configuration. On some trucks the heater return line goes to the radiator, while others return to the water pump.

If you are using a 14-16 lb cap and its blowing off, something is not working right with the system.

Bruce

 

[Jppr26]

So I have the new cap on and it fits a lot looser, the rubber on my old cap was swollen and creating too much resistance for the cap to vent properly I believe, the temp gage dose jump around a bit still, but I am still running straight water flushing the system. It also don’t help that I’m only driving it on weekends occasionally, so not really working kinks out to my fullest potential