Hey guys so I got my car out on the road, I have never changed the temp sending unit but it seems like as I got faster or more RPMs the temperature rises sometimes almost to the red line but when I slow down or stop the temp lowers back to the middle of the gauge or even lower. I flushed out my rad the other day cuz there was some debris but it’s looking a lot better now. And it runs a tad more rough the hotter it gets, at idle. And suggestions? I got a new temp sending unit coming because I’m pretty sure mines the original

 

It may be time for a tune up. Fuel mixture and timing affect temp.

 

Already did all that. Thats why it’s just not on the road. It doesn’t go into 4th gear so im not sure if the high RPMs are affecting this. According to the manual it says if the temp gauge doesn’t go in the red then its fine which is kind of odd to me

 

Doubtful but it could be a water pump. If the blades on the impeller are deteriorated the pump would not be moving enough water. The regular pump had six blades on the impeller and the AC version had 8. It is natural for a car to run warmer at a higher RPM. I had an under dash gauge in the 54 I had. That way you know exactly what the water temp is. Has the radiator been cleaned out and is it moving enough air through it. You could have derbis and bug limiting the air flow.

 

no water pump is brand new. It is possible there’s still a tiny bit of debris in the rad which I just flushed out. Is there a proper way to clean the rad out? Even the block?

 

or is it possible it’s just my very old temp sensing unit?

 

I would think the no 4th gear problem would be your 1st concern?? Fix that first.
Verify exactly what the temp is with an actual gauge before throwing parts at it... a known accurate gauge or infrared gun.
The system could still be plugged. Air is going around rather than through the radiator or the suction side hose could be collapsing at high RPMs.

 

x 2

 

yeah the trans is on my list for sure. I’m just having the feeling coolant isn’t flowing thru either the rad or the block and wondering what will clean them out best. The other day I cleaned out a bunch of gunk outof my rad now I haven’t seen much but I think I’ll clean out the therm housing. When putting rust remover in the block is better the run it without a thermostat or keep it in to build pressure and heat?

 

im trying but no one is responding to my posts on that topic. Because I have questions about next steps after cleaning valve body and still no 4th

 

Agreed. My car will run at 190º all day long in 110+ Phoenix summer heat with the AC on, but on the highway at 3400+ RPM the temperature will start climbing to 210º. Slow down below 3000 RPM and the temperature drops back to 190º.

 

CRC ThermoCure is a very good cooling system cleaner. It can only be used with water, no coolant so use it in non-freezing temps and let it work for a few days.

Sort out the shifting before replacing any cooling system parts

 

Agreed guys. I did see that thermo stuff online for like 100 bucks is that accurate or is there a store I can buy it in instead of ordering from online? The rpm’s makes sense. But I’ll try post again on another post about my trans cuz no one is answering me anymore and I’ve cleaned that valve body spot less and every piece slid in and out on its own weight. I’m wondering if a band needs to be adjusted with a certain tool because it won’t even try to grab 4 and I didn’t see anything broken when I looked inside, the rear band seemed to be functional

 

ThermoCure is $22 USD on Amazon, $25 USD @ JEGS.

 

I’ll order it cuz we are in summer season now innnew Mexico. I went for a drive tonight temp got up to the 3 quarter mark on the gauge then I turned on the heater and it dropped to just below the half mark

 

can someone check out my 55 hydramatic thread and tell me if loosing or tightening my rear band will get me into 4th gear or is there another governor outside the valve body I need to clean ?

 

temp gun is your friend. to double check temperatures.. , Check vacuum advance, rubber diaphrams give out. Get a timing light with RPM read out.. Ethanol gas doesn't help, richen up fuel mixture a but by changing rods/jets..

Fred

 

higher RPMs are not helping..

 

my timing gun doesn’t have rpm I do it by ear. Rubber diaphragms on what? I just filled it up with 10% ethanol so when it runs out I’ll change it but I really need some more advice on this 4th gear thing

 

noted

 

It could be because very few people on here know anything about these old hydra-matics.

 

After servicing the cooling system with ThermoCure internally remember to not exceed 50% coolant on the refill. Also look at the external cooling fins in the radiator for corrosion, being bent, covered with leaves etc. and the deep in the fins being packed with fine sand.

Good luck with the transmission, I can't offer anything toward the shifting solution.

 

It's best to provide a link to your trans in post #16 above(edit and insert). Save us time having to search. I have some ideas for you.

Have you verified your thermostat is working as it should? Use the KISS approach. I recommend the Stant HD versus standard duty.

 

Therm is working I can see the coolant flowing. But do I remove the thermostat during the thermocure process? I’m not sure how to paste a link but I’ll try

 

I'd leave the thermostat in so it gets cleaned and so that it helps create normal temperature range of the heat cycles. Read and follow the directions on ThermoCure re: letting it work over time, it works differently than the 15 minute drain and flush formulas.

​​​​​​If at all possible remove the threaded block drain plugs when flushing the block. I don't know where they are on your block but someone will chime in.

 

 

I will read instructions

 

For some reason, it's human instinct to gravitate towards the more complex problems first, then work toward the simple low-hanging fruit last. Thats bass ackward.
Not going into 4th gear could be the hierarchal root cause problem which is showing up as a slightly weak cooling system bringing the cooling system into the limelight.

A T-Stat can stick open just enough to allow observation of coolant flow. Or stick open all the way not regulating flow.
Yes, a stuck-open T-Stat can cause overheating at higher RPM.
Why? The coolant is not spending enough time in the radiator to reject enough heat, dumping hot coolant right back into the engine. That effect over time additively will show up as Delta-T creep. (gradual increase in temp over time)

Replace the T-Stat with a 190° HD Stant unit. Road test, with no 4th gear, see if it improves.
The only way to verify a T-Stat is working is by boiling it in the water while observing the temperature Delta-T (change) and watching the stat open....or for 10 bux just replace it. Cheap and quick.

Still overheating at speed?
Trans goes into 4th gear? No, all bets are off until that is fixed.
Cross the T-Stat off the problem list,

Move on to the next easiest solutions:
-airflow
-suction hose collapse
-System restriction...crud.

The system may need a more aggressive cleaning approach. Rodding out the rad and/or a pressure flush of the block & heater core.


To copy and paste the trans thread here go to that thread and highlight the https// in the address bar----> paste into the body of the thread, then click enter. It's as easy as that.

 

I have replaced the thermostat twice this one I have in now seems to be the only one that works which is a 190. I would like to boil it tovisually watch it open all the way. My bottom pan trans gasket is coming today so I’ll tackle it this weekend and I ordered the new temp sending unit as well cuz mine now could be the original. I’ll try to paste the link.

 

says 55 hydramatic olds, I’m doing this all from my phone. I believe your in that thread too

 

Dont do anything with trans pan until I/we see that link. I dont want to hijack and muddy this thread with two subjects.
Do snap a pic or two, if you havent already, of the trans pan. Post iti n that thread. Need to know exactly what model it is.

 

I still can’t figure out how to send the link. You just type in the search bar, 55 olds hydramatic and it’s there. And in that thread is pics of the pan from last time I opened it. It looked not bad there was just some sludge a little bit. I believe it’s a 12 bolt pan but it is a 55 hydramatic automatic 4 speed

 

I had to type in Super88chris to find it. ICKsteve is all I saw when I queried 55 olds hydramatic.

Link to Super88chris's trans thread:

https://classicoldsmobile.com/forums...amatic-177411/

You are in good hands there.

 

yes that’s it and I’ve already asked some questions on it today so hopefully I get some answers thank you

 

Welcome. I just posted there as well.