new 250 runs hot?

[cookeemann]

Running hot. Should temp sensor be in thermo housing?

- Brand new rebuild, 250ci
- New rad, water pump, temp gauge, hoses, thermostat
- Elec fan
- During break in run, temps got too hot for my comfort - 225* and I shut it off
- Temp sensor in head between cyl's, should I move it to thermo housing?
- Top hose hot, bottom cold
- Thermo verified opens in boiling water on stove
- Timing set with vac advance plugged, 4, 8 and 10*....all same result
- Runs rich, black tailpipe smoke

I'm stumped and really don't want to think the machine shop messed it up.

- Why is it running so hot?

Any ideas? Thanks Gurus!

[Isaiah92260]

Originally Posted by cookeemann

Running hot. Should temp sensor be in thermo housing?

- Brand new rebuild, 250ci
- New rad, water pump, temp gauge, hoses, thermostat
- Elec fan
- During break in run, temps got too hot for my comfort - 225* and I shut it off
- Temp sensor in head between cyl's, should I move it to thermo housing?
- Top hose hot, bottom cold
- Thermo verified opens in boiling water on stove
- Timing set with vac advance plugged, 4, 8 and 10*....all same result
- Runs rich, black tailpipe smoke

I'm stumped and really don't want to think the machine shop messed it up.

- Why is it running so hot?

Any ideas? Thanks Gurus!

Mine runs at 200-210 in 100 degree weather. So far it runs good to me. I have my thermostat sensor at the T-Stat housing. I've heard that having the sensor at the head will give you a slightly hotter reading than Having it at the T-stat housing.

[siggyfreud]

Really only a few things it could be.

1. Coolant flow (but your thermostat is working you said). Ensure top and bottom hoses get warm to verify you have flowing coolant in the motor.

2. Air pockets. You could have large air pockets in the system still and may need to burp the system.

3. Air flow. It's possible the electric fan just isn't moving enough air. Is it a dual speed? If so, is engaging high speed?

4. Engine issue raising temps, like a blown head gasket. Unlikely on a new rebuild if you did it right. This would be the last area I looked if other things checked out.

5. You said you're breaking in the engine right? Does that include RPM's above idle? If so, the fan may simple not move enough air, even on high speed to cool it. When I break in a motor I use a couple of space fans at the front to also keep the engine cool. Electric fans need to cool the motor at idle and slow speeds. Beyond that airflow through the grill cools it. If you're running at 2k rpm to break stuff in, but have no organic airflow that's likely why you're overheating.

[padresag]

Originally Posted by cookeemann

Running hot. Should temp sensor be in thermo housing?

- Brand new rebuild, 250ci
- New rad, water pump, temp gauge, hoses, thermostat
- Elec fan
- During break in run, temps got too hot for my comfort - 225* and I shut it off
- Temp sensor in head between cyl's, should I move it to thermo housing?
- Top hose hot, bottom cold
- Thermo verified opens in boiling water on stove
- Timing set with vac advance plugged, 4, 8 and 10*....all same result
- Runs rich, black tailpipe smoke

I'm stumped and really don't want to think the machine shop messed it up.

- Why is it running so hot?

Any ideas? Thanks Gurus!

new engines can run a little hotter at the beginning if they are a little tight. if you sit and let it idle it should cool down faster than shutting it off. they can get hotter shutting them off right away
the sending unit will read the temp what it is at that location. it drops at the thermostat housing.
water boiling on the stove is 212f. it should open at the temp that is stamped into it. you should use a thermometer that goes up that high(cooking thermometers are the ones to use. just don't get caught as they don't like you using that stuff on car parts.
did you bleed the heater?
225 f is not a problem if you have the proper rad cap and coolant mixture
ron

[vince1]

The top hose is hot so it must be circulating. It could also be confirmed by watching he fluid with the cap off. Eventually the lower hose should get warm. Did the fans ever come on?

You're way more advanced with yours than mine. I have the original two terminal hot cold switch at the T stat housing which operates the hot and cold light. I don't know what temperature it is running at other than one light goes out and the other doesn't come on.

[padresag]

Originally Posted by vince1

The top hose is hot so it must be circulating. It could also be confirmed by watching he fluid with the cap off. Eventually the lower hose should get warm. Did the fans ever come on?

You're way more advanced with yours than mine. I have the original two terminal hot cold switch at the T stat housing which operates the hot and cold light. I don't know what temperature it is running at other than one light goes out and the other doesn't come on.

if it is up at that temp your not going to take the cap off
ron

[vince1]

I was thinking cap off and then watch it after start up.

[padresag]

Originally Posted by vince1

I was thinking cap off and then watch it after start up.

so if it goes to 225 f with the cap off the it will boil. the cap puts it under pressure and raises the boiling point 3 degrees for every lb of pressure. you were on though on the other , putting your hand on the uppers wwill tell you whether it is hot or not
ron

[vince1]

I would think that if it boils with cap off and bottom hose cold at no load idle something is wrong.

[padresag]

he said that his thermostat opens at boiling on the stove and this is what you said, " Eventually the lower hose should get warm". it could then be theoretically possible to boil then at the top and be cool on the bottom, though that may point at a problem with his thermostat.
but I think that we are getting off track of his problem
ron

[60chevyjim]

I would try it without the thermostat in , and the cap off and see how the water flows .
starting it cold and see how hot it gets . both hoses should get hot .

[chevy_mike]

When I first put my rebuilt 250 back in my '64 Chevy II wagon, it was running way hot. I had the aftermarket temp sensor in the head but when I used a IR temp gun to check, coolant wasn't as hot as the gauge was reading. I put the sender back into the t-stat housing and temps were back to normal, matching the IR gun. Being in the head seems to pick up more heat since it is right by the combustion chamber.

Move your sender and see how it goes.

[TJ's Chevy]

My 292's sensor was in the T-stat housing. Much more accurate reading. On a 100+ degree day it would never get much above Normal. And under the hood really didn't feel to bad either...my guess around 200. Some tips for break in....use a large shop fan to aid in cooling. We did this with dad's big block chevy 572 and it Never got past 200 during break in! Even when the timing was Waaay to far advanced-which was remedied and the engine ran cooler- it never went past 200. Try a shop fan as well. When the timing was set a little better the engine ran at 180-195 for the rest of break in.

[siggyfreud]

Originally Posted by chevy_mike

When I first put my rebuilt 250 back in my '64 Chevy II wagon, it was running way hot. I had the aftermarket temp sensor in the head but when I used a IR temp gun to check, coolant wasn't as hot as the gauge was reading. I put the sender back into the t-stat housing and temps were back to normal, matching the IR gun. Being in the head seems to pick up more heat since it is right by the combustion chamber.

Move your sender and see how it goes.

Or adjust your comfort level for what too hot is . I like my sender in the head, because ultimately that is the temp that I care about. No engine went toast from having a thermostat housing get too hot, but if the heads overhead . . .

Either solution works really, but if it were me I'd just get comfortable with whatever the new measurement really means, what is now too hot, etc.

[grubsster]

The issue I had after installing my 327 was the new temp sensor I had purchased from the parts store. My gauge would go completely to the H after about 5 minutes of running. I was thinking the engine was running hot but when checking with an IR temp gun my heads were right at 190. I determined the temp sender was the incorrect resistance and ordered one from Lectric Limited. Now my gauge reads correct.

[luvmytruck]

Originally Posted by padresag

new engines can run a little hotter at the beginning if they are a little tight. if you sit and let it idle it should cool down faster than shutting it off. they can get hotter shutting them off right away
the sending unit will read the temp what it is at that location. it drops at the thermostat housing.
water boiling on the stove is 212f. it should open at the temp that is stamped into it. you should use a thermometer that goes up that high(cooking thermometers are the ones to use. just don't get caught as they don't like you using that stuff on car parts.
did you bleed the heater?
225 f is not a problem if you have the proper rad cap and coolant mixture
ron

completely agree with what is said here and an engine running without enough timing advance will run hotter. but for a new engine 225 is not bad, 240 would start to concern me

[cookeemann]

Update:
All, thanks so much for your advice. All very good points.

For me, the debate over where the temp sender should go is over. I moved it from the head to the thermo housing and my temps are right where they should be. 190-210 and I watch the needle rise and fall as the thermo opens......all with just straight water (was all I had in the shop). So I'm thinking it was just a sending unit location issue.

I'm a jeep guy and have done many 258 inlines and the temp sender on all those are in the intake, so moving mine to the thermo housing made sense to me.

Temps rock steady, runs like a champ, but haven't driven it yet.
I'm thankful for this forum and all who took time out of their day to help. You are all very much appreciated.

[vince1]

I have a 232 in my 64 Rambler and it was overheating. Surprise, surprise, finding the water pump plastic impeller in pieces down in the bottom rad hose. That is something to watch for in the old engines. I don't know if GM did that too.

So, which is the better engine, the AMC 6 or the Chev 6? I guess they are both good except that you can't change lifters on the AMC 6 without taking off the head. The AMC 6 had a pretty good run from a 232 in 64 to the 258 and finally the 4.0 which Chrysler used until I think 1996. But there's so much spaghetti over those later engines you can hardly find it in the engine bay.

Some day I might like to try a 4.2 out of a Trailblazer in my truck but the lottery will have to come through first.