The Stovebolt Site Forums The Shop Area Engine Shop Drilling a hole in the thermostat ? NEW UPDATE... PROBLEM....

Good idea, or bad?

Advantages, Disadvantages?

Where, and how big (diameter/drill bit size) ?

Thanks! - Lee

I do, about 1/32" - 1/16" or so in the flat part of the flange.
Don't figure such a small hole can do any harm and it might help burp air out occasionally.

Grigg

Google..........thermostat bleed hole............images, you will get dozens of photos of what others have done, plus what shows some stats come stock with a bleed hole.

Or just buy a stat with a jiggle pin...allows the stat to bleed air but acts like a check valve so that only air will pass, not coolant...the Duralast stats from Autozone for the 216/235's have them as well as a few others.

Matt

Well, I guess I shudda started this thread with the problem first, because I did a lot of work today and still have the same result/problem.

When I start driving my truck, the temp gauge gets up to 220 quickly, so I turn around and head back to the house, and by the time I get there, she's a cool 180.

I assumed my thermostat was sticking upon start-up so I drained the coolant, ran a full complement of water thru it, got it up to operating temp, then drained the water, changed thermostat (new 180) (drilled a 1/16" hole), new hoses, and filled her up w/ 50/50 prestone from the thermostat inlet.

Left my shop, the temp gauge AGAIN pegged to 220 about 1/2 mile down the road, I turned around, went back home and by the time I got there, AGAIN it was sitting on 185/190 and I couldn't make it get any hotter than that.

It's 98 degrees out today and after it cools down from the initial 220, sitting/idling, running at 25mph in first gear, or 55 in third, she still sticks at 180-ish.

Why am I getting this 220 degree spike for the first 5-10 minutes?????

(OBTW, I ran the truck with no thermostat and it never got over about 140-150, certainly never got close to 220).

Does the location of the temp gauge (back of the engine) get hotter than the front where the thermostat is.... and takes a while for the cooler water to get back to the gauge???

I'm baffled....

Is your heater connected? If the hoses are routed properly, coolant should be circulating from just under the thermostat back to the water pump inlet and the hot spot that naturally forms under the thermostat shouldn't happen. There's also a modification that can be done to the lower thermostat housing to create an independent bypass circuit which will positively eliminate the temporary high temp situation that's common while some engines are operating with the thermostat closed.
Jerry

Probe location sure will effect the readings. The back of the engine sees less water movement till the thermostat opens, since moving water will take the path of least resistance. If you can circulate water, then the spike will go away. I relocated the temp probe on my 250 to the port right under the thermostat instead of the cylinder head. Mine would spike just as yours is doing. My heater hose has a vacuum shut off valve to stop flow to the heater when not in use, so the small bypass built into the cooling system wasn't enough to really keep the temp even across the head. Once the thermostat opened, the engine stayed steady at 180. I no longer get the spike and I know just what the temp is leaving the engine.

I figure as long as the temperature leaving the engine is right, I don't really care what it is doing back in the head or block.

My truck doesn't have (nor never had) a heater, Jerry...

Yeah, Joe, I think that's exactly my issue as well. I let my truck cool down several times yesterday and the result was always the same: After start-up the temp spikes to 220 and within a minute or so falls to 180, and everything in the cooling system is new. The thermostat obviously creates the issue, as when it was out of the motor the temp never got above 150. I too think it's the location of the temp sender, so I'm gonna ignore it, as long as it continues as is. Maybe I'll move the sender like you did. Thanks everyone for your sage advice. You guys really have helped me greatly!

Change the thermostat.
The 48 2 ton had a Southwind gas heater so no heater hoses.
Ran both 160 and 180 degree thermostats with 3/32" vent hole and never had any transients. Temp climbed and leveled at the correct place every time.

I did. I put a new one in and it did the same thing. Or, were you suggesting I put a cooler (160-ish?) stat in?

As long as it's not boiling water out, stays at a steady temperature, and you can live with the temporary spike, then problem is solved.

Mine was like that for 12 years!

Joe

I'm attaching a link to a thread that includes instructions about how to convert a 235 thermostat housing to one with a bypass. Relatively easy project to do. Works great based on how I have been testing it this summer in the Arizona desert. No spikes, fast engine warming, more consistent temps and lower temp readings than before.

https://www.stovebolt.com/ubbthread...ing_a_216/235_thermosta.html#Post1163318

This version will only work on a late model 235 or 261 with a low water pump, not a 216/early 235 with a high water pump or a late 235/261 converted to a high water pump. The high water pump does not leave enough clearance between the new bypass port added through the base of the thermostat housing and the water pump.

As stated in the link, Hotrod Lincoln and I were working on a version for the high water pump engines. We have a solution figured out that uses a stock thermostat, but neither of us has built a prototype to test yet. If anyone is interested in moving forward with the project, I can share where we left it and someone can take it from there. I have a few extra thermostat housings that I collected for the project that I'd be happy to send to someone who wants to move the project forward.

Matt

Thanks Matt. My truck is a 53, but the motor is a '55 235, so it may not be a candidate. I'll check out the thread! Thanks! I'll get back with you! -Lee

One last thought.
Do you have an overflow tank?
It is the only way to insure that you have purged all the air from the system, and a recurring air pocket in the block could account for the initial spike.
I used an (repro) original style metal tank on the firewall, and properly modifies the cap.
One note, disregard the instructions to install it empty and empty it later. Always install it 1/3 to 1/2 full to allow the air to escape and coolant to be drawn back in.

No, Jim, I only have an overflow line dumping to "the world" at the bottom of the radiator. Interestingly, I started the truck tonight, and slowly creeped around the farm in first gear for about 30 minutes, and it never got to 220. 190 maybe, but at idle speeds up to maybe 2000 rpm, it never got HOT.... Hmmmm

Hello, I would like to resurrect this post
I am having same issue with temp spikes just like Maddog had
Please help!
It will drive great, get up to 220 and hold
When I turn the truck off, and immediately start and rev a little, it will drop down to 180
I checked the temp gauge in a cup of boiling water against a thermometer and the gauge checks out

It could be as simple as purging air from the system. Loosen the temperature gauge sending unit on top of the head and fill the radiator until coolant starts to weep out of the fitting, then snug up the sending unit. Since the sending unit is at the very top of the head, this insures that all air is out of the block when filling the system.

Matt

Thanks Maybellene, done this twice already... still same issue; what puzzles me is temp goes to 220 and holds. when I turn the truck off, and re-start in say 20 seconds, and revving a little, it drops to 180.
My truck is running rich right now and heard this could be part of the issue?

Please see video
http://s430.photobucket.com/user/lo...BB2-0487-4F70-A52E-7B7B7C444FA6.mp4.html

Just went through this and posted it on another post having a cooling problem. Get yourself a good laser temp gun. You will be able to see where the heat is and locate the problem. I also don't trust gauges until I check them with the laser. Sounds to me like you are having the same issue I just had. The cooling ports plugged at the head gasket causing a coolant flow restriction. The laser temp gun will allow you to pinpoint where the problem is, hope it helps. Troy

Your thermostat might not be working correctly. Try running it without a thermostat and see if the problem goes away. If it does, you found the problem.

Thanks, I will
It is the 2nd 160 deg thermo I have used; this truck sat for 30 yrs before me and I still have not found the culprit

Removed thermostat and truck stayed at 100+
Took along time to get to 140 and then 180 max but dropped after driving for a bit
Puzzling how (2) 160 deg thermos failed

The Chinese calibrate differently than us!

To test the thermostats put them in a pan of water and slowly heat it up while monitoring the water temperature with the wifes cooking thermometer and see what temp they open.

Mike B

Well, the good news is that you found your problem and the fix will be cheap! The thermostats work with wax that melts inside the sealed area causing th plunger to open and close. For some reason, you faulty thermostats appear to be sticking when opening and/or closing the way you describe the cycling. I'd pitch them both and try a new one from a different manufacturer.

For what it's worth, the AutoZone's private label Duralast thermostats come with a jiggle pin for both the 160 and 180 degree versions. I'd go with a jiggle pin version over one without any time.

Glad you found the problem,

Matt

I have been drilling bleed holes in thermostats for 30 years. I have seen more shadetrees blow head gaskets due to an air-bound cooling system than I care to talk about. lol

SOME modern engines though have such sensitive temperature sensing equipment that drilling a bleed hole in the thermostat will actually cause a check engine light. I have seen this personally on late model GM stuff.