Cooling System Problem

[trg-42]

I have a stroked 351W in my Superformance. Lately, I the coolant temp ( typically 180 to 210 ) spikes up to 240 and instantly back down

Temp sender is in manifold crossover. Is it possible that the coolant is not flowing ( stuck thermostat ) then flows?

IT has been getting progressively worse now where temp stays at 210 but occassionaly spikes up to 240

Before take out the thermostat housing I want to see if any of you guys have other ideas

Thanks

UPDATE

I replaced the thermostat housing ( and new thermostat with the hole drilled in the top ). Filled it to the top from the sender port and thermostat housing port

I'm suprised how much more coolant the system took. Leads me to believe that there was a hell of a air pocket in there

Strange how the system would over the past 3 months "suck in" air. I think it was from the small leak around the thermostat housing as it cooled

Took it for test drive and temp never got over 190, even in traffic

Thanks everyone for the advise !

[ERA Chas]

You have air pockets in the coolant-the gauge spikes because the air is hotter than the coolant.

You must get all the air out by opening the system (cold) at the highest point (usually the temp sensor on the intake) and filling until the coolant runs outs of the sensor opening. Put the sensor back in, then slowly add to the overflow tank but leave room in the tank for expansion-do NOT fill to the top.

[bobcowan]

I agree. That usually means steam pockets. The question is, where did it come from? It's supposed to be a closed system. Start checking the system for leaks. Consider a head gasket failure.

[Excaliber]

Steam pockets??? Did I hear my calling or was that just Evan's passing through....

[trg-42]

Thanks for the quick reply guys !

I noticed there is a slight leak at the thermostat housing. Perhaps its drawing in air as system cools. When I removed the housing last night, I was expecting a dump of coolant. There was suprisingly little coolant that splilled out

The thermostat housing surface is not flat. I will replace the housing this week and give update

Thank again

[Bob In Ct]

While it's apart, drill a small hole in the thermostat. Place the hole on the top during install.

Are you sure the sensor is OK?

Bob

[JBCOBRA]

+1 Bob on drilling a hole in the thermostat.
Great suggestion for everyone.

[jhv48]

While apart, replace the thermostat.

Spiking temps can be a thermostat sticking. Cheap insurance to replace it and drill that hole too.