Cylinder head gasket replacement job

[Andrew Koetz]

The engine in my 84 is either a 1973 or 1974 era 350 there is no coolant leaking from the water pump nor the head gaskets at this time. I am thinking it may have an electrical issue with the temp gauge as I installed a new sensor. The trailer harness was mucked with before I bought the truck by the original owner; a Texas rancher. The truck was ordered with a 7 pin trailer harness and it also has a 4 pin which does not work. I found the trailer wiring under the hood to be intact; it's at the rear of the truck where teh wiring harness was messed with. I had to help with a delivery for work with a trailer I have at home that was low profile and I discovered the harness was not working then.

 

[Andrew Koetz]

The original temp sender had a round flat disc on the end of it with a crimp terminal that slid over it. I did not like that setup from the get go; I purchased a new sender that had an actual mae blade on it the sending wire I know would have a solid connection on it. I also changed the connector as the connection at the time was questionable as the temp gauge was not getting anything for a reading. A friend of mine said the gauge may not be getting a ground through the circuit board; this is where I am considering installing a separate ground between the gauge & the firewall.

 

[Andrew Koetz]

The truck is not overheating (nothing visual) except the overflow jug is almost full if that means anything.

 

[Andrew Koetz]

I changed the radiator to see if that would cause the temp gauge to drop as well as the transmission cooler. The radiator appeared to have some crap on it that was built up & dried crusty; the cooler for the trans had mummified oil on it from the A/C condenser. I still need to get that stuff power washed out of the condenser yet. The only part I have yet to look at is the heater core to see if it's plugged or not. If that's plugged is there a way to use air pressure to clear it with my compressor and an air gun????

 

[Ricko1966]

Verify it's getting hot I think you are chasing ghosts. Let some air out if the tires maybe it won't get as hot,change the wipers see if that does anything.

 

[75gmck25]

There is only one ground for the entire instrument cluster. If it’s disconnected you will have multiple gauges and indicator lights not working. It’s not an easy fix to add a separate ground to the temp gauge, since you need to remove the cluster first, and I doubt that is the problem anyway.

GM changed the temp gauge sending units over the years, and you may simply have a mismatch. Did you buy one for the year of your truck or the year of your engine? The one for a ‘73 or ‘74 engine will not give a correct reading when used with an ‘84 cluster.

 

[Rusty Nail]

That was my thought ^

Rick is prolly right too but don't tell him I said that!


Wrong sender. Definitely a different part number between 74 and 84 - the difference between standard and metric.

Hope this helps!

 

[Rickf]

I did install a new temp sender a couple months ago; the same time I swapped the temp gauge

Was it running hot before you messed with it? Did the replacement sending unit look like the old one? Could have mistakenly installed a sender for an idiot light?

 

[Andrew Koetz]

It's what the parts guy gave me & it spun into the side of the block just like the other with no issue.

 

[Andrew Koetz]

My truck may be a 1984 model but the 350 in it is from the 1970's. So maybe I need to change the sender again; only ask for one for a 1970's Suburban this time.

 

[PrairieDrifter]

My truck may be a 1984 model but the 350 in it is from the 1970's. So maybe I need to change the sender again; only ask for one for a 1970's Suburban this time.

No. The sender needs to match the gauges. You're making this way more difficult on yourself.

 

[75gmck25]

The sending units are either 1/2” or 3/8” threads. The size difference is very easy to see. Most 350’s I’ve seen have the large one, but I’ve seen heads for 307’s that uses the small one. There are no sending units I know of for a stock SBC that use metric threads.

The sending unit and gauge must be for the same year, so you must match it to your cluster. All of them simply use the gauge to measure resistance of the sending unit, but the resistance profiles are different.

This article has some info to explain. IIRC, a TS6 works fairly well with my ‘75, since the original ‘75 sending units are no longer stocked. https://www.metroli.org/pdf/Temperature Sender Resistance Chart.pdf

 

[GTX63]

Yes, both sending units will spin into the head but they have different resistance. I have a 74 with a late model sending unit and it reads very low.

 

[Ricko1966]

1984 your temp sender should read 1,365 ohms resistance when cold if yours is significantly lower you have the wrong sender. 67-79 should read 350 ohms cold.

 

[Copymutt]

I would have checked the temp at the t stat w/ a hand held infrared gun B4 getting further. Also works for finding dead cylinder. Just point it at each down tube.