Inliners International Forums General Discussion Engines temperature sending unit

I put in a mechanical temperature gauge on my Chevy 250 with 3K on it and installed the sender in the head on the drivers side. Its about 6 inches in from the front of the engine where there used to be some sort of temp switch that didn't seem to switch anything. The reading on the gauge is consistently between 225 and 230. Seems a little high to me and I'm wondering if it has to do with the location of the sender. The other three places I could've put the sender were on the thermostat housing where there is the idiot light sender, a vacuum hose temp switch and a plug. Where have other people put senders on their 250s and how hot do they run? Thanks, Keith

i come off the thermostat housing

I went off the right side of themostat housing and the mech. temp gauge sendor would not clear normal thermostat had to use shorter(Robert Shaw)type .

A lot of mechanical temp gauges are not really that acccurate.Dip the sensor into a pot of boiling water and see how close it reads to 212 degrees on the gauge.

Before my mechanical temp gauge turned to junk I had it installed in that same spot on the head and it worked and read correctly. I replaced it with an electrical gauge and sender, again in the same spot and it also reads correctly. Both gauges verified with an infra red thermometer.

I use the tapped hole under the thermostat for the temp switch for my electric fan.

As was said, verify the gauge is reading correctly before replacing it or getting into cooling system problems.

So, is 230 degrees at the head too hot? I just put in a repaired rad and 7 blade flex fan. Seems I ought to be doing better. K

My 250 will hit 230 at if I idle too long on hot days (100plus)but when I get moving it will drop under under 210 quickly, and it's 60 over with alot of compression. I say 230 is too hot for just cruisin' cause bone stock they can easily run under 180.

I'd be concerned about a 250 that wanted to run at 230 degrees. My 250 is 30 overbored and runs just under 10 to 1 compression. With a 180 thermostat and a 14 inch electric puller fan and a Walker 3 row radiator it runs all day long in summer heat at highway speeds between 180 and 185.
Around town it runs right on the 180 peg and idling in summer traffic for extended periods it will climb up between 190 to 195.

What are you running for a thermostat? What exactly is the radiator? Flex fans are not my favorite but I doubt it is the biggest part of your temp. Detail out the cooling system for us and we might be able to see some ways to help you.
Chevy 250's never had a reputation for being a hot running engine. If yours is stock or close to it then something isn't doing its' job.

To add to what Mike is asking,
verify the thermostat is working corectly also.

Is this a freshly rebuild engine that's still tight, or ???

Fresh engines can run a bit hot until they break in.
Tired old abused engines could run hot from a bunch of crap, barsleak, etc... clogging up the block...

Dear Keith;

Mike & Brian are correct as 230 degees is to hot. It's true for most other engines as well.

A new/rebuilt engine (with 3,000 miles) will run a little hoter as mentioned, but not that hot.

Replace the thermostat with a 160, making sure It's in the right direction of flow.

Good luck.

Don't forget to check your timing!!! An advance timing (Or loose distributor)will cause your temp to go up too high!

RapRap
1940 ChoppedChevyCoupe

Have you tried a new radiator cap? If it isn't holding the proper pressure you can run hot. Some times its the simple stuff.

Thanks for all the suggestions! It is a new rebuild with about 3k on it. Its has a 3 row rad that was cleaned and tested, new rad cap (7 lbs. psi per rad guy who said lower psi will extend cooling system life-maybe that's it!).
I added the flex fan. Mike, what is it you don't like about flex fans? There was a five fixed blade fan originally. I thought about adding a fan clutch, but there wasn't enough room.
I'm going to test the gauge and the thermostat as suggested and swap in a 13 lbs. rad cap.
I've also wondered about the timing as there is a brief hiccup or dieseling when its shut off. The timing plate is wierd with what looks like an "A" with a bunch of evenly spaced marks and then an "O". Not sure what those mean. Anyone?

Thanks again for all the advice! Keith

The "A" is for "advance" and the "zero" stands for "top dead center", but like the other guys have said,( first things first) you need to know your temp reading is accurate.Glad to be of any help and good luck.

There are good flex fans & there are crappy flex fans.
Some will rob a lot of HP, others not that bad.
The worst flex fan is the plastic type ,the better fans are the stainless type.
You should not overheat w/a 7 blade flex fan.
What size/diameter is it?
Do you have a fan shroud?

K;

A 7# cap is just fine as the radiator guy says. The only time you need more pressure is with A/C in the summer months.

Stock fans are okay, especially W/O A/C etc.

There must be another place besides the thermostat housing for the sending unit. Why wont it fit in the head, perhaps an adapter is needed.??

Put a guage in the radiator & see what the temp is there. Then you'll know what is going on.

Okay, I tested the gauge and its accurate (Wife says: "What are you cooking there, honey?"). I also tested the thermostat (195 degree) and it didn't open soon enough for me. So I replaced it with a 180 degree and the gauge reads just under 200 in Park, 205 at idle (600rpm), and 195 with my foot on the gas in Park. I guess thats okay for a rebuilt engine with 3k on it?

I'm working on repairing the shroud and when I put that back we'll see how she does.

One thing I noticed checking the timing, vacuum, and carb tune was that the timing mark on the engine damper/pulley is not the factory mark. The installer (really it wasn't me!) painted a line across the damper/pulley that is about 90 degrees away from the oem mark. So I used the painted mark and the vacuum gauge to get the timing as close as possible. I am assuming the installer got the distributer installed a little off and thus the new mark. Is this a big deal? And, why would a straight six need a vibration damper-or is that just a fat pulley?

Thanks, Keith

1978 Checker Cab with 250

Sounds like things are working out The only way to be sure of where your TDC mark is is to check it your self. I recomend you read the Chevrolet Inline Six power manual by Leo Santucci it covers just about every thing there is to know about the 250, including how to locate TDC.Also if your trying to set your timing to factory specs you need to set it with vacuum advance disconected.

What Hank said about flex fans plus the fact the stainless units are like razor blades. Not even thinking about shoving a hand near it while the engine is running, just having to work near a stationary one is dangerous enough.
The temps you now are getting seem a lot better and might drop a bit after some more miles and things loosen up slightly. Another consideration is the coolant mix you use. Plain water will give the best cooling and the lowest operating temps but overall isn't very good for corrosion protection, etc. A 50/50 mix of glycol anti freeze and water will typically result in a 10 degree higher operation than plain water. I've experienced this time and again over the years.
You don't want to run plain water but limit the mix to 10 above or right to zero if the vehicle is garaged in the winter and you will be better off than a mix for 40 below unless you live on the north slope of Alaska. Glycol also raises the boiling point so it all becomes a little bit of a trade off when deciding what % to mix.

K;

Yes; you really do need a dampner.

To set the timing (engine running) simply retard it till the engine stumbles & then advance till it just smooths out. That is TDC for your engine.

You can then check if it matches the marks etc.

The vacuum advance is disconnected & the line pluged as always.

It's still way to hot. Try running it W/O a thermostat for a while.

Good luck.

PS: The dampner you have is probably old and has 'slipped' causing the past owner to mark it etc.

This is a pic of the shroud prior to modifications. The hot running problems I encountered above were when I replaced the cleaned rad, but didn't put the shroud back and used a flex fan. The temp seemed to go up when I accelerated sometimes to 230. At idle it was fairly steady at 210-215. With a 180 degree stat and rebuilt engine with 3k on it.



Here's a pic of the shroud modified and replaced. Now the engine seems to idle steadily at 200 and with acceleration drops to 190 or so. Haven't driven it enough to see how acceleration changes things. Note I used the original fixed fan. Now I'm thinking that there is something with the ignition causing the hot idle. I think the distributor is the original and not rebuilt with the engine. I also tapped the crank and replaced the balancer. When I switched out the old balancer I noticed that the oem timing marks were identical to the new one-so maybe it hadn't slipped. The original balancer had a painted line about a quarter turn back. Going to check the timing next. Any other ideas?

This may sound stupid but i just went through this with a buddys '55 Ford. Was doing the exact thing yours is. He had put his fan on backwards. He had run it like that for a couple years. Doesn't hurt to check.

Cheers!