[77 cruiser]

This is a 95 GMC 350. The temp cycles between 210/15 to 160/170 or so. I'm running a 205 thermostat, trying for a little more heat for winter.

The cycling has been going on for a couple years. It's worse the colder it is outside.
I've tried several new thermostats.

New water pump, the other one had a leak. It seamed better after the pump change, but now it's bad again after putting the 205 thermostat in.

The only way I gotten out of it was a 195 stat with a small hole big it delayed warm up, even with a 1/16 in hole, & I want it to warm up as quick as possible when it's -30 or lower.

Any suggestions would be appreciated.:bow:

 

[yellow heap]

Air in the system can cause that-I always drill t stats to prevent air pockets.
I run a 200 in the winter with a 1/8 hole in it and about 1/2 to 3/4 of the radiator covered with cardboard.
A mech fan will delay heat up even a idle at REAL cold temps and the blocked radiator helps .
Not as cold here as you-I know YOUR cold,I was born & raised I Baudette Minn.

 

[77 cruiser]

Baudette Bears
If I can't get it figured out I'll probably drill the hole. I guess I can't see how air could be trapped after the stat cycles open. If I have a combustion leak, I would think that after a few years it would've shown up as something more serious.

 

[yellow heap]

Try the cardboard-I'm already at 1/3 blocked and by the time Dec rolls around I'm 3/4 with a Mech fan it makes an even bigger differance in warm up.

 

[SWHEATON]

If it not air in the system or simly a bad t-stat then its the motor is simply heatng up to 210 or so then the 205 stat opens sending much cooler coollent back into the motor where tem sending unit is cooling it down to 160-180 and then the stat partially closes againg because of much cooler coolent hitting the stat/motor and that stats the cycle all over again and again which should stabilze in time unless you too too much cooling capacity.

I bet you have too good of a colng system which can cause that to happen and also,if running a severe duty or even hd fan clutch try changing to a lower perf std duty fan clutch that will also reduce rad cooling efficinecy some esp when at idle in traffic doe toless fan lockup/less fan rpm with std duty fan clutch vs hd or esp severe duty fan clutch.

Id also dith the 205 stat & try a 195 stat and if you cant get temp to stabilize at 190ish after running 20mins tor so hen try some cardboard as already suggested.

I'd,start with covering approx 1/4-1/3 of rad max and see how that doese then report that back here. You can spray paint the carboard with satin/lowgloss/or fla blk to hide it ans also prtect it from rain/water too.

And if you find that did the trick then you could cut some flashing to same size as carboard that stabilized the system and pait it black then install that for a more perminant/professional looking fix.

You could als drill 1 hole in each of 4 corners of flashing and then use the nylon strips that are used to install elec fans to rad cores to hold the freshly painted satin/flat black flashing to the front of the rad core for a nice clean look.,it wont rot or degrade like cardboard thats painted could do over time/miles & esp with plenty of rain/water hitting it at tmes.

Scott

 

[77 cruiser]

Yea it must have a good cooling system as it never runs hot even pulling a 26' camper. You might be on to something Scott.
I might try covering the rad a bit & see what it does.
I did drill a 1/16 in hole & that helped.